Fishpot Creek Watershed - East

Transcription

A Demonstration of Geomorphic-Based
Stream Channel Management Method
February 2003
Prepared by
Soil & Water
Conservation District
Missouri Department of
Natural Resources
This 319 Project was funded in part by a grant from the Missouri Department of
Natural Resources (DNR) and administered by the Water Pollution Control Program,
Division of Environmental Quality. Funds for the grant were made available from the
United States Environmental Protection Agency (EPA) under authority of Section 319
of the Clean Water Act, grant #C9007407-99.
Acknowledgements
The geomorphologic analysis of Fishpot Creek and the report that follows
represent the efforts of many professionals. Ms. Jackie Moore of the St. Louis
County Soil and Water Conservation District shouldered virtually all of the
administrative and public communications responsibilities. She also marshaled a
technical advisory group that provided frank and productive guidance throughout
this entire endeavor. Gary Moore, P.E. of the Metropolitan St. Louis Sewer
District lent his considerable technical skills and management perspective. Gary
also helped the project team gain an appreciation for the improvement in
stormwater management that the District has fostered as well as the magnitude
of the challenges that the District faced in doing so.
Cliff Baumer, P.E. of the Natural Resource Conservation Service offered lucid
comments on the geomorphologic analysis. Ms. Renee Cook of the Natural
Resource Conservation Service and Jim Rhodes, Ph.D., P.E. of the Missouri
Department of Natural Resources helped the team explore the implications for
water quality improvement as well as the financial and public policy issues that
this report raises.
Our project officer, Mr. John Johnson of the Missouri Department of Natural
Resources was consistently supportive and helped maintain focus on the project
objectives; a challenging task given the broad scope and data intensive nature of
this project.
Ms. Jamie Salvo of the St. Louis County Soil and Water Conservation District
assisted in gathering the field data particularly regarding critical sediment
transport parameters. Thanks also to Mr. Steve Gough of Little River Research
and Design who collected extensive field data and whose report is appended to
this document in toto. Ray Hudak of the Natural Resource Conservation Service
identified landowners whose complaints had not been previously recorded and
also conducted early site visits.
Finally, the authors thank the members of the Lafayette Mayors Association and
their staffs for their support in organizing this project.
This 319 Project was funded in part by a grant from the Missouri Department of Natural
Resources (DNR) and administered by the Water Pollution Control Program, Division of
Environmental Quality. Funds for the grant were made available from the United States
Environmental Protection Agency (EPA) under authority of Section 319 of the Clean
Water Act, Grant #C9007407-99.
Equal Opportunity Statement
The Soil and Water Conservation District (SWCD) and The U.S. Department of
Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis
of race, color, national origin, sex, religion, age, disability, political beliefs, sexual
orientation, or marital or family status. (Not all prohibited bases apply to all programs.)
Persons with disabilities who require alternative means for communication of program
information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center
at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA,
Director, Office of Civil Rights, Room 326-W, Whitten Building, 1400 Independence
Avenue, SW, Washington, D.C. 20250-9410 or call (202) 720-5964 (voice and TDD).
USDA is an equal opportunity provider and employer.
Table of Contents
1.0 Executive Summary ..................................................................................................................... 1-1
2.0 Introduction.................................................................................................................................... 2-1
2.1 Purpose of this Project
2.2 Organization of the Report
3.0 Fundamentals of Fluvial Geomorphology .................................................................................... 3-1
3.1 Brief History of Stormwater Management
3.2 How Streams and Rivers Work
4.0 Methodology ................................................................................................................................. 4-1
4.1 Background Data Analysis
4.2 Field Investigations
4.3 Integration of Stream Stability Analysis Into Design
5.0 Methods of Management .............................................................................................................. 5-1
5.1 Energy Management
5.2 The Role of Riparian Vegetation
5.3 The Role of Soil Bioengineering
5.4 Alterations in Plan and Profile
6.0 Results ......................................................................................................................................... 6-1
6.1 Fluvial Geomorphology of Fishpot Creek
6.2 Dominant Fluvial Process
7.0 Rationale for Treatment Priorities ................................................................................................. 7-1
8.0 Proposed Interventions ................................................................................................................. 8-1
9.0 Project Costs ................................................................................................................................ 9-1
10.0 Project Master Tables ............................................................................................................... 10-1
11.0 Comparison between 319 Project Master List and SSMIP Projects ........................................ 11-1
12.0 Conclusions and Implications for Future Management ............................................................ 12-1
13.0 Bibliography............................................................................................................................... 13-1
i
List of Tables
Table 3.2.0 Response to changes in water and sediment quantity ................................................... 3-6
Table 3.2.1 Potential effects of changing flow and geometry parameters on channel stability ......... 3-8
Table 6.1.0 Bedding planes and joint orientation ................................................................................ 6-2
Table 6.1.1 Correlation of drainage orientation to bedrock joint sets ................................................. 6-2
Table 9.0 Project Cost Opinions.......................................................................................................... 9-6
Table 10.0 Projects by Priority .......................................................................................................... 10-1
Table 10.1 Projects by Location ........................................................................................................ 10-4
Table 10.2 Projects by Cost .............................................................................................................. 10-8
Table 11.0 SSMIP and Corresponding 319 Projects ...................................................................... 11-17
ii
List of Figures
Figure 3.2.0 Stages of a river system ................................................................................................. 3-2
Figure 3.2.1 General channel profile of a watershed ......................................................................... 3-3
Figure 3.2.2 Effect of a dam resetting the stream formation sequence ............................................. 3-3
Figure 3.2.3 Effect of stream crossings resetting the stream formation sequences .......................... 3-4
Figure 3.2.4 Channel evolution model ............................................................................................. 3-11
Figure 3.2.5 Discharge centerline in relation to channel centerline ................................................. 3-14
Figure 3.2.6 Meander geometries .................................................................................................... 3-14
Figure 3.2.7 Meander adjacent to resistant structure ....................................................................... 3-16
Figure 3.2.8a Meander advance ..................................................................................................... 3-16
Figure 3.2.8b Hard point flanking .................................................................................................... 3-16
Figure 3.2.9 Meander distortion around extended resistant layer ................................................... 3-17
Figure 5.1.0 Schematic of rock weir .................................................................................................... 5-3
Figure 6.1.0 Rock outcrops ................................................................................................................ 6-4
Figure 6.1.1 Main stem long profile from hydraulic data ..................................................................... 6-4
Figure 6.1.2 Shear values .................................................................................................................. 6-5
Figure 6.1.3 Incising, vertically stable and rock outcrops .................................................................. 6-5
Figure 6.1.4 Fishpot Main Stem shear and specific power ................................................................ 6-7
Figure 6.2.0 Reach Location ............................................................................................................. 6-17
Figure 6.2.1 Geomorphic Observations ............................................................................................ 6-18
iii
List of Figures continued
Figure 8.0 Intervention Overview ...................................................................................................... 8-22
Figure 8.1 Proposed Interventions .................................................................................................... 8-23
iv
List of Appendices
Appendix A .............................................................................................................. Geomorphic Report
Appendix B .............................................................................................................. Reach Descriptions
Appendix C ......................................................................................................................... Photographs
Appendix D ....................................................................................................... Watershed Survey Data
Appendix E ...............................................................................Opinion of Probable Construction Costs
Appendix F ..................................................................................Conservation Stormwater Techniques
Appendix G ................................................................................................................ Glossary of Terms
Appendix H ............................................................................................ Electronic Copy of Final Report
v
Fishpot Creek Watershed
1.0 EXECUTIVE SUMMARY
This report presents the findings of a fluvial geomorphologic study of Fishpot
Creek and its major tributaries. Fishpot Creek flows through the Ozark Plateau in
suburban St. Louis County. It is bordered by seven cities, as well as part of
unincorporated St. Louis County. Like many in the region, this watershed
underwent rapid urbanization in the 1960’s through 1980’s when few stormwater
management practices were in place. The stream is badly damaged with a nearcomplete loss of aquatic habitat and significant physical instability. Not
surprisingly, the watershed’s human residents also suffer from this instability.
Flooding and erosion are common throughout the watershed. In the fifteen years
since accepting jurisdiction for the watershed, the Metropolitan St. Louis Sewer
District (District) has improved stormwater management through watershed scale
hydrologic and hydraulic modeling and the imposition of detention requirements.
This represents a major investment and is a critical step towards systemic
management. However, the stormwater practices remain focused on optimizing
flow conveyance.
In response to increasing complaints from stream side property owners, the St.
Louis Soil and Water Conservation District (SWCD) suggested that a fluvial
geomorphic analysis would provide the information necessary for a more
complete management plan. The analysis was commissioned in November of
1999, as part of a grant from the Missouri Department of Natural Resources
(MDNR) under Section 319 of the Clean Water Act. The District provided in-kind
match for this project with the intent of learning more about how geomorphologic
methods are used to inform stormwater designs. A specific objective of this
project is a direct comparison between the recommendations in the District’s
stormwater master plan (SSMIP) and those generated using the District’s
hydrologic and hydraulic models and the geomorphologic analysis.
The data gathering and analytical methods reflect current stream and river
engineering practice and are generally consistent with those described in the
professional literature including USACE, et al, 2001, Hydraulic Design of Stream
Restoration Projects and USACE, 1989, Sedimentation Investigations of Rivers
and Reservoirs.
We acknowledge that the restoration of aquatic habitat and improvement of water
quality are important goals. However, they can only be achieved by returning the
stream to dynamic equilibrium. The recommendations that follow are intended to
foster conditions for healthy aquatic life in at least the lower reaches of the
stream. This objective is fully compatible with achieving improved physical
stability and resolution of landowner complaints.
This report addresses flood, sediment and erosion management by applying
fluvial geomorphology in concert with hydrologic and hydraulic engineering.
Fluvial geomorphology is the discipline that describes how streams and rivers
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shape the land. It allows the designer to assess how the stream changes in
response to changes in land use and to the quantity of water and sediment
delivered to the channel. The flow of water and sediment is the driving force that
is balanced by the resisting force of the streambed and channel geometry. It is
the interaction between these forces that determines how flooding, deposition
and erosion occur within the stream. Therefore a thorough understanding of both
the driving and resisting forces is required for successful management. A
complete plan for physical stream stability integrates sediment, hydraulic,
hydrologic and geomorphologic data.
Fishpot Creek has adjusted its channel size and shape to accommodate the
quantity of water delivered to it. This adjustment has liberated enormous
quantities of gravel into the stream. It is the generation, transport and deposition
of this coarse sediment that drives the behavior of the stream. Specifically,
several of the headwaters streams are actively incising and delivering the gravel
to the main stem. Where the stream has adequate power, the sediment is
transported with few problems. In the lower reaches the stream power is too low
for effective transport and the deposition of large gravel dunes is responsible for
ongoing and large scale channel adjustment. Arresting sediment generation is a
critical element of any successful effort the stem the widespread bank failures.
In the St. Louis area, as in much of the Midwest, stormwater problems, including
flooding and erosion, are managed as isolated problems independent of the
overall stream system. The consequence of this approach is a series of
interventions that may appear to solve problems locally, but only exacerbate
flooding or erosion elsewhere in the watershed.
The hazards of developing a stormwater master plan without geomorphologic
information become clear when the recommendations in the SSMIP’s are
compared with those in this report. The primary driver for problems through the
stream system, sediment transport, is not addressed in the SSMIP. Many of the
major SSMIP recommendations are contraindicated when stream mechanics are
considered. The primary in-stream recommendations involve channel lining,
widening or both. The adverse consequences of these practices are thoroughly
documented in the civil engineering literature and we noted damage associated
with several of the recommendations that had been installed during our field
work.
We conclude that while the watershed-scale hydraulic model is valuable, the
model and a complaint list in no way constitute a basis for developing a
stormwater management plan. We recommend that the District replace the
capital improvements recommended in the SSMIP with those derived from the
more complete analysis in this report. We recommend a set of treatments to
address each complaint listed in the SSMIP. Each recommendation was
developed to resolve both the complaint and to improve the physical function of
the stream system. Concepts such as matching stable channel dimensions for
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dominant discharges, continuity of sediment transport and incorporating instream structures to reduce erosive shear stress on stream banks influenced
each recommendation.
We have recommended interventions in this watershed totaling $23.1 million.
Priority 1 projects, those addressing public safety and protection of infrastructure,
total $11.7 million. In preparing our cost estimates we included the cost of
surveying, analysis and design, easements, construction and construction
observation. When comparing the SSMIP recommended project costs to the
corresponding 319 recommended projects, the 319 projects have a capital cost
of $14.2 million, which is $3.6 million less than the $17.8 million SSMIP. We
acknowledge that there are five SSMIP projects (FIS-02, 20, 21, 24, and 26) that
were built prior to this report and, consequently, there are no 319 cost estimates
associated with these structures. The SSMIP estimate for these projects totaled
$2.2 million. However, we estimate the cost of ameliorating the unintended
damage associated with the installation of these structures at $1.0 million.
The implications of this project on the future of stormwater management are clear
and compelling. The current approach of complaint-driven management renders
ineffective and even counterproductive treatment inevitable. A systematic
management approach based on the full suite of technical disciplines necessary
to describe stream behavior is more cost effective, functional and
environmentally sound.
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2.0 INTRODUCTION
2.1 Purpose of this Project
This project arose from the desire of all parties involved in stormwater
management to find a more systematic, cost effective and environmentally
responsible approach. The Metropolitan St. Louis Sewer District (District) is
engaged in a long-term effort to improve stormwater management and has
recently completed watershed-scale hydrologic and hydraulic models throughout
its jurisdiction. This alone represents a major step forward and one that many
Midwestern communities have yet to take. The St. Louis County Soil and Water
Conservation District (SWCD), which helps landowners treat erosion and water
quality problems on their property, noted that many struggled with stream bank
erosion far beyond the scope of individual property owners. The Department of
Natural Resources (MDNR) has the challenging task of protecting our water
resources under increasing pressure from urban development. Their efforts to
protect the health and beauty of streams for future generations were often
stymied by the District’s stormwater practices. Faced with mounting complaints
and unaware of an alternative, the District treated our streams like canals and
storm sewers, managed for conveyance and often lined with armor. Despite the
advance in hydraulic modeling, the region still depends on a complaint-driven
process. The consequences of site-specific management are considerable for
taxpayers, stream side residents and the aquatic ecosystem. Bridge scour,
undermined sanitary lines, flooding and erosion are endemic in this watershed
posing a threat to public safety and to public funds. In addition, Fishpot Creek
was once a perennial Ozark Plateau stream. It is now so choked with sediment
through much of its length that it supports little aquatic life. Clearly a
fundamental re-evaluation of our region’s stormwater approach is in order.
The organizations described above have not always communicated well and
sometimes appeared to work at cross-purposes. However despite their different
philosophies and priorities, they share a common goal; protect both our citizens
and our resources.
This project reflects that common goal. In 1998, the SWCD proposed that the
District and DNR consider a new way (for the Midwest) of managing stormwater.
The SWCD played the critical role of honest broker and encouraged the District
and MDNR to acknowledge the role both play in protecting people and water
resources. SWCD suggested that a fluvial geomorphologic analysis of the
Fishpot Creek watershed in concert with the existing hydraulic and hydrologic
models would allow more systematic stormwater management that would benefit
stream side residents, taxpayers and aquatic life. Fluvial geomorphology is the
science of stream form and process. It is this critical discipline that enables reestablishment of a stable stream system. A physically stable stream is the
necessary platform for re-establishing a healthy and productive aquatic habitat.
2-1
The work was funded by MDNR through Section 319 of the Clean Water Act.
One of the specific tasks was to directly compare the recommended
management practices of the District’s Stormwater System Master Improvement
Plan (SSMIP) with those based on the hydraulic model coupled with
geomorphologic analysis.
In this report, we present the results of the fluvial geomorphic analysis. We also
present the stormwater management plan for Fishpot Creek based on that
analysis. Briefly, the Fishpot Creek watershed encompasses 10.5 square miles
in western St. Louis County. Fishpot Creek is an Ozark Plateau stream flowing
through Mississippian Limestone with extensive chert lenses. The stream is
highly bedrock controlled and the alluvial, colluvial and residual soils are clay-rich
and relatively resistant to erosion. The flow regime in Fishpot has been replaced
with extremely abrupt, flashy flows. The basin has experienced intensive urban
development much of which occurred without measures to manage either the
quantity or quality of stormwater generated. The 25 mile stream is highly
manipulated; much of the riparian corridor has been eliminated and structures
are commonly located at the edge of the stream bank.
Given the degree of damage to the stream system and the restrictions placed by
existing structures, the potential for restoration is limited. However, the plan
presented in this report protects property and infrastructure from flood and
erosion hazard while restoring some of the natural functions of the creek. This
approach integrates civil and geological engineering with fluvial geomorphology;
it reflects the state of current practice in river engineering. In river engineering
terms, restoring stream function explicitly includes both biological and physical
integrity.
Neither this report nor the Fishpot Creek SSMIP that preceded it is a watershed
management plan. By definition, any plan intended to guide decision-making on
a watershed scale must place land use on an equal footing with channel
management. While both reports acknowledge changes in land use over time
and the effect of land use changes on stream flows, neither addresses major
recommendations for proactively managing the progress of precipitation to
surface and groundwater. A true watershed management plan would outline
methods for limiting stormwater damage through the following mechanisms:
1. Discouraging further development in flood-vulnerable areas
2. Where possible, removing structures from floodplains
3. Development practices that reduce the quantity and protect the quality of
runoff
4. Protection of intact forest, wetland and native grassland areas.
Comprehensive watershed plans require considerable political and social
commitment, as well as a broad range of technical expertise. Some of the most
interesting and far-reaching watershed initiatives occur in Massachusetts where
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both the quantity and quality of stormwater runoff are managed. The regulations
require preservation of pre-development hydrology. Treatment of stormwater
runoff is required and concentration of flows is strongly discouraged (MA Dept. of
Environmental Protection, 1997). Sustainable community plans such as those
throughout Virginia and Maryland (Center for Watershed Protection, 1999, 2000)
describe land use practices that protect both terrestrial and aquatic resources
while accommodating development. The Virginia guidelines for low impact
development are based on 22 model principles most of which reduce impervious
surfaces and explicitly provide for protection of forest, meadow, wetland and
stream resources. The communities adopt these practices for clear tangible
benefits. These include smaller loads of stormwater pollutants, increased
property values, reduced development costs, reduced regulatory compliance cost
and protection of natural resources.
Few communities in our region have been able to apply watershed management.
Although in recent years, many cities and agencies have begun to reduce their
reliance on site-specific repairs in favor of more systemic approaches. In the
Kansas City area, the Mid America Area Regional Council (MARC) has
commissioned a revision of its stormwater regulations. The revised regulations
are derived from a governing principle known as Q2. Q2 refers to Quantity and
Quality, meaning that stormwater will be managed in such a way as to avoid
increases in peak flows and to maintain or enhance the quality of receiving
waters. The regulations will result in protection of headwaters streams, riparian
corridors and use of fluvial geomorphic principles in stream intervention.
2.2 Organization of the Report
This report includes a review of the existing stream conditions and the driving
forces for instability. Detailed information regarding fluvial process, channel
geometry and rationale for management recommendations is included. The
report provides some perspective on the progression of channel instability
problems if left untreated. The recommendations address flood conveyance,
erosion, deposition, systemic stream stability and water quality.
In the FUNDAMENTALS OF FLUVIAL GEOMORPHOLOGY section, we present
an overview of stream mechanics with particular emphasis on how streams
respond to urbanization. This section also demonstrates why practices such as
hard armoring and channelization intended to prevent flooding and erosion so
often have precisely the opposite consequences. The METHODOLOGY section
includes brief descriptions of the major types of data gathered, its purpose and
how data is analyzed. METHODS OF MANAGEMENT outlines established
methods in river engineering that support safe and sustainable streams. These
methods are materially different from conventional civil approaches in their
emphasis on achieving multiple functions such as flow conveyance, sediment
transport competence (and thereby erosion protection), water quality, wildlife
2-3
habitat and aesthetics. All of the recommendations in this report are grounded in
river engineering and reflect the approaches and values described in this section.
In RESULTS, we present our assessment of the stream’s physical condition. We
address the influence of past disturbance on current condition and the likely
progression of the existing instability. This section includes summaries of
geomorphic observations for each reach including an analysis of major
geomorphologic processes and features.
In the RATIONALE FOR PROJECT PRIORITIES we describe our method of
selecting treatment sites. We do not recommend a traditional cost-benefit model
because of its inherent dependence on spot repairs that simply shift the problem
elsewhere and further destabilize the system. Instead we recommend a system
in which actions with material influence on the stability of the stream overall take
precedence over local repairs.
In PROPOSED INTERVENTIONS, we present a series of recommendations for
sustainable management of Fishpot Creek. We have addressed each SSMIP
recommendation with an intervention or management strategy that not only
addresses the local flooding or erosion concern, but maintains systemic stream
stability and sediment transport competency in the watershed. The explicit
purpose of our recommendations is to prevent relocation or aggravation of
stability problems elsewhere in the watershed.
The PROJECT COST section details the rationale and assumptions used in the
cost estimates as well as the cost of design and construction of each major
recommendation. All major recommendations are presented with their location,
priority, brief description of the recommended treatment and cost in the MASTER
PROJECT TABLES.
COMPARISON BETWEEN 319 PROJECT MASTER LIST AND SSMIP
PROJECTS includes a point by point evaluation of recommendations presented
in the Fishpot Creek Watershed SSMIP in light of the new information provided
by the geomorphic analysis. In this section we describe where and how capital
improvement projects in the SSMIP have a high likelihood of unintended adverse
consequences and we provide a more sustainable solution.
A chapter entitled CONCLUSIONS AND IMPLICATIONS FOR FUTURE
MANAGEMENT completes the body of this report.
We present more detailed background information in the APPENDICES. All of
the data used to generate the recommendations are included in the
geomorphology report, detailed reach descriptions, survey data and project
photographs. We provide detailed spreadsheets of opinion of probable cost for
each recommendation. A glossary of terms commonly used in geomorphology
and river engineering and a brief overview of common conservation stormwater
techniques are also included.
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3.0 FUNDAMENTALS OF FLUVIAL GEOMORPHOLOGY
3.1 Brief History of Stormwater Management
The overriding principle of stormwater management in our region is to
concentrate and convey runoff away from populated areas. The historical
approach of concentrating water flows made sense when streams were the
primary means of waste disposal. In this case, protecting the public from disease
took precedence over other considerations. Unfortunately even as the
engineering community developed better methods of sewage collection and
disease control, stormwater methods singularly promoting conveyance persisted.
However, as the costs of urban stormwater damage escalated, communities
have sought more effective ways to manage the problem. As a result,
stormwater practices have slowly progressed from the purely reactive to early
attempts at watershed-scale management.
The advent of watershed-scale hydrologic and hydraulic modeling represents a
quantum improvement in stormwater management. Modeling can approximate
the increase in runoff associated with new development and estimate the
cumulative increases in flood volume. Moreover, the ability to predict flows
throughout the basin constitutes one of the critical elements of truly systematic
stormwater management.
Hydrologic and hydraulic models are powerful and useful tools for stream
management. However, their utility is limited by the assumptions underlying the
models and the scale on which they are applied.
Hydraulic models are designed to predict water surface elevation at a series of
points as a function of flow rate, channel slope and channel roughness. The
models are intended to predict these elevations under a set of narrowly defined
conditions. It is important to be aware of these conditions when examining the
results of a model. For example, a model designed for the sole purpose of
predicting the flood elevation for the one percent flow will not predict the flood
elevation for smaller flows with any accuracy or consistency. Because virtually all
processes in the physical world are so complex, mathematical models contain
simplifying assumptions. We make assumptions about those phenomena that
we do not fully understand or are so complex that incorporating them into the
model would render it too unwieldy to be useful.
The assumptions for the common hydraulic models are that the stream
boundaries are fixed and that there are smooth transitions in shape and flow rate
from one section of the model to the next. These models also assume that the
stream carries no sediment. In other words, the models are based on the
assumption that streams are not self-forming. These assumptions are reasonably
valid for canals. While major rivers certainly carry sediment and have movable
boundaries, the boundary effects are small relative to the size of the channel and
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the models perform well. However, in smaller rivers and streams, the magnitude
of channel adjustment relative to the size of the stream and the influence of
sediment transport are much more significant. In streams, the predictive power of
most common hydraulic models is compromised by this violation of fundamental
assumptions. This does not mean that hydraulic models are not critically
important; they are. However, it is equally important to understand their
limitations and to gather other information to address these deficiencies. By
adding detailed information about the geomorphology of the stream, its sediment
transport competency and the likely form and rate of stream adjustment, we can
more thoroughly understand the effects of proposed interventions on systemic
stream stability.
The next step in stormwater management evolution is the inclusion of rigorous
stream analysis. Nearly all of us have the compatible goals of safe stable
streams and clean water with abundant wildlife. Protecting property and
protecting the natural resource are not mutually exclusive. Fortunately, there is
now a strong consensus among professionals about basic stream mechanics
and functions. Over the past 30 years, we have seen a convergence of technical
understanding involving fluvial geomorphology, geology, hydraulic and hydrologic
engineering and the life sciences (USACE 1989, 1993, 1994). Many of these
advances are documented in USACE Engineering Design Manuals and reports
(USACE, 2001). We now have a defensible methodology for managing streams
that protects both people and the stream.
3.2 How Streams and Rivers Work
The three functions of a river system are the collection of water and sediment,
the transport of these materials and deposition. The classical concept of a river
system or watershed is shown in Figure 3.2.0. Erosion occurs in the youth stage
at the headwaters; along the mature stage in the mid section, the river transports
the water and sediment. At the old stage, the river deposits water and sediment
at its mouth. In Fishpot Creek, this sequence occurs from the headwaters
through its confluence with the Meramec River.
Upper Watershed
New
(Erosion)
Lower Watershed
Mature
(Transport)
Old
(Deposition)
Figure 3.2.0 Stages of a river system (adapted from Rieneck and Singh, 1980).
3-2
As shown on Figure 3.2.1, the profile of the channel slope for a watershed
becomes flatter proceeding downstream. Along the steepest portion, the process
is dominated by erosion, and along the flattest portion, it is dominated by
deposition.
Upper Watershed
Lower Watershed
Erosion
Transport
Deposition
Figure 3.2.1 General channel profile of a watershed.
This concept of the large watershed is also applicable to a smaller scale. For
example, a dammed river can act as the end of a watershed, where sediment
and water is deposited and the sequence of river formation is reset downstream
(Figure 3.2.2). In this case the lake acts as the receiving waters and the outfall
behaves like a spring beginning the next watershed. Stream crossings such as
bridges and culverts can also reset river formation, as shown on Figure 3.2.3. In
urban settings the characteristic profile shape of natural watersheds may be
repeated after each hard crossing that materially affects transport of water and
sediment. These obstructions may geomorphically isolate the reach. These
channel profiles occurred along several segments of Fishpot Creek main stem
and its tributaries.
Deposition
Transport
Erosion
Deposition
Transport
Erosion
Dam
And
Reservoir
Figure 3.2.2 Effect of a dam resetting the stream formation sequence
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Deposition
Transport
Erosion
Deposition
Erosion
Transport
Bridge
Deposition
Transport
Culvert
Erosion
Deposition
Transport
Erosion
Bridge
Figure 3.2.3 Effect of stream crossings resetting the stream formation
sequences.
Fundamentals of River Mechanics
Streams are Self Forming. The primary feature of urban stormwater is the
accelerated delivery of concentrated runoff. This produces stream responses
that were unappreciated until recently. Before proceeding with details of the
Fishpot Creek Watershed, it is useful to consider the fundamentals of stream
mechanics in light of both urbanization and the resulting attempts to manage
urban streams. The accelerated runoff is a consequence of increased impervious
surface and the simultaneous increase in drainage network density. While this
fact has long been understood, the consequences have not. Specifically, the
inevitable response of neighboring streams to the increased runoff is both more
consequential and more complex than previously understood.
The modern incarnation of stream management began in the 1950s when the
significance of stream mechanics for stormwater management became clear.
Streams exist in a state of dynamic equilibrium in which the driving forces for
channel form are balanced by the resisting forces. The driving forces are the
quantity of water and sediment delivered through a stream while the resisting
forces are the strength and roughness of the channel materials and the channel
shape. When the driving forces exceed the resisting forces, the stress applied by
water or sediment exceeds the channel strength and erosion occurs.
Conversely, when resisting forces exceed the driving forces, the channel may
build through deposition of sediment. The stream channel responds by altering
its shape in plan, profile and cross-section to accommodate the changes in flow
volume and applied shear.
3-4
The pattern of channel evolution in response to a disturbance is depicted in
Figure 3.2.4 (page 3-11). Channel adjustment is a consequence of the selfforming and self-maintaining capacity of all rivers. Lane’s Relationship (Lane,
1955), expresses this proportionality between driving and resisting forces.
QS D50
Where QS
D50
S
QW
∝
S QW
≡ Quantity of sediment
≡ Median size of mobile particles
≡ Slope of the channel bed
≡ Quantity of water
From this relationship it is clear that a change in any of these parameters
precipitates the change in one or more of the others. One example is the typical
increase in Qw associated with urban development. The response to this
increase is some combination of the following: a decrease in channel bed slope
through down cutting (incision), an increase in sediment load (increased erosion)
and an increase in the median size of mobile particles.
Table 3.2.0 on the following page illustrates the potential outcomes of changing
sediment and water quantities while holding slope and median particle size
constant.
3-5
Water
Quantity
Change
Sediment
Quantity
Change
(∆
∆ QS )
+
−
(∆
∆QW)
+
−
No change
+
No change
−
+
No change
−
No change
−
+
+
−
Outcome
Increased Rate of Channel Adjustment*
Decreased Rate of Channel Adjustment
Sediment Accumulation
Wider and Shallower Unstable Channel*
Incision
Narrower and Deeper Unstable Channel*
Incision
Wider and Deeper Unstable Channel*
Sediment Accumulation
Narrower and Shallower Unstable Channel
Sediment Accumulation*
Incision
Deeper and Possibly Wider Unstable Channel
Table 3.2.0: Response to changes in water and sediment quantity (adapted from
Schumm 1977).
The responses observed in the Fishpot Creek Watershed are marked with an “*”.
The more erosive responses such as incision and widening most often occur in
the upper and middle portions of the watershed. Sediment accumulation is more
common in the middle and lower portions of the watershed.
When considering all four parameters, these responses often occur in sequence.
The following examples illustrate:
•
Initial change: QW ↑; response: QS↑. Often the bed slope remains
relatively unchanged at first, so to maintain the proportionality, Qs
increases. The increase in sediment load is generated by down cutting of
the channel bed (incision), scour of the stream banks or both. The
incision locally steepens the channel slope, compounding the driving force
for more erosion. This local steepening of bed slope is called a knick
point. Knick points migrate upstream liberating sediment as they
progress. On a larger scale, a knick zone includes several closely spaced
knick points. When the stream banks exceed their critical height, mass
failure ensues. This reconfiguring of the channel geometry continues until
the equilibrium described by Lane is re-established.
3-6
•
Initial change: QW ↑; response: D50 ↑. This condition occurs when there is
little sediment initially available in the bed or banks. So, to maintain Lane’s
proportionality, the size of the median mobile particles increases. Under
this condition, rock armor that previously protected a structure becomes
mobile as the D50 increases. Subsequently, the service life of the
infrastructure declines. The natural bed armoring aggregate, previously
mobile only during less frequent floods, becomes mobile during more
frequent events. Consequently, the underlying, more erosion-prone bed
and bank materials are exposed to greater and more frequent erosive
force.
•
Initial change: QW ↑; response: S ↓. If the channel bed is relatively
resistant to incision, the stream may respond to increased flows by
decreasing its slope. The stream accomplishes this decrease in slope by
meandering or increasing the channel length over the same change in
elevation. The downstream progression of point bars (crescent-shaped
sediment deposited on the inside bank of stream bends) opposite the
downstream progression of eroding and failing cut banks (steeper outside
banks of stream bends) are classic signs of meandering.
•
Initial change: S ↑; response: QS ↑. Increasing channel slope is often
accomplished through channel straightening to achieve greater flood
conveyance or to optimize land development. This increase in slope
invariably causes an increase in sediment load, in mobile D50 size or both.
Bed and banks erode to generate the sediment that deposits downstream
where channel slopes are flatter. The effective change in water surface
slope may extend upstream well beyond the actual channel straightening,
extending the accelerated erosion. The sediment eroded from upstream
of the channelization and deposited downstream counteracts the effect of
the channelization and improvements in flood conveyance are often less
than anticipated.
Schumm (1969) expanded on Lane’s proportionality by including flow depth (D)
and width (W). The following Table 3.2.1 presents the interactions between
these parameters. The examples of change marked with an “†” are ones
occurring in the Fishpot Creek watershed.
3-7
Flow
Depth
Change
(∆
∆D)
Flow
Width
Change
(∆
∆W)
-
Median
Mobile
Particle
Size
Change
(∆
∆D50)
+
+
+
-
+
+
+
+
+
+
+
+
U
U
+
Sediment
Quantity
Change
(∆
∆QS)
Water
Quantity
Change
(∆
∆QW)
Channel
Slope
Change
(∆
∆S)
+
++
--
+
+
+
+
-
+
-
U
U
U
U
U
+
-
++
+
+
-
-
+
--
+
+
+
+
-
-
U
-
+
+
Examples of Change*
Long-term effect of urbanization†;
Increased frequency and magnitude of peak discharge;
Channel erosion
Intensification of vegetative cover through forestation and
improved land management reduces sediment flows
Diversion of water into a stream
Increased frequency and magnitude of discharge from lined
reach upstream†
Parallel changes of water and sediment discharge with
unpredictable changes of slope, depth and bed material†
Land-use change from forest to crop production or
urbanization†;
Sediment discharge increasing more rapidly than water
discharge;
Bed changes from gravel to sand, wider shallower channels;
Larger bed and bank armoring becomes mobile, exposing
smaller particle sizes for transport†.
Removal of water from the stream resulting in a narrower
channel
Increased sediment supply and constant or reduced water
discharge
U: Unpredictable
* Examples presented in italics are based on observations by Intuition & Logic
Table 3.2.1 Potential effects of changing flow and geometry parameters on channel stability adapted from Schumm,
1969.
3-8
Energy Management in Streams
Stable streams are dynamic. To maintain dynamic equilibrium, in response to
changes in their watersheds, streams adjust their shape in plan, section and
profile. When considering streams from a management perspective, it is
especially important to note that streams trend toward this equilibrium condition.
Channel Evolution in Cross-Section. The process by which streams achieve
these adjustments has been described by Schumm and others (1984) and more
recently Simon (1989). The evolution of channel morphology can be described in
six stages: I) Pre-disturbance, II) Disturbance, III) Incision, IV) Widening, V)
Deposition, and VI) Recovery and Reconstruction.
At Stage I, the channel is functioning in its natural stable state often with bankfull
floodplains positioned along the low flow channel. While streams can be stable
without these internal elements, bankfull floodplains are a common feature of
many stable streams, particularly in the Midwest. Bankfull floodplains occur at
the elevation corresponding to the dominant discharge. The dominant discharge
is the flow that, over time, accomplishes the most work on the stream channel. In
undisturbed streams, the dominant discharge typically occurs every 1.5 to two
years. The bankfull floodplain performs an invaluable function of lowering the
bank shear during higher flows and effectively managing the stream energy.
Most of the work done by streams is performed by more frequent flows rather
than the major flows, such as a 100-year flood. The analogy of moving a shovel
full of sediment every day for a year compared to moving a wheel barrow full of
sediment once a year illustrates this concept of stream forming flow.
During Stage II, natural or manmade events disturb the channel.
Characteristically, disturbance eliminates the two-stage channel and may include
removal of woody riparian vegetation along the banks. Common forms of
manipulation include channel straightening, relocation or widening of the channel
into a trapezoidal shape. In the past, these methods were often perceived as the
solutions to handling increased peak flows.
In Stage III, the stream cuts downward to lower its channel slope to redistribute
energy. This incision process migrates upstream. The migrating face of an
incision front is referred to as a knick point or knick zone. The typical shape of
these channels is V- shaped to narrow U-shaped. In soils such as loess and siltrich alluvium, incision may proceed rapidly. Knick point migration rates
exceeding 1000 feet/year are not uncommon in the Central Midwest. Often
stream side residents do not complain about incision because local flooding
problems are temporarily reduced as the channel incises deeper. Incision
proceeds until the channel reaches a stable slope, the incision reaches a more
resistant layer or the stream banks begin failing because of mass wasting.
3-9
Channel widening through mass wasting of the stream banks, Stage IV, follows
incision. There are two common mechanisms of bank failure. Fluvial action
erodes soil away from the toe of the slope resulting in a cantilevered bank, which
eventually fails through toppling. Alternatively, the incision cuts deeply enough
into the bed that the stream banks exceed their critical height and fail. Both
mechanisms may operate in a stream. During this stage, the complaints of
nearby residents rise because of the increase in bank failures.
The consequences of incision and subsequent channel widening on aquatic biota
can be severe. Active incision may limit local migration of fish and the bed
disturbance eliminates the stable, heterogeneous bed forms necessary for
spawning, feeding and shelter. The release of excess sediment also interferes
with predation and respiration. When the riparian corridor is lost during widening,
the stream loses shade, becoming hotter and with lower dissolved oxygen
concentrations.
The next phase of channel evolution, Stage V, occurs when the channel has
sufficiently widened and begun depositing sediment eroded from upstream
reaches in the watershed. This is also the phase when culverts and bridge
openings become partially filled. This occurs most often when the culvert or
bridge opening was over-widened to accommodate a single design flow. The
sediment is deposited to an elevation corresponding to the dominant discharge.
In Stage VI, the channel regains the equilibrium condition and efficiently
transports both water and sediment. If a substantial increase in Qw precipitated
the adjustment, final dimensions of the channel will probably be larger than the
pre-disturbance condition; however, the basic shape will be similar. During this
stage, the riparian vegetation and a stable bed form re-establish. In the absence
of chemical pollutants, water quality also improves during this phase. We have
noted the return of aquatic life to St. Louis area streams even after severe insult
once the channel adjustment has run its course.
Each of these phases is depicted in the following Figure 3.2.4.
3-10
Stage I Pre-disturbance
• Bed and bank materials balanced with
erosive forces
• Permanent woody vegetation near the
water line
• Two-stage channel shape evident at
about 1.8 year return interval
Stage II Disturbance
• Channel altered to
accommodate a single purpose
• Removal of permanent woody
vegetation near the water line
• Two-stage channel shape
eliminated
Stage III Incision
• Widespread bank failures as banks
exceed critical height
• Lost or perched bankfull floodplains
• “U” shaped channel- poor habitat
• Woody vegetation high on bank with
many “surfer” trees
Figure 3.2.4 Channel Evolution Model (from Simon, 1989)
3-11
Stage IV Channel Widening
• Channel adjusts to new flow regime
• Over-steepened banks fail to stable
shape- sediment in channel may impair
water quality and aquatic habitat
• Widespread complaints from property
owners
• Ineffective bank armoring or dumping
Stage V Deposition
• Deposition begins from liberated
sediment
• Vegetation establishes near water
line
Stage VI Recovery and Reconstruction
• Bankfull floodplains reconstructed
from liberated sediment
• Woody vegetation establishes near
water line
• Stability re-established
• Aquatic life may return
Figure 3.2.4 Channel Evolution Model (cont.)
3-12
Channel Adjustment in Plan Form; Meander Formation and Migration. So far,
our discussion has focused primarily on adjustments in channel cross-section
and slope. Adjustments in plan form are as common and have a similarly
important influence on the sustainability of a stormwater system and on the
safety and service life of near-stream infrastructure.
Straight stream channels are rare and require a narrow set of circumstances to
maintain dynamic equilibrium in a natural setting. Leopold (1964) suggested
that straight channels in nature never exceeded a length of 10 channel widths.
The near-universal tendency for stream channels to flow in a sinuous plan form
has been theoretically and empirically investigated for decades (Leopold and
Langbein, 1969, Williams, 1986). Like all other open systems, streams adjust
their form to minimize the expenditure of energy. The formation of pool-riffle
patterns and meanders are consistent with this trend towards maintaining an
equilibrium condition.
Meanders are complex in both formation and behavior. The following
paragraphs summarize how meanders develop, why they migrate downstream
and how meanders re-establish after streams are artificially straightened.
Meander formation graphically demonstrates the principle of perturbation and
response (the familiar cause and effect) in stream mechanics. The perturbation
is the force applied by moving water and sediment and the response is the shape
of stream channel.
Details of the meander genesis are still under investigation, particularly for nonalluvial systems. To describe the basic process of meander formation, the
distinction between the meander flow or discharge centerline and the channel
centerline is important. As illustrated in Figure 3.2.5, the channel centerline
(response) lags the discharge flowline (perturbation). The flow in a stream does
not progress in straight lines parallel to the stream channel. Rather the flow is
comprised of a primary flow oriented downstream and transverse flows oriented
perpendicular to the primary flow.
Along the discharge flow path, these inward and outward transverse flows are
balanced. However, along the channel flow path, there is considerable
asymmetry. Because of the variable turbulence and secondary flow patterns,
the flow velocity, sediment transport and boundary shear stress are non-uniform
across the channel. These areas of turbulence produce alternating pulses of
sediment scour and deposition.
3-13
Flow
Channel centerline
Discharge centerline
Figure 3.2.5. Discharge centerline in relation to channel centerline.
Areas of scour and deposition alternate along the axis of discharge flow
producing a pool along the outer bend and a corresponding point bar on the inner
bend. As the pattern of scour and deposition alternates from one side of the
channel to the other, the thalweg (deepest portion of the channel cross section)
and maximum flow velocity cross over the center of the channel. These cross
over points become the riffles. The alternating pattern of bar building and bank
scour causes straight streams to evolve into meandering ones with a sinuous
pattern. Specifically, this is how channelized reaches eventually reacquire their
previous sinuous shape.
Although the process of creating riffles and pools encompasses highly variable
processes, the riffles and pools occur at regular and predictable intervals. The
spacing of these riffles or pools along the thalweg relates closely to the width of
the stream at the elevation of dominant discharge. This links riffle and pool
locations to the perturbation and response of channel form. Figure 3.2.6
illustrates riffle geometry in plan form. The spacing of the pools, which are near
the outside bend and slightly downstream of the maximum curvature of the
meander, have essentially the same relationship to channel width as the riffles.
Z
L = 4πW
Rc/ W = 2 – 5
Riffle spacing (Z) = 2πW
L
Rc
W
A
L = wavelength
A = amplitude
Rc = radius of curvature
W = width at dominant discharge
Figure 3.2.6. Meander Geometries
3-14
In alluvial streams of homogeneous material, meanders take the form of sinegenerated curves. Leopold and Langbein (1969) demonstrated that this shape is
the most hydraulically efficient form for turning water. Chang (1998) presents a
more analytical assessment of this meander plan geometry. These relationships
between stream width, riffle spacing, meander wavelength and radius of
curvature are remarkably consistent for streams and rivers throughout the world.
Most stable relationships in channel geometry include the channel width at the
elevation corresponding to the dominant discharge. Riffle spacing (Z) generally
occurs every 6.3 bank widths (W) where W is the width at the dominant
discharge. Not coincidentally, this is spacing is essentially 2πW. Meander
wavelength is approximately 12 bank widths, which approaches 4πw. These
general relationships also apply to meanders formed by melt waters through
glaciers and the Gulf Stream current in the ocean (Leopold and Langbein, 1969).
The radius of curvature is also related to the channel width at dominant
discharge elevation. The ratio of meander radius of curvature (Rc) to channel
width (W) generally ranges between two and five. Bagnold’s (1960) investigation
of energy losses at bends confirmed the empirical observations by determining
that flow energy losses are minimized through this shape. A tighter radius
causes a flow separation and severe energy losses, a hydraulic inefficiency that
is not persistent. In natural rivers, channel bends erode to a Rc/W ratio of 2-5
and then maintain that form. This indicates that the hydraulic efficiency is
optimized by this form. By contrast, the correlation of meander amplitude to the
other channel and meander geometries is less well understood. Meander
amplitude correlates poorly with the dominant discharge width.
In streams containing heterogeneous media and in confined channels, the
meander pattern is interrupted by variations in bank structure, infrastructure,
confluences, geologic features and channel manipulation. Moreover, streams
out of equilibrium also display distortions in meander pattern and growth.
Streams in most urban areas exhibit all of these characteristics, particularly in the
more disturbed streams. Nevertheless, the fundamental relationships describing
these patterns remain broadly applicable.
Meander Migration. Streams can migrate both laterally and downvalley. While
meander amplitudes can subside, the primary concern for most watershed
managers is an increase in meander amplitude. The apex of the meander bend
is rarely symmetrical and tends to skew downstream. As is the case of meander
formation, the asymmetry of flow velocities strongly influences meander
progression laterally and downstream. All of the processes that drive the
formation of meanders remain active in the migration of meanders. As discussed
previously, the discharge flow path (meander path) and the channel centerline
are out of phase. The channel centerline lags the flow path because the channel
formation is the feedback in response to the flow pattern. So the point of
3-15
maximum flow curvature is slightly downstream of the point of maximum channel
curvature. Therefore, the boundary shear stress is highest slightly downstream of
the bend apex. When the shear stress at this point exceeds the resistance of the
bank, failure ensues and the eroded bank material migrates downstream to
deposit in the subsequent point bar.
Influence of Hard Points and Resistant Structures on Meander Migration.
Sometimes meander bends migrate against a resistant feature such as a rock
outcrop, strong clay layer or man-made wall. Some of the consequences are
outlined below (see Figures 3.2.7
through 3.2.9).
Hard
point
• Case 1: Hard point length is short
relative to meander bend length;
flanking case: In the short term,
the rate of bank retreat slows at
the hard point (Figure 3.2.7). The
bank upstream of the hard
Figure 3.2.7
feature continues to retreat
Meander adjacent to
(Figure 3.2.8a). This increases
resistant structure
local turbulence and induces
stronger local secondary currents
(Thorne et al, 1997). This in turn
increases scour of the surrounding less resistant materials and usually
causes the flanking of the hard point (Figure 3.2.8b).
•
Case 2: Hard point length is short relative to meander bend length: bend
deflection case: When the hard point is too resistant to be flanked, the
channel may deform more sharply and the degree of bank retreat
upstream of the hard point becomes exaggerated. Or, the stream may
form a cut-off chute to the convex side of the channel.
•
Case 3: Resistant structure length is long relative to meander bend length:
In this case the deformation of the bend can be extreme as is often the
Hard
point
Figure 3.2.8b
Hard point flanking
Figure 3.2.8a
Meander advance
3-16
case of a structure downstream of the meander apex. The downstream
limb is fixed while the upstream limb advances down valley (Thorne et al,
1997). If flow is directed to adjacent softer material, the stream may
develop exaggerated meanders that eventually cut off (Figure 3.2.9).
•
Hard
point
Figure 3.2.9
Meander distortion around
extended resistant layer
3-17
When migrating bends
encounter extensive resistant
features such as longer rock
outcrops or long gabion walls,
deep scour pools develop
along the resistant bank. The
energy of the moving water
can no longer be expended by
modifying the stream’s shape
in plan-form. The energy is
dissipated by the changes in
longitudinal profile and cross
section.
4.0 METHODOLOGY
Before beginning any design project involving a stream or river, it is critical to
understand the stream dynamics. This allows the designer to properly assess
the likely response of the stream to the proposed action. Both the professional
river engineering literature (Thorne et al, 1997, Thorne, 1998) and the US Army
Corps of Engineers (USACE, 2001) describe generally accepted methods of
evaluating stream and river stability. The most notable procedures are briefly
described below.
4.1 Background Data Analysis
This phase of analysis includes examination of the terrestrial and fluvial features
of the watershed. It includes analyses of drainage network features such as
network density, homogeneity, angularity and degree of geologic control. Data
sources included current and historical maps, reports and articles, aerial
photographs and GIS information (Benham, 1982). Aerial photos often provide
the basis for comparing the current hydrologic regime with the flow regimes of
the past. Methods of aerial photointerpretation for this study were in general
compliance with those described by Lueder (1959). Historical aerial photo
interpretation yields important information about the dominant process active in
the stream over several decades. With careful examination, processes such as
incision, deposition and meander advance can be inferred.
The purpose of this historic analysis is to understand how the watershed
distributes precipitation, transports water and sediment and, most importantly for
urban streams, responds to man-made changes. The influence of vegetation,
run-off distribution and presence of geologic controls may become apparent in
this phase of analysis. Through this process, we gain insight into the
responsiveness of the stream system.
Understanding how a stream will respond to a change in its watershed is
necessary to the design of a stabilizing treatment. Throughout the Fishpot Creek
watershed, bedrock control limits incision in response to increased flows. For
these streams, widening becomes the more pronounced response. Conversely,
streams incise rapidly and often deeply through loess or silty alluvium. In alluvial
streams, widening due to streambank failure is a consequence of incision.
Once the basic watershed characteristics are understood, the examination of
man-made changes and their effect on stream behavior becomes more accurate.
When evaluated over several decades, sequential channel “improvements” have
consequences on stream behavior that indicate the relative robustness or
sensitivity of each stream. For example, determining the timing and extent of a
disturbance such as past channelization helps us predict the stream’s response
to current treatments. Further, anecdotal evidence from streamside property
4-1
owners may corroborate the broad predictions of the basic landform and
drainage network analysis.
This phase of analysis often raises issues requiring more detailed assessment in
the field.
4.2 Field Investigations
The field investigation confirms or refutes the preliminary findings of the
background data analysis and provides enough hard evidence to establish the
condition of the stream at a systemic level. Field investigations should be
performed by experienced professionals with expertise in geomorphology,
hydraulics and hydrology, geology and biology.
The longitudinal (long) profile is among the more important diagnostic methods in
fluvial geomorphology. This survey is accomplished by traversing the channel
and surveying the elevation of the thalweg profile. In addition to surveying
thalweg and water surface elevations, a complete long profile includes elevations
of the lower limit of woody vegetation, potential bank full floodplains and
abandoned terraces. Pool-riffle spacing and the location of bedrock outcrops can
also be determined at this point.
Field investigators measure channel cross-section geometry throughout the
project reaches. The frequency with which sections are measured is dependent
on the rate at which the cross-section varies along the reach and perhaps on the
level of the analysis. In any case, cross-sections are measured at each
significant change in shape, at representative pools, runs and riffles and at each
bridge, culvert and other structure. Cross-section measurements should be
detailed enough to detect each significant break in slope. Scour or trash lines,
abandoned terraces and potential bankfull floodplains/dominant discharge
indicators (i.e. change in bank slope) should be clearly identified. There should
be sufficient cross-sections to support determination of process and process
change throughout the reach.
Documentation of bed and bank materials and their distribution through the
project reach informs assessments of channel and future resistance to erosion.
At a minimum, the data gathered includes a qualitative description of
stratigraphy.
Much of the information used in plan form meander analysis comes from
topographic surveys and aerial photographs. Visual evidence in the field of
advancing or receding bars and bank scour patterns are diagnostic features of
meander advance.
4-2
The degree of instability and the progress towards recovery can be assessed
using field indications of previous instability. These include “surfed” trees, slope
failure scarps and bulging toes, and freshly exposed or barked-over tree roots.
Vegetative characteristics include the quality, size and structure of the riparian
forest, percent of canopy cover and presence or absence of invasive species.
Dominant and sub-dominant species and the successional status are also
important. From this information the investigator infers the timing and degree of
disturbance as well as the stream’s state of recovery. Sudden changes in
vegetation type often accompany localized problems, which helps distinguish
between systemic and local concerns. Vegetative status also indicates how well
the stream banks will respond to soil biostabilization and provides insight into the
potential for habitat recovery.
Field professionals also gather data regarding recurring flows for comparison
with the hydraulic model. Scour lines, lower limit of woody vegetation and
elevation of bank full floodplains are important indicators of frequent flow
characteristics that are often unavailable or inaccurately described in hydraulic
models.
In streams with a strong bedrock control such as Fishpot Creek, the field data
also included measurement and GPS location of joint set attitudes and bedding
planes. The bedrock joint orientation data were compiled and analyzed through
statistical compilation and stereonet plots. The trends of lineal orientation in
Fishpot Creek and its tributaries were determined by measuring orientation
trends from USGS 7.5-minute Quadrangle Maps and historic aerial photographs.
Both data sets were compared to determine to what degree the bedrock geology
affects the behavior of the creek and its tributaries.
The final major data element is sediment transport, an often overlooked but
critically important stream process. The competence of the stream to carry its
sediment load strongly influences both flooding and erosion. In the simplest
terms, a stable stream will transport the sediment load delivered to it without
scouring its bed. If the stream has insufficient transport competence, the channel
bed will aggrade and flood elevations may rise. Conversely, if the stream has
excess transport capacity (driving forces are greater than resisting forces), it will
scour the channel bed and banks.
In field investigations, this transport competence is often interpreted from
imbrication of coarse sediment, sorting of bed material on bars (generally coarse
to fine proceeding downstream), pattern of bar placement, and size and shape of
sediment ripples and dunes. Sediment features, such as center bars in a
historically single thread stream, generally indicate inadequate transport capacity
relative to the material supplied to the reach. These features are often
associated with a large sediment influx delivered to a previously stable reach or
an actively meandering system.
4-3
Because movement of coarse sediment has such a strong influence on both
flooding and erosion within the Fishpot Creek watershed, the data collection
included measurement of sediment transport indicators. Gravel/cobble sequence
data was collected for over 15,000 feet of channel, from the Hanna Road Bridge
to the Wren Avenue triple box culvert. Position and length of each cobble bed
segment was recorded using a hand-held GPS unit. Channel width was
measured, along with the right descending bank and left descending bank height
for each GPS waypoint that was set. All data gathered in the field was then
entered into a spreadsheet that calculated the average channel width, verses the
average length of each of the cobble riffles, and the average wavelength from the
beginning of one cobble reach to the end of the next.
4.3 Integration of Stream Stability Analysis Into Design
The interpretation of background and field data involves the multiple disciplines
of fluvial geomorphology, hydraulics and hydrology engineering, geology, civil
engineering, and soil bioengineering. In well-developed analyses the
assessments of each of these disciplines converge to a common conclusion of
stream process.
4.3.1. Channel Plan-Form. Channel plan form is compared to that of previous
years in terms of location, sinuosity and evidence of previous adjustment. In
sinuous reaches, the design team evaluates meander wavelength, pool-riffle
spacing, radius of curvature and amplitude in terms of their relationship to the
channel width at dominant discharge and sinuosity for the present and in many
cases past stream forms. The determination of meander geometry is further
refined with field observations of plan form adjustment such as advancing or
receding bars, bar shape and consolidation, and location and shape of erosion
features.
4.3.2. Channel Profile. The long profile is particularly useful for diagnosing and
locating incision. While the consequences of incision are often obvious from field
observations, determining the state of incision is usually more difficult. It is
critically important to distinguish between active incision and a previous incision
event that is no longer active; they require different treatment. The long profile
reveals sudden breaks in bed slope that signal a knick point and the subtler but
still recognizable change in slope over a distance indicating a knick zone.
The long profile depicts the bed slope. Correspondingly, boundary shear stress
and sediment transport capacity are directly proportional to slope. With slope,
hydraulic roughness and cross sectional area, the depth and velocity of water
flow are determined for selected precipitation events. Thus the long profile is
used to locate and determine the effect of changes in local and net slope on
stream process.
4-4
4.3.3. Hydraulic Data. Some hydraulic and hydrologic parameters are available
from the existing hydraulic model. This level of data is useful in assessing flood
capacity and potential backwater reaches. However, because the input to these
models include widely-spaced sections (over 500 feet) and generalized
roughness, slope and plan form, these parameters only generate broad
indications of stream functions during extreme events. These less frequent
events (i.e. 10 and 100-year events) occur when the system is inundated to the
point that internal channel characteristics are substantially submerged.
This level of analysis is limited when evaluating the more-frequent, dominant
events of water and sediment conveyance that form the stream or river. The
internal meanders and channel undulations that govern stream process during a
stream forming flow are glossed over in the macro-scale floodway models.
Therefore, even if the model were to use the stream forming flow, the input
geometry of the models is too vague to predict or accurately model stream
hydraulics.
Water and sediment flow are the two drivers in stream formation. Hydraulic data,
including hydraulic stress, is used for assessing flood capacity, evaluating
sediment transport competency and for corroborating assessments of channel
process. The energy grade line represents the kinetic and potential energy of the
system. Water surface profiles are used to understand effects on bridges, knick
points, obstructions and bank interventions. Backwater effects influence
decisions on lowering flood elevations and maintaining sediment transport
capacity. Often stream power (force applied over time) is determined from the
hydraulic model.
4-5
5.0 METHODS OF MANAGEMENT
The management recommendations in this report generally comply with the
principles of Natural Channel Design. This approach represents an integration of
fluvial geomorphology and civil engineering knowledge accumulated over the last
half century. Much of this work is documented in the Engineering Reports and
Manuals of the US Army Corps of Engineers (USACE 1994, 2001).
In Natural Channel Design, project objectives such as flood or erosion protection
are achieved by working with, rather than against, the forces shaping the stream.
Preservation of complex channel forms and the rich diversity of vegetation so
important to high quality stream ecosystems are central to this approach. In
contrast, the organizing principle of stormwater management in our region is
optimal conveyance for flood control coupled with symptomatic treatment of
erosion.
Over the past few decades, the science of stream mechanics and its applied
cousin, geomorphic engineering have advanced to the point where a different
organizing principle is technologically and economically practical. In a recent
report of the US Army Corps of Engineers (2001), the authors note that a change
in governing approach is unavoidable.
Mackin (1948) considered a shift to working with nature, rather than
against it, as the inevitable outcome of having to respond to the
undesirable consequences of channel modifications. Half a century
later, his foresight has proven true:
‘The engineer who alters natural equilibrium
relations by ... channel improvement measures will
often find that he has the bull by the tail and is
unable to let go - as he continues to correct or
suppress undesirable phases of the chain reaction
of the stream to the ‘initial stress’ he will necessarily
place increasing emphasis on study of the genetic
aspects of equilibrium in order that he may work
with rivers, rather than merely on them’.
A governing approach that acknowledges the self-forming nature of streams
begins by determining the cause of the instability before formulating a solution.
This includes defining the location and timing of the perturbations and the
subsequent responses. The background data review is critically important for
this phase. Coupled with field data regarding channel form and process, the
designer can reasonably assess whether a problem is local or systemic and if
systemic, whether the stream is approaching equilibrium or whether significant
adjustments have yet to occur. Only when the current condition and likely
progression of adjustment is determined, can the design team develop solutions
5-1
to address complaints and re-establish an equilibrium condition. In practical
terms, this requires designers to balance energy throughout the system rather
than to shift energy from one site to another. Balancing energy includes
managing the transitions between kinetic and potential energy, energy losses
and work. Effective designs match the energy grade line upstream and
downstream of the proposed treatment to prevent accelerated erosion and
deposition in the adjacent reaches. Sustainable designs also maintain sediment
transport competency throughout the system by managing the product of slope
and depth so that sediment is transported and excessive scour avoided.
Rivers balance driving and resisting forces in all three dimensions. When
working in the natural stream arena, the designer can shift the distribution of
applied stresses to achieve management objectives such as reduced bank
erosion. Stream bank erosion can be treated either by increasing the resisting
force of the bank, decreasing the applied force of the stream or both. Increasing
the shear resistance of a stream bank accomplishes the former objective. A
barb, guide vane or other in-stream structure directs scouring flows away from
the bank accomplishing the latter objective. When these two strategies are used
together, it is often possible to avoid hard armor altogether and to increase the
strength of the stream bank with vegetative or other less draconian means.
By balancing driving and resisting forces, the design team has a greater range of
choices for managing stream problems. This allows the team to achieve both
engineering and environmental objectives while reducing both capital and life
cycle costs.
5.1 Energy Management
The selective and advantageous use of hard points allows the designer to
balance energy, flow of water and flow of sediment by altering channel plan form
and profile. The most straightforward application of hard points is energy
management using hydraulic roughness. Modern river engineers do not
habitually minimize hydraulic roughness; they use it as a design tool. Rough
points created by structures or vegetation direct flow away from vulnerable areas.
Strategic use of hydraulic roughness also dissipates energy and lowers the
stress on bed and banks in general. This simple but useful insight is one reason
why old style hard armor has such a limited role in stream management.
Maintaining the capacity to transport bedload is equally important for maintaining
channel stability. This latter characteristic usually requires that high shear stress
be maintained in the center of the channel. Shear stress is a function of flow
depth and slope. A rock weir that is pointed upstream and angled down from the
bank to the center of the channel places the maximum depth and slope in the
center of the channel (Figure 5.1.0). Flow depth decreases gradually as the weir
approaches the bank. Because the weir is pointed upstream, the slope parallel to
the bank is lower because the crest width is longer relative to the bank rather
5-2
than perpendicular to the weir. The distribution of shear stress is non-uniform
across the rock weir. The unit shear stress (shear stress per unit width) is high in
the center of the channel and near zero at the stream bank.
High mid-channel stress
Top of Bank
Low near-bank stress
FLOW
THALWEG
Top of Bank
PLAN VIEW
Low nearbank stress
Scour pool
High midchannel stress
Low nearbank stress
Previous Grade
CROSS SECTION
Figure 5.1.0 Schematic of Rock Weir
The distribution of velocity across the channel is as important to aquatic life as to
physical stability. This type of structure, whether naturally occurring or manmade provides an important diversity of flows. The slack water areas behind the
rocks and near the bank are resting sites while the high velocity center flows
deliver well-oxygenated water and are prime feeding areas for predators. Similar
structures designed expressly for habitat improvement are widely used in the
Western U.S. (Rosgen, 2001).
Well designed in-stream structures are valuable design elements because they
efficiently fulfill three critical functions: 1) lowering near-bank stress, 2) providing
aquatic habitat and 3) maintaining transport capacity. Moreover, because these
structures are generally constructed from natural materials they are unobtrusive
and inexpensive. It is important to note that in-stream structures need not be
symmetrical. Often the departure angles of the structures are different on the left
and right sides when guiding flow through a meander or protecting bridge piers is
part of the design intent.
5-3
Changes in channel profile can be accomplished with grade structures
constructed of rock, logs or woody debris. Grade control structures are
especially useful for arresting incision. At-grade structures stop incision and slow
the generation of sediment at the existing channel elevation. A series of elevated
grade structures can reverse the incision and re-establish the pre-disturbance
bed elevation and slope. Elevated grade structures modify the effective bed
slope with commensurate influences on sediment transport and flow capacity.
These channels self-heal as sediment deposits and buttresses the toe of the
stream banks. This reduces the risk of bank failures. This approach is highly
effective. However, in flash-flood prone urban streams, flood capacity must be
maintained and elevated grade controls are not always appropriate.
While the primary purpose of grade structures is managing channel slope, the
location in plan form is critical, as is the spacing within a series of structures. In
stable streams, riffles occur at the point of inflection in the meander waveform.
Misplaced hard points can reset the riffles and, therefore, reset the stream’s
meander pattern. This meander resetting can induce widespread erosion.
Resetting the meander geometry watershed-wide can be unwittingly induced not
only by misplaced grade structures but by any structure that locally changes plan
form. This includes misshaped riprap slopes, poorly sited retaining walls and
progressively failing stormwater pipe outfalls.
5.2 The Role of Riparian Vegetation
Perhaps the most visible element of Natural Channel Design is the prevalence of
native riparian vegetation. In sharp contrast to conventional methods that strip
vegetation from streambanks, current management techniques take advantage
of the benefits afforded by woody vegetation.
Throughout much of the Midwest, riparian forests border undisturbed streams
through much of their length. The forest structure is relevant to stormwater
management because a dense, multi-layered stand increases rainfall
interception, storage and infiltration. As is characteristic of healthy forest stands,
the soils are rich with organic material and exhibit higher permeability than similar
soils on denuded lands. The quality of the forest structure has important
implications for stormwater management in the larger sense. Intact, high quality
forest is a stormwater management system in its own right (American Forests,
2000) and can offset the size and cost of conventional stormwater infrastructure.
Conversely, forest removal would only add to the burden on the rest of the
system. The effectiveness of the riparian forest is demonstrated by the
prevalence of springs feeding streams throughout our region on well-forested
stream banks two days after a rainfall. Functionally, the existing forest is an
infiltration/interception system. These systems provide stormwater benefits
through three distinct mechanisms. Interception, evapotranspiration and
infiltration into the soil account for the disposition of nearly all of the precipitation
5-4
reaching the forest (Ferguson, 1994, Federal Interagency Stream Restoration
Working Group, 1998). Forested soils are capable of infiltrating surprising
quantities of water and it is likely that many of our streamside forests are now
infiltrating runoff from nearby development in addition to the precipitation
reaching the surface directly. Water infiltrated through the forest soils migrates
through the vadose zone into the phreatic zone and eventually reaches the
streams through seeps. This subsurface discharge contributes to baseflow not
stormwater peak flows, a qualitative difference in terms of flood management,
erosion control and stream protection. Removal of the higher quality forest has
the net effect of increasing the quantity of stormwater that must be stored or
otherwise managed.
Many of the soils in the region are silty clay loams, generally considered poor
candidates for infiltration fields. Activities such as construction compaction,
tillage and even testing disrupt the aggregate structure of the soil and renders
silty clays nearly impermeable. However, well-structured silty clay loams rich in
aggregated particles and macropores have far higher permeabilities. Soil
aggregates are formed by interaction between clay particles and polysaccharides
generated by soil microorganisms. The interaction between clay particles and
humus via cation bridges (Bohn et al, 1985) and soil fungi such as the ectomycorrhizae that colonize oak roots forming large sub-surface networks of sticky
filaments further strengthen the aggregate structure. Macropores are channels
among the soil particles created and maintained by physiochemical processes,
plant roots and soil fauna. Other processes that form macropores are freezethaw cycles, weathering of bedrock and soil shrinkage due to desiccation of
clays. Forested areas have the most mature, well-established macropores. In
the upper horizon, macropores may occupy as much as 35% of the total volume
of soils. Macropores exert a disproportionate influence on infiltration rate as they
conduct water ahead of the wetting front in the general soil matrix. In clay soils,
even low percentages of macropores can increase hydraulic conductivity ten-fold
rendering clay soils nearly as conductive as gravels (Ferguson, 1994). It is
reasonable to propose that forests provide an important stormwater function and
should be preserved wherever possible. It would be useful to evaluate the
avoided storage provided by each of the forested areas as part of site
development plans.
5.3 The Role of Soil Bioengineering
The practice of using living plants to strengthen slopes is a seamless addition to
Natural Channel Design and often plays a critical role in re-establishing the many
functions of streams. When integrated into a plan of systemic stream
stabilization, soil bioengineering has proven to be a robust and cost-effective
treatment (Gray and Sotir, 1996).
5-5
In addition to improving water quality through shading and higher dissolved
oxygen, riparian vegetation stabilizes streams hydrologically, mechanically and
hydraulically.
The hydrologic effect derives from the ability of trees and shrubs to extract
immense quantities of water from the soil through evapotranspiration. The
resulting suction of soil moisture increases soil tensile strength. This process is
analogous to the post tensioning of concrete, which results in stronger concrete.
Recently, the National Sedimentation Laboratory reported that the
evapotranspiration effect on forested soils increases strength by 10-fold though
the increase sharply diminished during extremely wet years (Collison and Simon,
2001b).
The mechanical reinforcement derives from transfer of load from soil to root
fibers under shear stress conditions. The mechanisms of soil-root interaction
and the magnitude of root reinforcement have been investigated by Gray and
Leiser (1982) Gray and Ohashi (1983) Wu (1988) and Collison and Simon,
2001a). Through root reinforcement, soil shear strength is approximately doubled
in soils with good root penetration. Finally, riparian vegetation protects
streambanks more indirectly through hydraulic interactions. The hydraulic
roughness afforded by flexible vegetation shifts the high velocity flows away from
the streambank. By selectively shifting the distribution of high-energy, faster
flows toward the center of the channel, the shear stress on the streambank
reduces, thereby reducing erosion at the toe of the slope.
5.4 Alterations in Plan and Profile
The deliberate man-induced adjustment of plan form is sometimes called remeandering. Nature’s objective of meandering is to achieve equilibrium between
channel slope, width and wavelength. Franzius (1936) described the
methodology in the early 20th century. Once a stable waveform is determined
from geomorphic indicators, the remaining elements of stream geometry are
iteratively balanced to this form. In addition to achieving stable streams capable
of competently transporting the supplied water and sediment, stream plan form
geometry can be explicitly designed to reduce stress on bridge piers and other
infrastructure.
It is sometimes possible to alleviate localized flooding by altering bed slope and
channel form to convert the potential energy of the water to kinetic energy. The
channel conditions on either end of the treatment should, of course, be
appropriately designed for a smooth transition to the unaltered channel. This
more discrete approach often results in a much less intrusive channel treatment
with commensurately lower likelihood of a destructive stream response.
5-6
6.0 RESULTS
6.1 Fluvial Geomorphology of Fishpot Creek
Chapter Three presents the fundamentals of fluvial geomorphology. In that
chapter drivers and resistors of stream form are introduced. The drivers are the
quantity of water and the quantity of sediment while the resistors are the shape
and strength of the bed and banks. The SSMIP quantifies one of the two drivers
of stream form, but provides no insight on the resisting forces of stream form.
The hydraulic model documents how water moves through the system.
However, the main driver in Fishpot Creek is the quantity of sediment, not water.
As development progressed, the channel adjusted its shape to carry the water
delivered to it. In some areas the channel has been hardened by concrete, riprap
and gabions or is naturally strong with bedrock, cobble armoring, resistant clay
and vegetated loam. Flooding occurs in those reaches where the stream is
prevented from adjusting whether by a naturally resistant channel or man-placed
structures.
Throughout the watershed, channels continue to evolve in response to the
quantity of sediment. Like most urban streams, there are repeating zones of
erosion, transport and deposition separated by major bridges. Along the main
stem above the confluence with Holly Green Tributary, there are three such
zones, from the headwaters to Old Ballwin Road, Old Ballwin Road to Sulphur
Springs Road and Sulphur Springs Road to the confluence with Holly Green
Tributary. From the headwaters of Holly Green Tributary to the confluence of
Fishpot Creek and the Meramec River another zone of erosion, transport and
deposition occurs.
Stream response is also modified by geologic influences. Fishpot Creek’s
watershed is underlain by Mississippian limestone. The drainage pattern is well
integrated and moderately uniform. Upon examination of the remaining surface
streams, the basin appears to be of very low density. In an undisturbed
watershed, this would imply that the soil is deep with high infiltration. In this
highly disturbed watershed, the appearance of low drainage network density is
misleading; the intensive storm sewer piping renders this a highly dense
drainage network. The watershed evinces a moderate degree of angularity
overall with intermittent areas of high angularity. It is strongly oriented to the
northwest. When these drainage network features are evaluated together the
picture of the watershed’s character emerges. Fishpot Creek is dominated by
high energy flows with short times of concentration delivered to stream channels
with strong bedrock control and a proclivity to adjust along bedrock
discontinuities.
The bedrock bedding planes and joint sets are presented below as Table 6.1.0.
The orientation data is presented in the following format: strike direction/dip angle
and dip direction. Dip is the maximum inclination of a plane of structural
6-1
discontinuity to the horizontal. Dip direction is the direction measured clockwise
from North of a horizontal trace of the line of dip. Strike is the direction of the
intersection of an obliquely inclined plane with a horizontal reference plane and is
at right angles to the dip direction.
Bedding
Plane
N70°E/2N
N75°W/4N
Primary Joint
Sets
N5-10°E/80-90°E
N60°E/80-90°S
N45°W/70-90°S
N25°W/80-90°E
Secondary
Joint Sets
N40°E /NV*
N65°W/NV*
*NV: near vertical dip
Table 6.1.0 Bedding planes and joint orientation.
The results presented in Table 6.1.1 illustrate the correlation of drainage pattern
lineations to the primary and secondary joint sets measured in rock outcrops
throughout the watershed. The majority of meander migration is to the north or
east. This corresponds to migration down the dip direction of bedding and two of
the four primary joint sets.
Drainage
Pattern Lineal
Trends
N5°E
N40°E
N60°E
N65°W
N45°W
Primary Joint
Sets
Secondary
Joint Sets
N5-10°E/80-90°E
N40°E /NV*
N60°E/80-90°S
N65°W/NV*
N45°W/70-90°S
Table 6.1.1 Correlation of drainage orientation to bedrock joint sets.
As is apparent from the tables and discussion above, the bedrock has a profound
influence on the plan form orientation and significantly, on the direction of
meander migration. However, the underlying rock has less influence on the
overall profile of the stream. Locations of rock outcrops are presented on Figure
6.1.0. Figure 6.1.1 is the longitudinal profile of the main stem developed for the
hydraulic model and confirmed by a longitudinal profile we measured from Vance
Road to Manchester Road. There are no major knick points and flat runs
associated with the rock outcrops. In a bedrock-controlled profile, sharply defined
knick points and relatively flat runs are dominant features of the long profile. This
is not the case here. The bed shear developed in Fishpot Creek, in even frequent
6-2
storms, is capable of eroding and plucking the jointed and thinly bedded
limestone bedrock (Figure 6.1.2). The rock erodes in small steps along bedding.
While the bedrock has not posed a major impediment to the extent of incision, it
has played an important role in limiting the rate of incision. We noted local knick
points associated with the beginning of rock outcrops in most notably in Holly
Green Tributary and downstream of Manchester Road. Figure 6.1.3 presents
points along the stream that we identified as incising or stable in comparison to
rock outcrops. Incision is only occurring upstream of rock outcrops which are
locally influencing channel profile.
6-3
Figure 6.1.0 Rock Outcrops
38.61
38.60
Latitude
38.59
38.58
38.57
38.56
38.55
38.54
-90.59
-90.58
-90.57
-90.56
-90.55
-90.54
-90.53
-90.52
-90.51
-90.50
-90.49
Longitude
Rock outcrops
Waypoints
Figure 6.1.1 Longitudinal Profile
700
bed elev
650
Elevation feet
Q100 ws elev
600
Q2 elev
550
least squares bed
elevation
500
450
y = 8E-08x2 + 0.0014x + 395.15
400
350
0
10000
20000
30000
Stationing feet
6-4
40000
50000
Figure 6.1.2 Fishpot Creek
Shear Values, from Montgomery Watson SWMM data
Maximum shear, N/m2
10000
1000
100
10
1
0
5,000
10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 55,000
Stationing, ft above Meramac confluence
Q100 shear
Q15 shear
Q2 shear
Figure 6.1.3
Incising, Vertically Stable and Rock Outcrops Waypoints
38.61
38.60
Latitude
38.59
38.58
38.57
38.56
38.55
38.54
-90.59
-90.58
-90.57
-90.56
-90.55
-90.54
-90.53
-90.52
Longitude
Rock outcrop
Incising
6-5
Vertically Stable
Waypoint
-90.51
-90.50
-90.49
The next major feature influencing channel shape and strength is the soil. The
majority of the natural channel banks above Pepperdine Court are erosion
resistant clays. Cobbles and gravels armor much of the natural bed where
bedrock is not exposed. Chert layers and lenses are exposed in the banks
especially in Holly Green Tributary. These chert lenses are less resistant to
erosion than the clay soils and are a major contributor to the coarse sediment
bedload.
Overlying the bedrock is residuum derived from the weathering of the limestone.
The residuum is a gray to reddish gray clay containing layers and lenses of chert
fragments. The bed and bank of tributaries and headwaters often consist of
colluvium composed of gravel to cobbles in a clay matrix. Although loess and
loess-derived soils are common in this watershed, silt-dominated bank material is
rare in this watershed north of Big Bend. Alluvium lies below Big Bend and
Sulphur Springs Road.
In the St. Louis region, terrace surfaces of Pleistocene origin appear at an
elevation of about 500 feet. The surfaces tend to be relatively level over long
distances, and are likely the result of a higher base level in the Meramec River,
most likely through damming by debris and ice. These surfaces appear
prominently in Fishpot Creek’s watershed as broad flat valleys extending in
Fishpot Creek upstream of Sulphur Springs Bridge and in Holly Green Tributary
upstream of Big Bend.
This terrace has been largely reworked in lower Fishpot, but the surfaces above
the Holly Green Tributary - Fishpot confluence remain. Although silty
alluvium/lacustrine materials appear in banks along both reaches, incision, much
of it post-development, has exposed the more erosion-resistant limestone,
residuum, and chert-dominated materials.
In the reach along Vance Road near Pepperdine Court, however, silty material is
exposed in banks and was probably deposited during the Pleistocene period.
This much weaker material exposed by development-induced incision offers less
resistance to channel migration resulting in post-development channel migration,
a decrease in channel slope and massive deposition of coarse sediment.
Sediment
The analysis of the waterways in this watershed reveals an unmistakable linkage
between problems from the headwaters to the mouth. The headwaters
tributaries, particularly those feeding Holly Green Tributary, are incising and
generating massive quantities of sediment for delivery to the main stem. Holly
Green Tributary generated approximately 107,000 cubic yards of sediment since
development. Where the stream has sufficient power (Figure 6.1.4) to transport
this bed load, there are relatively few problems. However, at points of lower
stream power, the bed load is deposited in the streambed and in some cases
6-6
contributes to flooding either by constricting channels and culverts or by reducing
the velocity of the water enough to raise flow elevations. Throughout the
watershed, excessive sediment deposition is implicated in accelerated erosion
including widening and meander migration. The bed load delivered from the
headwaters is not well graded in the geotechnical sense. This means that the
particle sizes do not change uniformly from large to small.
Figure 6.1.4
Fishpot Main Stem
Q15 shear and specific power
700
2000.0
1800.0
600
Shear, N/m2
500
1400.0
1200.0
400
1000.0
300
800.0
600.0
200
Stream power, w/m2
1600.0
400.0
100
200.0
0
0
5,000
0.0
10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 55,000
Station in feet above Meramec confluence
Q15 shear
Q15 power
The absence of base flow from most of this stream eliminates the possibility of
classical pool-riffle analysis. Nevertheless, the forces that drive the alternating
patterns of scour and deposition are still operative. We measured particle size
distribution down the main stem and found a consistent gravel-cobble pattern
that is analogous to the pool-riffle sequence. The spacing between these
patterns is approximately six times the channel width; again analogous to the
pool-riffle sequence of flowing streams. The practical implications are important
for managing this stream. As stream power declines, so does Fishpot’s ability to
carry its bed load. The largest particles drop out first. Because the particle size
does not diminish in even, gradual intervals, the stream periodically has more
power than is necessary to carry the next smallest particle size and is still
sediment-hungry. In this case, the stream scours fine particles from the stream
banks until the sediment balance is reacquired. The bank scour is further
exacerbated by the tendency of coarse particles to deposit in central bars. The
bars separate the flow into two main threads and direct the flow against the
banks.
6-7
Downstream of the Hanna Road Bridge, Fishpot Creek begins to show a broadly
meandering form. Channel migration rates are generally low, point bars are
common, and banks are well vegetated with mature trees. There are few signs of
discontinuity in sediment transport. This reach also differs from upstream
reaches in that it is controlled by backwater from the Meramec River. At the
Meramec’s FEMA Q100 elevation of 432.0 feet, the Hanna Road Bridge deck is
nearly inundated, meaning that backwater effects would extend upstream some
distance even from Hanna Road, inundating roughly the lower 13,000 feet of
Fishpot. At the Meramec’s FEMA Q10 elevation, the inundation extends to Hanna
Road, which is 11,000 ft. above Fishpot’s mouth. During periods of flood flow in
both channels, sediment transport competence in Fishpot Creek would rapidly
decline at the point where backwater from the Meramec was encountered,
causing deposition of coarse sediment. During subsequent Fishpot Creek floods
uninfluenced by Meramec backwater, this sediment is remobilized. These
dynamics strongly influence local channel stability and flooding as is observed
along Vance Road at Pepperdine Court. At this location channel migration rates
are high. The silty bank material is easily eroded.
6.2 Dominant Fluvial Process
The locations of each reach and the geomorphic observations discussed below
are illustrated in Figures 6.2.0 through 6.2.8. These Figures are located at the
end of this section and referenced throughout the text.
Fishpot Main Stem
Clarkson Road to Fairview Drive Reach
See Figure 6.2.1. The uppermost reach of Fishpot Creek is adjusting in planform
through meander migration adjacent to Field Avenue. The adjustment in channel
geometry was precipitated by the addition of a new modular block wall on the left
descending bank at Field Avenue. Because of the wall’s low hydraulic
roughness, this reach has lower friction losses than adjacent reaches and,
consequently, higher stream energy is delivered downstream. The wall ends
immediately upstream of the typical high stress point in a bend with no transition
or protection against the increased stream energy. The wall is now being flanked
on the downstream end. On the opposite bank, riprap is being flanked on the
upstream end. This indicates that the meander is migrating downstream past the
armored channel. As the thalweg moves ahead of the channel centerline,
advancing the meander, it is eroding the bank at the upstream end of older
gabions and downstream end of new block wall. Channel widening was
observed 100 to 200 feet downstream of the migrating meander.
Immediately upstream of Fairview Drive, channel incision is the dominant
process. Channel incision may have been aggravated when the channel was
overwidened by the construction of the new Fairview Drive bridge. As a result, a
large volume of gravel and sediment liberated from upstream of the culvert was
transported downstream of the new bridge, initiating a new headcut upstream of
6-8
the Fairview Drive. Propagation of channel incision has been slowed by several
sanitary laterals crossing the channel. However, these crossings act as flat
weirs, collecting sediment and directing flow against both banks, resulting in
localized bank scouring.
Fishpot Main Stem
Fairview Drive to West Skyline Drive Reach
See Figure 6.2.1. This reach of Fishpot Creek is highly manipulated, with
gabions and dumped riprap covering the stream banks and Reno mattress lining
the channel bed. Extensive hard armoring of the banks and bed is not
continuous, but instead appears to be the cumulative result of spot fixes, each
one triggering an instability elsewhere along the reach. The alternating pattern of
hard-armor spot fixes and corresponding bank erosion illustrates the
ineffectiveness of treating systemic stream processes with traditional hard
armoring. This style of intervention does little to resolve systemic instability, but
instead shifts erosion or flooding elsewhere. Along this segment, the effects
were observed immediately upstream or downstream of hard-armor treatments.
Between Fairview Drive and West Skyline Drive channel widening is the
dominant fluvial process. In several locations the channel is adjusting through
meander migration. Channel widening and meander migration has been
amplified by Reno mattress hard armoring on the channel bed, which inhibits
vertical channel adjustment. In some locations, the stream has undermined
deteriorating gabions as it adjusts.
Fishpot Main Stem
West Skyline Drive to Manchester Road Reach
See Figure 6.2.2. Channel stability between West Skyline Road and Manchester
Road is predominantly influenced by coarse sediment deposition. Typical of
many of the reaches investigated in the Fishpot Watershed, culverts and channel
crossings influence the transport and deposition of these coarse bed materials.
Between West Skyline Drive and Smith Drive, much of the reach is stable in both
planform and profile, with localized meander migration approaching the Smith
Drive culvert.
Downstream of the Smith drive culvert the stream has been channelized with
gabions and Reno mattress. Overall, the channel maintains vertical and lateral
stability. Although two exposed sewer lines cross the channel near Applegate
Lane, the channel is not actively incising, but is depositional approaching
Manchester Road.
Fishpot Main Stem
Manchester Road to Ramsey Lane Reach
See Figure 6.2.2. The reach of Fishpot Creek between Manchester Road and
Old Ballwin Road is a stable transport reach. Downstream of Manchester Road,
the channel bed is exposed limestone bedrock, with a three to four foot bedrock
6-9
knick point. The prevalence of limestone bedrock in the channel bed and along
both banks has limited vertical and lateral channel adjustment.
Downstream of Old Ballwin Road there is substantial overbank dumping of wood
chips, plant buckets, pallets, mulch and other material along 500 to 600 feet of
the right descending bank behind the Ballwin Nursery. The overbank dumping
has created a local channel constriction that has accelerated meander migration,
compromising bank stability behind commercial property on both sides of the
channel. Downstream of the dumping an exposed sanitary sewer line acts as a
de facto grade control, approximately 200 feet upstream of the Ramsey Lane
culvert.
Fishpot Main Stem
Ramsey Lane to Reis Road Reach
See Figure 6.2.2. The double box culvert under Ramsey Lane has induced
flooding due to inadequate hydraulic conveyance, resulting from two obstacles at
the culvert. First, the right descending barrel under Ramsey Lane is blocked by a
vegetated sediment bar, hindering hydraulic conveyance through the culvert.
Second, the bottom of the culvert is too high, which also reduces hydraulic
conveyance. Downstream of Ramsey Lane, an exposed sewer line crossing and
grouted riprap armoring the pipe on both banks has constricted the channel.
This channel constriction is also responsible, in part, for localized flooding in the
vicinity of Ramsey Lane.
Downstream of the exposed sewer line, the channel is adjusting laterally through
meander migration behind homes along Ramsey Lane, directly north of Vail
Court. Complaints along Essen Lane and Rethmeier Court are in response to
bank erosion caused by continued channel migration. Approaching Reis Road,
meander migration diminishes, but the stream continues to adjust laterally by
means of channel widening. Coarse sediment deposition upstream of the Reis
Road culvert has triggered the channel widening and migration. The existing
quadruple box culvert under Reis Road is poorly aligned and perched above the
channel bed. These two factors influence sediment transport, as well as flood
frequency in the vicinity of the culvert.
Fishpot Main Stem
Reis Road to Sulphur Springs Road Reach
See Figure 6.2.3. Downstream of Reis Road the channel is stable in both
planform and profile, influenced by bedrock outcrops along the right descending
bank. Localized bank erosion and meander migration have been induced by a
short gabion-lined reach south of Brookside Lane. Meander migration has
resulted in advancing bank erosion along the right descending bank, behind
homes on Towercliff Drive and Treasure Cove. Bank scouring has also been
aggravated by several exposed sanitary sewer line crossings, which inhibit
hydraulic conveyance north of Treasure Cove.
6-10
Approaching Lindy Drive, the channel is concrete lined with a natural gravel
bottom. Most of the channel between Lindy Drive and Sulphur Springs Road is
concrete or riprap lined. The channel is vertically stable and primarily a sediment
transport reach, with channel widening and deposition downstream of the
concrete channel, near the newly constructed Sulphur Springs Road sewer line
crossing.
According to the SSMIP, flooding occurs between Lindy Drive and Sulphur
Springs Road and is localized in a 300 foot reach behind Chappel Court. The
Lindy Drive Bridge is a channel constriction and likely contributes to upstream
flooding. Downstream of the bridge the channel is concrete-lined, with point bars
extending from both banks. Approximately 600 feet to 700 feet downstream of
Lindy Drive, the bank height drops to about 4 feet from the base pool on the left
descending bank and 5 feet on the right descending bank. Near the end of the
concrete channel, an undercut sanitary sewer line is severely corroded, with
several small holes and metal patches from past repairs. Based on our field
reconnaissance, data analysis, and conversations with residents, flooding
through this reach is infrequent.
Fishpot Main Stem
Sulphur Springs Road to Wren Avenue Reach
See Figures 6.2.3 and 6.2.4. Downstream of the new Sulphur Springs Road
Bridge, the stream has established meanders through exposed limestone
bedrock, before making a transition to a gravel and cobble channel bed, with
banks influenced by channel widening.
Nearly half of this 3,000 foot reach, between Sulphur Springs Road and Wren
Avenue, is depositional. Mobile gravel in channel bars directs water and fine
sediment flow toward the banks during flood events. Upstream from the Wren
Avenue Bridge, the left descending bank is undercut. A scour hole has formed
immediately downstream of the steep bank. This steep bank and scour hole
represents the beginning of cut bank morphology accompanied by mobile
sediment bars that continues down to Wren Avenue. A recent wedge failure 500
feet upstream from Wren Avenue has generated a large volume of sediment.
Sediment has been deposited behind a tree that has toppled into the channel
from the right descending bank, acting as a turning vane. At Wren Avenue, two
of the three barrels at the bridge have been blocked with large woody debris,
liberated and transported downstream from failing banks upstream of the bridge.
Fishpot Main Stem
Wren Avenue to Big Bend Road Reach
See Figure 6.2.4. Of the three barrels under the Wren Avenue Bridge, only the
left barrel is unobstructed and open. On the downstream side of the bridge, the
left descending bank is actively eroding. A large scour hole has formed at the
end of the concrete culvert downstream of the left descending barrel of the
bridge, self-armored with large chunks of deposited limestone and grouted riprap.
6-11
Downstream of the scour pool, the channel is naturally armored with bedrock
outcrops. Approaching Big Bend Woods, channel bed slope flattens
considerably. Coarse bed material and introduced limestone riprap has been
deposited immediately upstream of the culvert inducing localized channel
widening.
Downstream of Big Bend Woods, scour along the left descending bank has
resulted from a misaligned triple box culvert under the road. However, the bank
erosion at this site has since been addressed as part of a sanitary sewer line
repair. From Big Bend Woods to the Bromfield Tributary confluence the stream
is stable. From the confluence with Bromfield Tributary, downstream to Big Bend
Road, the stream is depositional with chert gravel bed material and small
cobbles. Deposition upstream of the Big Bend Road culvert has induced bank
failures due to meander migration.
Fishpot Main Stem
Big Bend Road to Holly Green Tributary Reach
See Figures 6.2.4 and 6.2.5. After dropping through a wide, six to seven foot
deep scour pool located immediately downstream of the Big Bend Road culvert,
Fishpot Creek assumes an alternating bed sequence of coarse bed material and
fine bed material, typical of the Lower Fishpot sediment regime. This reach is
characterized by a wide, flat channel bed of gravel and small cobbles.
Downstream of Big Bend Road, the channel is, for the most part, stable until
reaching a series of high banks west of Westbrooke Terrace Drive and Stratford
Ridge Drive. The dominant process through this reach is meander migration
influenced by deposition.
The bank behind Westbrooke Terrace Drive is loess soil, overlain with
construction rubble and fill material. Perched groundwater is forced out at the
contact between these layers because the loess has been compacted at the
surface. The combination of groundwater seepage near the top of the bank and
an actively eroding bank toe has precipitated the advancing bank failure. A
second tall cutbank is behind Stratford Ridge Drive. Analysis of this reach
indicated that an existing sewer crossing upstream of the Stratford Ridge high
bank may be aggravating meander migration.
Fishpot Main Stem
Holly Green Tributary to Hanna Road Reach
See Figure 6.2.5. Downstream of the Holly Green Tributary, much of the reach is
bedrock-controlled, with a relatively flat channel bed of gravel and cobbles. The
channel is laterally stable and depositional until reaching a high-amplitude
meander near Vance Road and Pepperdine Court.
Near Pepperdine Court, moving average slope analysis indicates that the
effective channel slope drops to zero through this reach. The large bed load and
6-12
lack of stream power to effectively move the bed load is causing the stream to
meander as it drops the chert cobble and scours the loess and clay banks.
Meander migration along the right descending bank has resulted in advancing,
25 foot tall cutbanks threatening a section of Vance Road and five homes along
Pepperdine Court. The channel narrows behind Pepperdine Court, and a failed
attempt at bank stabilization has aggravated channel migration with collapsed
fabric-wrapped rock, which now acts as a turning vane, directing flow against the
right descending bank.
Meander migration continues downstream to Carriage Bridge Trails, before
widening between Wooden Bridge Trail and Glenn Brooke Woods Circle. Young
sycamores and woody vegetation have colonized the gravel bars through this
widened reach, indicating the earliest stages of recovery. Proceeding
downstream, the channel remains stable until reaching a channel constriction at
the Hanna Road bridge.
Fishpot Main Stem
Hanna Road to the Meramec River Confluence Reach
See Figures 6.2.5 and 6.2.6. A low-water crossing downstream of Hanna Road,
near Station 105+00, has interrupted water flow and sediment transport. This
induces coarse sediment deposition and localized bank erosion upstream.
Limestone riprap has been dumped haphazardly on two eroding banks upstream
of the low-water crossing. While riprap armoring has been a common response
to bank failures along this reach of Lower Fishpot, it is rarely effective at
preventing systemic bank failures and often amplifies damage by erosion.
From the Valley Park Tributary downstream to Vance Road the channel is
vertically stable with a tendency toward meander migration, influenced by
sediment supply, low bed slope, and Meramec River backwater. The reach is
relatively undeveloped and well vegetated. Several natural springs were
observed through rock outcroppings along the left descending bank towards the
downstream limits of this reach. The high cutbanks observed between the Valley
Park Tributary confluence and Vance Road do not appear to threaten existing
buildings or infrastructure.
Red Start Tributary
See Figure 6.2.2. Red Start Tributary flows to the northeast, through a 60 inch
concrete pipe under New Ballwin Road. Hard bank armoring is common
throughout the lower reaches of the stream. The banks along much of the
tributary are armored with gabions, formed concrete walls, or rubble and riprap.
The channel bed is fairly resistant to incision because it is limestone bedrock, as
are the toes of both banks. The tributary joins Fishpot Creek about 800 feet
downstream of Manchester Road.
6-13
Larkhill Tributary (SSMIP Branch D)
See Figure 6.2.3. The Larkhill Tributary is largely a piped stream, but has been
addressed in this report due to local flood concerns and the need for stormwater
management interventions.
Boleyn Tributary
See Figure 6.2.4. Boleyn Tributary maintains a fairly flat channel bed slope from
Boleyn Place down to Winding Path Lane. The undersized box culvert at
Winding Path is a de facto grade control and is responsible for maintaining the
channel grade upstream. Downstream of the Winding Path culvert, the channel
is incising and there is a six foot knick point in the bedrock channel bed. Channel
widening, coupled with the wholesale removal of riparian vegetation and canopy
cover, near the athletic fields at Parkway Southwest Middle School has resulted
in a very shallow channel shape (less than three feet deep), but otherwise stable.
Bromfield Tributary (SSMIP Branch C)
See Figure 6.2.4. The Bromfield Tributary daylights from a pipe east of Hanna
Road and flows west under Hanna Road bridge. This tributary has been highly
manipulated and the stream banks are heavily armored with gabions, formed
concrete walls, or modular block walls. Because the Bromfield Tributary is
currently incising, the flows of the tributary are undermining these structures in
the upper reaches of the tributary.
Downstream of Hanna Road the channel is vertically stable. However, gradual
channel widening and meander migration continues behind residential property
on Wayfarer Drive. The stream is vertically and laterally stable from Wayfarer
Court to the confluence with Fishpot Creek main stem.
Holly Green Tributary (SSMIP Branch B and B1)
See Figure 6.2.8. Originating from a culvert and detention basin north of Cleta
Court, Holly Green Tributary is an actively incising stream. The exception to this
classification is a segment downstream of Cleta Court to the culvert at Brightfield
Drive. There, the channel has widened and, presently, sediment is depositing in
with pioneer species of vegetation colonizing the banks.
Downstream of the culvert at Brightfield Drive, the stream again shows evidence
of channel incision. There are several limestone bedrock knick points
downstream of Brightfield Drive, with the tallest knick point standing nearly three
feet high. Although much of the channel is limestone bedrock, flow in the
tributary continues to pluck rock and deepen the channel.
New Ballwin Tributary
See Figure 6.2.8. New Ballwin Tributary daylights from a pipe at New Ballwin
Road and runs to the southeast, passing under two bridges, before joining the
Holly Green Tributary, east of Reis Road. The channel shows signs of past and
present channel incision. While channel incision appears to have ceased
6-14
downstream of the Rustic Valley Drive Bridge, upstream of the bridge channel
incision is ongoing, generating large volumes of coarse bed material.
Downstream of Mark Wesley Lane, the stream is gradually recovering from past
channel incision and is now depositional in nature. Deposition-induced channel
widening poses a threat to channel stability and adjacent infrastructure upstream
of Mark Wesley Lane and meander migration poses a similar threat near Reis
Road.
Old Ballwin Tributary
See Figure 6.2.8. Old Ballwin Tributary flows to the southeast from a culvert
outfall under Old Ballwin Road passing under Talbert Court, Madrina Court,
Twigwood, and Mark Wesley Lane before reaching Reis Road. The channel has
been locally widened at the culvert under Talbert Court and Madrina Court. The
smooth concrete channel and a resulting increase in hydraulic slope accelerates
water under Talbert Court propagating channel incision upstream. Evidence of
past channel incision was also observed between Madrina Court and Reis Road,
but the channel appears to have since stabilized laterally and vertically. Old
Ballwin Tributary joins Holly Green Tributary upstream of Big Bend Road.
Ferris Park Tributary
See Figure 6.2.8. The Ferris Park Tributary daylights from a pipe outlet at New
Ballwin Drive and flows east to its confluence with New Ballwin Road
approximately 500 feet west of Reis Road. In the upper reaches of the Ferris
Park Tributary the channel is U-shaped, with high scour lines and surfing bank
vegetation, indicating active channel incision. In many of the Fishpot tributaries a
bedrock-controlled channel bed has slowed, but not stopped the progress of
incision.
Haphazard dumping of limestone riprap was done in attempts to spot-fix and
armor failing banks. Because these banks continue to fail in response to ongoing
channel incision, these attempts to curtail bank erosion proved unsuccessful.
The periodic stream flow has washed away much of the dumped riprap and
transported it downstream.
Towerwood Tributary
See Figure 6.2.8. Towerwood Tributary is a small tributary, originating at
Towerwood Drive and feeding into the New Ballwin Tributary downstream of
Great Hill Drive. Immediately downstream of Great Hill Drive Towerwood
Tributary used to be a detention pond. When breached channel incision
propagated upstream. Upstream of Great Hill Drive, incision has resulted in
stream bank erosion threatening residential property along both banks.
Valley Park Tributary (SSMIP Branch A)
See Figure 6.2.6. The first of ten contributing tributaries in the Fishpot
Watershed, the Valley Park Tributary exemplifies the dominant channel-forming
processes and morphological stage of the majority of tributaries in the watershed.
6-15
Channel incision continues to liberate bed and bank material in the upper portion
of the tributary. This material is then deposited downstream near the confluence
with Fishpot Creek main stem, initiating meander migration.
Two bridges cross the stream: the first is Autumn Leaf Drive Bridge, near Station
40+00, and the second is the Crescent Road Bridge, near Station 30+00.
Presently, the stream has incised up to the Crescent Road Bridge. A knick point,
nearly six feet high in exposed limestone bedrock, occurs downstream of
Crescent Road. This knick point indicates the severity of the channel incision up
to this point. However, the upstream progression of incision has been temporarily
controlled by the relatively resistant bedrock.
The channel is depositional through the lower 300 feet of the tributary, upstream
of the confluence with Fishpot Creek main stem. All geomorphic indicators
suggest that the channel has completed a stage of past channel incision and is
now adjusting in planform by meander migration.
6-16
7.0 RATIONALE FOR TREATMENT PRIORITIES
The treatment priorities are based on the principles of geomorphology described
in this report and on risk of flooding described in Walesh (1989). The common
practice in the metropolitan area is still based on landowner complaints and the
results of the hydraulic model. This prejudices designers towards site-specific
repairs without considering the cause of the problem. This does not imply
insensitivity towards landowner complaints. They certainly must be addressed;
however complaints are best addressed in a systemic manner so that treatment
of one complaint does not generate the next one. The following priority scheme
focuses on addressing the fundamental cause of instability. The lower priority
sites represent problems of lesser influence on systemic stability or localized
problems.
• Priority 1: Hazard – These projects address conditions posing a nearterm threat to public safety or significant infrastructure and should be
repaired promptly. All exposed sanitary lines receive this priority
because of their potential influence on public health and water quality.
In addition, sites exhibiting clear evidence that a long delay in
treatment will potentially lead to a permanent loss of property or a
dramatic increase in the cost of treatment directly associated with the
progression of the problem receive a priority 1. Habitable structures
and roadway flooding from the 15-year or less recurrence storm
receive a priority 1. The risk of flooding over a 30-year period, the
length of an average mortgage, is 87.4 percent.
• Priority 2: Systemic – These sites, while not posing an immediate
public hazard, are fundamentally unstable with clear influence
elsewhere in the watershed. These are often streams in Stage III or IV
(active incision or widening). If left untreated, the channel adjustment
will continue and will generate more problems. Priority 2 projects are
not emergencies but should be addressed as soon as funding permits.
Because the generation of coarse sediment are so strongly implicated
in both flooding and erosion problems watershed wide, tributaries
generating significant sediment receive this rating irrespective of
whether there is an associated complaint.
• Priority 3: Supporting – Like priority 2 projects, these are a
consequence of the channel adjustment induced by previous channel
manipulation. However, either because of location in the watershed or
particularly robust features adjacent to the site, propagation of the
problem is less likely or is proceeding relatively slowly.
• Priority 4: Localized – These problems are distinct from the two
previous categories in that the cause is local rather than systemic.
Examples of this type of problem include overbank drainage, removal
of riparian corridor, and debris or yard waste dumping.
• Priority 5: Enhancements – These are opportunities to prevent future
problems, reduce water and sediment conveyance stress on the
7-1
stream system or to otherwise improve stream performance. This
category includes projects that increase infiltration, dissipate or direct
energy, or re-establish a normal grade for stream banks.
7-2
8.0 PROPOSED INTERVENTIONS
In the following section we present a series of recommendations for sustainable
management of Fishpot Creek. We have addressed each SSMIP
recommendation with an intervention or management strategy that not only
addresses the local flooding or erosion concern, but maintains systemic stream
stability and sediment transport competency in the watershed. The explicit
purpose of our recommendations is to prevent relocation or aggravation of
stability problems elsewhere in the watershed. It is imperative that each
management recommendation is founded on a thorough analysis and
understanding of the systemic processes and not exclusively in reaction to
complaints, problem visibility, or proximity.
In the following paragraphs, interventions are described as 319 REACH NAME
RECOMMENDATION NUMBER. For example, 319MS01 is the first (and most
upstream) recommendation of the Main Stem while 319VP4 is the fourth (and
most downstream) recommendation for the Valley Park tributary. The locations of
each intervention are illustrated in Figures 8.0 through 8.8. These Figures are
located at the end of this section and referenced throughout the text.
Fishpot Main Stem
•
319MS01 – Guide Vanes at Field Avenue. See Figure 8.1. The purpose
of the guide vanes is to reduce the erosion caused by a new modular
block wall on the left descending bank at Field Avenue. By increasing
near-bank stream energy, the wall has induced erosion at its downstream
end. The increased stream energy is caused by the low hydraulic
roughness of the wall coupled with a near vertical slope. The wall ends
immediately upstream of the highest stress point in the bend with no
transition or protection against the increased stream energy. This has
induced scour and erosion of the left descending bank immediately
downstream of the new wall. Riprap in the stream bed and along right
descending bank, across from the wall, is being flanked on the upstream
end.
Meander migration is the dominant fluvial process through this reach. The
meander is advancing downstream past the armored channel. As the
discharge flowline moves ahead of the channel centerline, advancing the
meander, it is eroding the bank at the upstream end of rip rap and
downstream end of block wall. We recommend installing guide vanes to
protect the upstream edge of riprap and downstream edge of wall by
guiding the meander turn. Guide vanes focus flow and direct the highest
shear stresses to the center of the channel and away from vulnerable
banks. The effect of properly designed guide vanes is almost precisely
8-1
the opposite of smooth, hard bank armor. Bank armor concentrates stress
at the toe of the stream bank while guide vanes lower near-bank stresses.
This treatment will also prevent flanking of the riprap and failure of the wall
due to erosion flanking the new wall from the downstream edge.
•
319MS02 - Grade Stabilization and Sewer Lateral Protection. See Figure
8.1. Upstream of Fairview Drive, channel incision is the dominant process.
Propagation of channel incision has been slowed by several sewer laterals
crossing the channel. However, these crossings act as flat weirs,
collecting sediment and directing flow against both banks, resulting in
localized channel widening. Upon the installation of the new Fairview
Drive Bridge, the channel was overwidened. This induced a head cut
advancing upstream from the new bridge liberating a large volume of
gravel and sediment from upstream of the culvert. We recommend a
series of grade controls incorporating a stable low flow width upstream of
Fairview Drive to protect the sewer laterals, control channel incision,
relieve stress on banks, and control sediment flow.
Fishpot Main Stem
•
319MS03 – Bankfull Floodplain Downstream of Fairview Drive Bridge.
See Figure 8.1. The dominant process downstream of the Fairview Drive
Bridge is channel widening with subsequent meander migration. Field
observations indicate the new bridge and inadequate sediment transport
through the reach are aggravating meander migration. This reach is also
prone to flooding. It is not clear whether the new Fairfield Drive Bridge
alleviated flooding. A pedestrian bridge and undermined sewer line
crossings at the upstream edge of Cardinal Park (at the downstream end
of this reach) are constricting the flow, which may continue to aggravate
flooding.
To restore sediment transport competency, alleviate channel migration in
this reach and reduce flooding potential, we recommend a two stage
channel with a bankfull floodplain along the left descending bank
downstream of the culvert, and guide vanes along the toe of the right
descending bank to reduce near bank stress. The overbank or floodplain
should extend downstream of the pedestrian bridge and in-stream utilities
to provide conveyance around these channel constrictions.
•
319MS04– Re-shape De facto Turning Vane. See Figure 8.1. An existing
concrete weir in Mockingbird Park, north of Ranchmoor Trail, is turning
flow towards the right descending bank causing scour, resulting in a tall,
steep cut bank. While the reach is vertically stable or depositional, the
dominant process is channel widening with subsequent meander
migration. We recommend reshaping and reinforcing the existing
8-2
concrete structure with rock and shaping it into a V-shaped weir to direct
flow away from bank. Adding rock and shaping the existing weir is much
less expensive than removing the existing concrete.
•
319MS05– Flood Proof Homes. See Figure 8.1. Two structures
susceptible to flooding are located on the top of the left descending bank.
Both homes are flooded by the 100-year storm. We concur with the
existing recommendation of floodproofing the structures.
•
319MS06 – Relocate Utility Lines on Eroding Bank. See Figure 8.1. Utility
poles downstream of a gabion-lined reach, south of Providence Road and
Monteith Drive, are threatened by bank erosion. The gabions effectively
channelized the reach immediately upstream of this location and, as a
result, increased stream energy. There is no transition where the gabions
end and the unarmored stream banks resume. In response to the
increase in energy, the channel is widening and adjusting meander
pattern. We recommend moving the utility poles out of harm’s way.
•
319MS07 – Armored Scour Pool, Bank, and Bed Protection. See Figure
8.1. A scour pool has developed at the end of the Reno mattress-lined
channel behind Westridge Elementary School. Localized scour has been
triggered by the Reno mattress-lined channel and corresponding increase
in stream energy. We recommend replacing the existing scour pool with a
designed scour pool armored with vegetated rock. We also recommend
placing a weir at the downstream limits of the scour pool to hold grade and
focus the flow at the point of release. The surrounding banks should be
stabilized as appropriate and revegetated with native riparian species.
Urban forestry will also be necessary as part of this intervention to remove
invasive, non-native species and to preserve riparian vegetation with bank
stabilizing qualities.
Fishpot Main Stem
•
319MS08 – Bankfull Floodplain and West Skyline Bridge. See Figure 8.1.
Between West Skyline Drive and Smith Drive, much of the reach is
vertically and laterally stable. We note limited, local meander migration
approaching the Smith Drive culvert. Based on the geomorphic analysis,
the average stream width at the base of the channel upstream of the West
Skyline Culvert is 28 feet. We estimate bankfull width to be approximately
30 feet, as determined by a persistent lower limit of woody vegetation
along the left descending bank at 2.5 feet above the channel bed. The
existing channel slope is roughly 0.008 upstream of the existing West
Skyline culvert. The hydraulic analysis indicates structure flooding
upstream of West Skyline Drive and overtopping of West Skyline Drive.
8-3
Based on these parameters, we recommend replacing the existing West
Skyline culvert with an 80-foot span bridge and constructing a stable, twostage channel under the bridge and through the reach. Concept level
calculations indicate that fluvial process and flood flows can be
accommodated by excavating a 15-foot wide bankfull floodplain, or flood
bench, at the bankfull height (2.5 feet above the channel bed), with 3:1
vegetated side slopes and vegetated rock at high stress areas. The low
flow channel will accommodate sediment transport and fluvial process
during dominant discharge, while the bankfull floodplain will provide
capacity during high flows without causing damage upstream or
downstream of the project site.
These two interventions, construction of the two-stage channel and
replacement of the culvert, are not separable. The constriction at the
West Skyline culvert must be removed. However, providing bankfull
capacity without preparing the channel upstream will induce high flow
erosion and may not address the flooding. Conversely, providing the
bankfull upstream without changing the West Skyline constriction may not
adequately resolve flooding problems.
•
319MS09 –Smith Drive Bridge. See Figure 8.2. Immediately upstream of
the Smith Drive culvert, the dominant process is channel widening with
subsequent meander migration. Downstream of the Smith Drive culvert,
the channel is stable. There is a 1.5 foot knick point immediately
downstream of the Smith Drive culvert. The hydraulic analysis indicates
that Smith Drive is overtopped during the 100-year storm and there are
complaints of infrequent flooding both upstream and downstream of Smith
Drive.
To alleviate property flooding and overtopping of the Smith Drive culvert,
we recommend removing the existing triple box culvert and replacing it
with an 80-foot span bridge. We also recommend incorporating the 1.5
foot knick point into the design to improve conveyance under the new
bridge. This can be accomplished by installing grade controls upstream
and downstream of the bridge effectively turning the knick point into a
steep knick zone between the grade controls. We recommend a twostage channel design that accommodates the increase in slope between
the two grade controls. Transition zones are necessary upstream and
downstream of the interventions to insure the local slope increase does
not cause damage elsewhere in the watershed.
8-4
Fishpot Main Stem
•
319MS10 - Manchester Road Bridge. See Figure 8.2. Upstream of
Manchester Road, Fishpot Creek is vertically depositional and laterally
stable at the lower end of the reach while the upstream end is migrating
and widening. Downstream of Manchester Road is a stable transport
reach with bedrock control. There are complaints of frequent structure
flooding immediately upstream and downstream of Manchester Road and
frequent overtopping of Manchester Road. The hydraulic model indicates
significant backwater upstream of the existing Manchester Road culvert.
The existing double box culvert under Manchester Road is unable to
accommodate flow and sediment transport. Field observations indicate
that flooding upstream of Manchester Road is aggravated by deposition
immediately upstream of the culvert.
We recommend replacing the existing culvert with a 100-foot span bridge
to accommodate both sediment transport and large storm flows. Sediment
transport and channel stability will be accommodated with a two stage
channel under the bridge. The new bridge and channel design should
include a hydraulic model of proposed conditions to determine the effect of
the new bridge on flooding upstream and downstream. The existing
recommendation of floodproofing property upstream and downstream of
the new bridge should be included in this project if it is still necessary.
•
319MS11 – Reinforce Existing Knick Point. See Figure 8.2. There is a
knick point in bedrock downstream of Manchester Road. This is a stable
transport reach. Bedrock is being plucked out at the knick point over time
through freeze thaw cycles. The knick point is therefore migrating
upstream at a very slow rate. We recommend reinforcing the knick point
with a large grade control to prevent the slow propagation of channel
incision upstream.
•
319MS12 – Floodproof Structures at Old Ballwin Road. See Figure 8.2.
There are complaints of structure flooding upstream and downstream of
Old Ballwin Road. There are also complaints of channel erosion
downstream of Old Ballwin Road. This is a stable reach. The bank erosion
is caused by overbank dumping of wood chips, plant buckets, pallets,
mulch and other material along 500 to 600 feet of the right descending
bank immediately downstream of Old Ballwin Road.
We recommend floodproofing the three structures immediately upstream
and downstream of Old Ballwin Road. The bank erosion is a self-inflicted
problem caused by excessive overbank dumping and therefore not a
public improvement problem. We recommend the local business acquire a
8-5
404 or 401 permit and remove all the material that they’ve dumped back to
the original bank line and stabilize it with vegetative methods.
•
319MS13 – Protect Sanitary Line. See Figure 8.2. A grouted sanitary
sewer line about 200 feet upstream of Ramey Lane is acting as a grade
control. This is a stable reach. We recommend constructing a grade
control immediately downstream of the sewer crossing to prevent future
undermining and to reduce stress on the sanitary line.
Fishpot Main Stem
•
319MS14 – Add Bankfull Flow Capacity at Ramsey Lane. See Figure 8.2.
Ramsey Lane is being overtopped in the 15-year storm and there is a
flooding complaint of one business along the left descending bank
immediately upstream of Ramsey Lane. A sanitary sewer crossing is
restricting flow immediately downstream of Ramsey Lane. The reaches
downstream and upstream are stable. Any recommendation to alleviate
flooding must also accommodate natural stream function. To reduce
flooding and overtopping of Ramsey Lane we recommend adding capacity
to the high flow channel. No flood elevation modeling was performed as
part of this analysis. The SSMIP model concluded two parallel 8 foot by 12
foot barrels would eliminate flooding. We assumed four smaller barrels
would be necessary. The new barrels must be constructed at the bankfull
elevation which is about 3 feet higher than the existing culvert sill. By
adding capacity to the overbank only, we do not over widen the stream,
which would result in immediate stream instability and damage upstream
and downstream. The barrels should be split with three new barrels on the
right descending side and one new barrel on the left descending side.
We also recommend removing the channel constriction at the sewer line
crossing downstream of Ramsey Lane. After removing the grouted riprap
on either side of the channel the banks should be stabilized by installing a
composite revetment.
•
319MS15 – Weirs Upstream of Reis Road. See Figure 8.2. There are
complaints of bank erosion upstream of Reis Road along Essen Lane and
Rethmeier Court. This reach is laterally widening or migrating and
vertically stable with occasional depositional features. Coarse sediment
deposition upstream of the culvert has triggered the channel widening and
migration upstream of Reis Road.
We recommend installing a series of upstream pointing weirs through the
widening and migrating reach. The weirs will allow sediment transport,
while reducing near-bank shear stress along the bank toes. The last rock
weir in the series (closest to Reis Road) should also be designed as a
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grade control. The rock structures should be constructed low enough that
they are hydraulically transparent during high flows thereby causing no
adverse effect on flood conveyance.
We recommend constructing this intervention in conjunction with
319MS16 – Reis Road Bridge.
•
319MS16 – Reis Road Bridge. See Figure 8.2. The hydraulic model
indicates that the Reis Road culvert is overtopped by the 100 year flood.
The existing culvert is poorly aligned and perched above the channel bed.
These two factors not only influence flood frequency, but also influence
sediment transport and the deposition responsible for upstream bank
erosion. We recommend removing the existing four 8 foot by 12 foot
barrel culverts and replacing them with a 100-foot span bridge. The new
bridge will include a two stage channel to accommodate fluvial process
and sediment transport through all flows. Since the existing culvert is
perched, the new channel under the bridge will be lower than the existing
culvert sill, which will help maintain sediment transport competence.
Fishpot Main Stem
Reis Road to Lindy Drive Reach
•
319MS17 – Bankfull Floodplain between Reis Road and Lindy Drive. See
Figure 8.3. There are several complaints of structure flooding along this
reach. The upper portion of this reach along Brookside Lane is bedrock
controlled. It is stable in profile and generally stable in plan and crosssection although there is some local lateral migration. The lower portion of
this reach is concrete lined with a natural gravel bottom. We recommend
using a combination of a bankfull floodplain and locally raising the low
points along the bank. This will mitigate property flooding along this reach
without damaging the upstream and downstream reach. Concept level
analysis indicates that a 36 foot wide bottom with a 20 foot wide bankfull
elevated 3 feet above the channel bed will accommodate both dominant
discharge and flooding flows. The concept level analysis included 2H:1V
side slopes for the low flow channel and 3H:1V side slopes for the high
flow channel.
•
319MS18 – Lower Exposed Sewer Lines between Reis Road and Lindy
Drive. See Figure 8.3. There are several existing sanitary sewer lines
exposed in the bed or crossing aerially up to two feet above the flowline of
main stem Fishpot. We recommend lowering these lines to remove the
obstruction and protect the sewer utility. Removal of the existing sanitary
sewer line will also help reduce localized flooding.
8-7
Fishpot Main Stem
Lindy Drive to Wren Avenue Reach
•
319MS19 – Bankfull Floodplain Between Lindy Drive and Sulphur Springs
Road. See Figure 8.3. There are several complaints of structure flooding
along this reach from Lindy Drive to Chappel Court and Woodland Hill
Court. The reach is a concrete prismatic channel. There is a four foot drop
in bed elevation near the end of Jamboree Drive and an elevated ten inch
ductile iron pipe sewer line with concrete wing walls forming a constriction
at the bottom of the reach. Immediately downstream of Lindy Drive, there
is a depositional feature including center bars. Downstream of the
depositional area, this is a stable transport reach.
To maintain adequate sediment transport at lower flows and reduce
flooding during high flows, we recommend removing the concrete channel
and installing a two stage channel. This project should be done in
combination with 319MS20– Replacement of Aerial Sewer Line at
Chappel Court. The existing four foot drop in bed elevation can be
incorporated into the final design to locally steepen the water surface if
needed for locally lowering the water surface elevation during extreme
storms. Concept level analysis indicates that a 40-foot wide bottom with a
20-foot wide bankfull floodplain elevated three feet above the channel bed
will accommodate dominant discharge and flooding flows. The concept
level analysis included 2H:1V side slopes for the low flow channel and
3H:1V side slopes for the high flow channel.
The combination of 319MS16 and 319MS18 presents a rare opportunity to
take Fishpot Creek out of its existing concrete lined condition and restore
it to a more natural channel form. Not only will this address the flooding of
many homes along the creek, but it will restore some of the natural
functions of the stream. Once vegetated, the new channel will be much
more beautiful and accessible to residents. As the native riparian plants
mature, the stream will take on a park-like appearance which could
increase property value. Homeowners will benefit from improved
aesthetics and increased property value and Fishpot Creek will benefit
from improved water quality, riparian corridor and aquatic habitat.
•
319MS20 – Replacement of Aerial Sewer Line at Chappel Court. See
Figure 8.3. Concrete and cobbles have accumulated along the exposed
sanitary sewer line crossing. The accumulated material is inducing a local
increase in water elevation during high flow events. We recommend
lowering this sanitary sewer line to alleviate local flooding.
•
319MS21 – Analysis of Sulphur Springs Approach and Knick Zone. See
Figure 8.3. Sulpher Springs Road was re-aligned and a new bridge over
Fishpot Creek was installed as field analysis for this project progressed.
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An existing three-foot knick point at the old Sulphur Springs Road crossing
was identified at the beginning of this analysis. The knick point may not
have been adequately addressed by the construction of a trapezoidal
rock-lined approach to the new Sulphur Springs Road Bridge. If the
transition is inadequate, there is a possibility that the new construction will
generate damage to the natural channel upstream and downstream. We
recommend analyzing the new site to evaluate the potential of an
advancing headcut and then design solutions as appropriate. We
assumed four stream structures as a base for estimating construction
cost.
•
319MS22 – Turning Vanes Upstream of the Wren Avenue Culvert. See
Figure 8.4. The Wren Avenue culvert is a triple box with 12-foot wide by
18-foot tall barrels. On three occasions during our field analysis we
observed substantial debris and log jams on the front edge of the culvert.
The reach upstream of the Wren Avenue Culvert is depositional and
adjusting in plan form. Field observations indicate the debris jams on the
Wren Avenue Culvert are aggravating sediment deposition upstream. The
deposition, in turn, accelerates meander migration and erosion. Erosion
on the left descending bank has exposed a sanitary sewer line.
We recommend a series of stream barbs or weirs to define a low flow
channel for efficient sediment transport. The weirs should be designed to
reduce near-bank shear forces. The combination of improved sediment
transport and reduction in bank shear will substantially reduce the lateral
migration and protect threatened infrastructure. We also recommend
removing the existing log jam and installing a debris trap at a convenient
location upstream of the culvert. This will reduce debris build up at the
culvert and provide a convenient location to access and clean debris out
of the channel.
Fishpot Main Stem
•
319MS23 – Turning Vanes Downstream of the Wren Avenue Culvert. See
Figure 8.4. Bank scouring continues along the left descending bank
downstream of the Wren Avenue culvert. To prevent further scour, we
recommend installing turning vanes along the left descending bank
immediately downstream of the Wren Avenue culvert.
•
319MS24 – Meander Migration Monitoring, Upstream of Big Bend Road.
See Figure 8.4. The stream is generally stable between Big Bend Woods
and Big Bend Road. However, approximately 200 feet upstream of Big
Bend Road local meander migration has accelerated bank erosion along
the left descending bank. The rate of migration is unclear. We recommend
installing erosion pins along the left descending bank and monitoring the
8-9
rate of migration. If significant movement is detected, an appropriate
response can then be designed.
Fishpot Main Stem
Big Bend Road to Holly Green Tributary Reach
•
319MS25 – Protect Stratford Ridge High Bank. See Figure 8.5. High
banks are common downstream of Big Bend Road and Westbrook
Subdivision between Stratford Ridge Drive and the confluence with Holly
Green Tributary. The first of these high banks appears behind Stratford
Ridge Drive. The process is deposition inducing meander migration. Field
analysis indicates that an existing sewer crossing upstream of the
Stratford Ridge high bank may be aggravating the migration.
We recommend installing a series of weirs and guide vanes to control
migration and reduce bank shear on the high Stratford Ridge high bank.
The structures could start at the existing diagonal sewer line crossing
upstream. The existing sewer crossing could be turned into the upstream
most-weir by adding another leg of riprap or grout mirroring the existing
crossing about the center of the channel. Installing guide vanes along the
high bank and weirs to focus stream forces through this reach would help
reduce further bank erosion.
The high bank is about twenty feet tall with a field behind it mowed to the
top of bank. We recommend regrading the bank to a traversable slope and
re-vegetating with riparian plants. This reduces the hazardous steep slope
and restores some of the lost riparian corridor at this location. The bank
regrading with a riparian corridor adds about $150,000 to the construction
cost. If this cost is prohibitive, we recommend a fence at the top of slope
to reduce the steep bank hazard. Of course, if the fence option is selected,
the stormwater and habitat benefits will not be achieved.
•
319MS26 – Protect High Bank Downstream of Stratford Ridge. See
Figure 8.5. Nearly 1000 feet downstream of the Stratford Ridge high
bank, a second high bank on the left descending side requires similar
treatment. Again, we recommend installing a series of weirs and guide
vanes to reduce bank shear on the high bank.
Fishpot Main Stem
Holly Green Tributary to Hanna Road Reach
•
319MS27 – Guide Vanes at Main Stem and Holly Green Confluence. See
Figure 8.5. The main stem is laterally migrating at the Holly Green
Tributary confluence. The migration could potentially threaten the new
Fishpot East Sanitary Main. There is no immediate threat. We recommend
a series of guide vanes to relieve near bank shear and reduce the threat
8-10
of future migration and erosion. This may also involve re-sloping and revegetating portions of the right descending bank.
•
319MS28 – Pepperdine Reach Bank Stabilization. See Figure 8.5. Bank
erosion is threatening a section of Vance Road and five homes along
Pepperdine Court. Extensive deposition has prompted plan form
adjustment of the channel. From analysis of the moving average slope it is
apparent that the effective channel slope drops to zero through this reach.
The large bed load and lack of stream power to move the bed load drives
the stream to meander as it drops the chert cobble and subsequently
scours the loess and clay banks. Meander migration along the right
descending bank has resulted in advancing, high cut banks near Vance
Road and behind Pepperdine Court. The channel narrows behind
Pepperdine Court. Here a failed attempt at bank stabilization exacerbates
the migration as a collapsed fabric-wrapped rock acts as a turning vane,
directing flow against the already eroding right descending bank. The top
of bank along Pepperdine Court has retreated over 15 feet in the last three
years.
We recommend using a combination of weirs and guide vanes to define a
low flow channel capable of transporting sediment through this reach. The
guide vanes will also reduce the near bank shear thereby reducing the
erosive forces on the high banks.
Fishpot Main Stem
Hanna Road to Meramec River Confluence Reach
•
319MS29 – Hanna Road Bridge Improvement. See Figure 8.5. Hanna
Road is frequently overtopped during moderate storms. The capacity of
the existing bridge is inadequate for either water or sediment conveyance.
Consequently, the reach immediately upstream of Hanna Road includes
substantial deposited sediment. The poor sediment transport capacity
here induces local sediment dams which locally aggravating flooding.
We recommend raising Hanna Road and building a new bridge with a two
stage channel underneath to accommodate sediment transport as well as
extreme storm flows. Concept level analysis indicates that a 45-foot wide
bottom with a 100-foot wide bankfull floodplain elevated four feet above
the channel bed will accommodate dominant discharge and flooding flows.
The concept level analysis included 2H:1V side slopes for the low flow
channel and 3H:1V side slopes for the high flow channel. The new Hanna
Road Bridge should span a minimum of 200 feet.
•
319MS30 – Remove the Low Water Crossing Downstream of Hanna
Road. See Figure 8.5. A low water crossing was installed downstream of
Hanna Road to provide access to a Valley Park public park. The low water
8-11
crossing has constricted the low flow channel with virtually no sediment
transport capacity. This induced sediment deposition and accelerated
lateral migration from the low water crossing upstream to Hanna Road.
The low water crossing has significantly destabilized this reach and must
be removed. We recommend replacing the low water crossing with an
elevated pedestrian bridge. Sediment transport capacity through the reach
from Hanna to the pedestrian bridge can be restored with a series of rock
weirs and guide vanes. The weirs and guide vanes can also help reduce
bank erosion through this reach by lowering near-bank shear stress. We
also recommend urban forestry on the several acres of riparian corridor to
remove the invasive vegetation and improve corridor health and habitat.
•
319MS31 – Sediment Transport Monitoring, Holly Green Confluence to
Vance Road. See Figures 8.5 and 8.6. The reach of main stem Fishpot
Creek from the Holly Green tributary confluence to the Vance Road
crossing will react and adjust to changes in the sediment regime. The
recommended interventions throughout the watershed upstream of this
reach will reduce the amount of sediment being delivered. The
recommended alterations in sediment transport competency within this
reach will change how sediment moves through the lower part of the main
stem. The reach upstream of Hanna Road contains both stable reaches
and actively migrating reaches. The migration is influenced by low bed
slope, poor sediment transport competency and high sediment supply.
The reach from the Valley Park Tributary downstream to Vance Road is
stable in profile with a tendency toward meander migration, influenced by
sediment supply, low bed slope, and Meramec River backwater.
We recommend semi annual monitoring of this reach to identify stream
response to watershed interventions.
Red Start Tributary
•
319RS1 – Monitoring Red Start Tributary. See Figure 8.2. In the lower
portion of Red Start Tributary several knick points occur in a reach of
stream that is largely bedrock controlled. Channel incision is the dominant
fluvial process through this reach, although the bedrock outcrops appear
to have greatly slowed the incision from proceeding upstream. While the
tributary is laterally stable, it should be monitored for changes in the
channel shape or aggravation of channel incision in response to future
land use changes.
8-12
Larkhill Tributary (SSMIP Branch D)
•
319LH1 – Winchester Detention Pond. See Figure 8.3. FIS-29 addresses
the problem of potential flooding in Winchester with the recommendation
of upstream stormwater storage. According to the SSMIP:
“This option included creation of a 2-acre pond with capacity
to provide 5 feet of live storage or (10-acre-feet). An outlet
structure sized so as to limit discharges to the capacity of the
downstream 48-inch sewer will also be provided. This site is
in a developing commercial area so has some potential
business use. Although this is the least expensive and
preferred solution, timing and development pressure may
make the window of opportunity rather short.”
The City reports that the pipe may be clogged because of debris flow
generated from upstream. Debris management and prevention should be
specifically addressed in the design. We concur with the existing FIS-29
recommendation.
Boleyn Tributary
See Figure 8.4. The Boleyn Tributary is laterally stable, alternating between
sediment transport and deposition, with a minor knick zone downstream of
Winding Path Lane. Channel adjustments that we observed were minor and did
not pose a foreseeable threat to property or infrastructure. We have no
management recommendations for the Boleyn Tributary.
Bromfield Tributary (SSMIP Branch C)
•
319BF1 – Grade Stabilization and Two Stage Channel. See Figure 8.4.
Advancing channel incision threatens to undermine gabion and modular
block bank armoring along Bromfield Tributary, upstream (East) of Hanna
Road. Channel incision has already exposed a sanitary sewer line
crossing. The headwaters of the Broomfield tributary begin at two storm
outfalls west of Briarhust. The channels downstream of the outfalls are
short. Both channels and the confluence into the Bromfield Tributary are
armored with dumped concrete rubble and rock. The channel has been
severely constricted on the left descending bank downstream of the
headwaters confluence. Evidence of past incision and inadequate existing
channel shape and function is clear.
We recommend installing in-stream weirs to guide flow and control grade.
We also recommend reshaping the channel to a functional low flow
channel section and constructing a bank full flood plain to provide
hydraulic relief during large storm events. The project reach should
8-13
extend from the exposed sewer crossing at the downstream end to the
headwaters confluence at the upstream end.
•
319BF2 – Channel Interventions and Urban Forestry. See Figure 8.4.
The reach downstream of Hanna Road is actively eroding. The scour hole
at the Hanna Road culvert outfall is over six feet deep and has eroded
beneath the culvert toe wall. There is strong evidence of lateral migration
undermining existing gabion structures and eroding both banks
downstream of Hanna Road. There are several active failures along the
high left descending banks. A significant vine and honeysuckle problem
has damaged the riparian corridor for nearly the entire length. Existing
gabions are aggravating the problem by amplifying the erosive forces.
We recommend removing the existing gabions and stabilizing this reach
through a combination of grade controls, weirs and a two-stage channel.
Many of the gabions on the right descending bank constrict the channel
and create scour at the gabion toe. The high-energy conditions causing
erosion and steep left descending banks can be addressed through
turning vanes and a cross section shape designed to reduce shear stress.
Adequate common ground exists to install a two-stage channel for the
entire reach. In addition, we recommend urban forestry for the entire
length to restore a healthy riparian corridor.
Holly Garden to Big Bend Reach
•
319HG1 – Scour Pool and Drop Structure Downstream of Holly Garden
Court. See Figure 8.8. The dominant fluvial process downstream of Holly
Garden Court is channel incision. There is a scour pool at the Holly
Garden Court culvert outfall. The channel downstream of the scour pool is
incising and the existing grouted rip rap has collapsed. A sanitary sewer
pipe is exposed in the bed approximately 50 feet downstream of the Holly
Garden Culvert outfall. We recommend an armored scour pool at the
culvert outfall to dissipate the energy of water exiting the culvert. Further,
we recommend removing debris and concrete from the channel between
the scour pool and the exposed sanitary line. We also recommend
placing a grade control or drop structure immediately downstream of the
sanitary line.
•
319HG2 – Scour Pool Downstream of Brightfield Drive. See Figure 8.8.
There are several interventions downstream of the Brightfield Drive
Culvert. The channel is lined with Reno mattresses at the culvert outfall
with gabions on the right descending bank. Proceeding downstream, the
channel lining changed from Reno mattress to grouted rip rap. There is a
three foot deep scour pool immediately downstream of the grouted rip rap.
The grouted rip rap is undermined and failing. From our observations it
8-14
appears that the grouted rip rap was constructed in reaction to the scour
pool at the end of the Reno mattresses. Channel widening is the dominant
process downstream of the culvert. The scour is caused by the failure to
construct adequate energy dissipation downstream of the high energy
culvert outfall and transitioning to the natural channel. Previous attempts
have failed because they armor the bed and bank without dissipating the
energy. This simply shifts the high energy further downstream.
We recommend constructing a scour pool immediately downstream of the
grouted rip rap-lined section to dissipate the energy. We also recommend
breaking up the grouted rip rap into angular pieces and planting the reach
with appropriate riparian species.
•
319HG3 – Urban Forestry and Rock Weirs along Holly Berry Drive. See
Figure 8.7. Widening is the dominant process between Brightfield Drive
and the confluence with New Ballwin Tributary. The channel is generally
stable in profile with some areas of deposition. We recommend urban
forestry to restore the riparian corridor and stabilize the eroding left
descending bank behind homes along Holly Berry Drive with a series of
weirs.
•
319HG4 – Grade Control Exposed Sanitary Sewer at Holly Berry Drive
See Figure 8.7. Again, the dominant fluvial process upstream of the New
Ballwin Tributary confluence is widening. There are two exposed sewer
lines in the channel bed upstream of the confluence. We recommend
installing rock weirs at the sewer line crossings to direct flow, protect the
existing pipes, and prevent continued channel widening at these locations.
This intervention is separate from 319HG3 – Urban Forestry and Rock
Weirs along Holly Berry Drive because sanitary lateral protection is a
higher priority and a separate objective. 319HG4 can be done in
combination with 319HG3.
•
319HG5 –Big Bend Road Culvert. See Figure 8.7. Immediately upstream
of the Big Bend Road culvert, the Holly Green Tributary is depositional
and stable in plan form. The box culvert at Big Bend Road is presently
acting as a de facto grade control. The hydraulic analysis indicates
overtopping of Big Bend Road by the 100-year flood. This flooding is most
likely aggravated by the accumulation of bed material and debris upstream
of the culvert. From field observations it is apparent that the Big Bend
culvert was initially constructed about three feet too low for the stream
conditions upstream. This initiated a three-foot head cut that propagated
upstream. However, the reach upstream of Big Bend Road has since
recovered from channel incision and is now undergoing channel widening.
Removing the culvert or constructing an additional 8’ x 10’ culvert opening
at the existing culvert sill elevation would propagate another wave of
8-15
channel incision and potentially destabilize the recovered reach upstream
of the existing culvert.
We recommend putting a nose on the center pier of the existing double
box culvert. In addition, flanking culverts could be added on either side,
elevated about four feet above the existing culverts’ flowline, to improve
conveyance during bankfull flow without altering normal fluvial process
during low flow conditions. The design should include sizing the flanking
culverts.
Big Bend to Main Stem Confluence Reach
•
319HG6 – Erosion Control Along Cascade Terrace Drive. See Figure 8.7.
This reach extends from an existing five to six foot knick point in bedrock
downstream of Big Bend Road to a 200 foot long rip rap intervention on
the left descending bank several hundred feet downstream of the knick
point. This is a transport reach that is widening and migrating during high
flows. We recommend weirs and guide vanes to reduce erosion and
subsequent sediment generation through this reach.
•
319HG7 – Erosion Control Downstream of Arbor Crest Drive See Figure
8.7. This reach extends approximately 1,000 feet beginning upstream at a
six to seven foot knick point in bedrock near Arbor Crest Drive. There is a
30-inch VCP sanitary line exposed in the left descending bank at the lower
end of this reach. The dominant processes in this reach are widening and
meander migration. We noted that a large amount of chert bed load is
being generated here. We recommend weirs and guide vanes to reduce
erosion and subsequent sediment generation through this reach and to
protect the exposed sanitary line.
•
319HG8 – Channel Migration Monitoring Near Elm Crossing Court. See
Figure 8.7. This reach of the Holly Green Tributary is generally stable,
both vertically and laterally. However, localized channel migration in the
vicinity of the landfill at the top of the right descending bank should be
monitored.
•
319NB1 - Guide Vanes at Turfwood Drive. See Figure 8.8. At the
upstream end of New Ballwin Tributary, downstream of the outlet at New
Ballwin Road, the dominant process is meander migration. Interventions
are necessary to control the migration threatening property along
Turfwood Drive. Although the left descending bank is tall and eroding, the
stream can access the right descending bank though apparently not with
sufficient frequency to reduce the erosive stress. Guide vanes should be
8-16
installed along the left descending bank, allowing the stream to adjust its
course in the direction of the largely undeveloped right descending bank.
•
319NB2 – Erosion Control and Raise Channel at Great Hill Drive. See
Figure 8.8. At a sharp meander bend around Great Hill Drive, channel
incision is the dominant process, evidenced by a knick zone through
resistant chert and limestone bed material. The propagation of incision
has led to bank failures that currently threaten residential property on
Walnut Point Court, Great Hill Drive, and Rustic Valley Court. An existing
ductile iron pipe crosses the channel seven feet above the flowline of the
bed. This indicates the degree of past incision. The incision in this reach
and the subsequent generation of significant sediment loads has important
implications throughout the system. Locally, the incision will cause the
loss of many large trees as they are undermined and fall into the channel.
We recommend raising the bed through this reach and reconstructing a
stable and functional two stage channel in combination with grade controls
to stop future incision. This can be accomplished through a series of grade
controlling weirs and short drop structures. The intervention should start
upstream of the meander switchback at Walnut Point Court. The huge
influx of sediment and coarse material generated by this reach is a
primary management concern for the downstream reaches.
•
319NB3 – Grade Control Towerwood Confluence. See Figure 8.8. There
is a knick zone in the New Ballwin Tributary immediately upstream of the
confluence of Tower Wood tributary. The process in this reach is incision.
We recommend a grade control to arrest the incision. Since the Tower
Wood Tributary is also incising and the New Ballwin knick point is close to
the confluence, we recommend placing the grade control immediately
downstream of the confluence thereby controlling incision in both
tributaries with one structure.
•
319NB4 – Grade Control Exposed Sewer Line Upstream of Rustic Valley
Drive Culvert. See Figure 8.8. Immediately upstream of the Rustic Valley
Drive culvert an undermined ten-inch ductile iron sanitary line marks the
location of another knick point advancing upstream. The exposed pipe is
acting as a flat weir perched about 1.5 to two feet above the channel bed.
We recommend a grade control immediately downstream of the sanitary
crossing to restore grade, protect the sanitary line and control future
incision.
•
319NB5 – Rock Toe at 504 Vernal Hill Court. See Figure 8.8. There is a
compliant of bank erosion threatening a structure at #504 Vernal Hill
Court. This is located on the right descending bank immediately
downstream of the Rustic Valley Drive culvert outfall. The erosion is not
8-17
severe. We recommend a vegetated rock toe to reduce erosive near-bank
shear stress.
•
319NB6 – Monitoring Along Vernal Hill Court. See Figure 8.8. The
dominant fluvial process along Vernal Hill Court downstream of Rustic
Valley Drive is plan form alteration. Depending on the location in the
reach this manifests as either minor widening or meandering. Minor
erosion is flanking a 1.5foot high railroad tie wall at one residence towards
the downstream end of this reach. We recommend monitoring the reach
along Vernal Hill Court.
•
319NB7 – Grade Control Exposed Sewer Line and Rock Toe High Bank at
Briarhill Court. See Figure 8.8. There are complaints of bank erosion
threatening structures at #567 and #568 Vernal Hill Court. The dominant
fluvial process in this reach is widening with indication of past incision.
We also noted some local lateral migration. The previous incision has
resulted in bank failures and an existing sanitary line is exposed in the bed
and a sanitary manhole is exposed on the left descending bank behind
Briarhill Court. The channel is widening downstream of the sanitary line.
We recommend a grade control immediately downstream of the exposed
sanitary line to prevent further erosion and undermining of the sewer line.
The high bank behind Briarhill Court is retreating and undermining a
number of trees that will eventually fall into the channel. To prevent this
and to protect the manhole, we recommend armoring the bank toe,
installing a second grade control for this reach, possibly raising the bed
one foot, and re-grading the top of the bank.
•
319NB8 – Confluence Grade Control at Ferris Park and New Ballwin
Tributaries. See Figure 8.7. Approximately 500 feet downstream of Mark
Wesley Lane the Ferris Park Tributary empties into the New Ballwin
Tributary from the right descending bank. The channels are widening and
depositional at the confluence. About 50 feet upstream from the
confluence is a grout-encased sanitary crossing restraining a knick point.
We recommend constructing a grade control downstream of the
confluence to focus flow and mitigate widening of both channels at this
location. The weir should also be designed to manage grade at the
confluence to protect both tributaries from potential future waves of
incision.
•
319NB9 – Bank Stabilization at Reis Road. See Figure 8.7. New Ballwin
Tributary is a depositional reach undergoing meander migration at Reis
Road. The left descending box of the Reis Road culvert has lost nearly
one-quarter of its flood capacity due to deposition. Currently, the scour on
the right descending box has exposed a storm line. We recommend
improving the approach to the Reis Road culvert by constructing a weir to
8-18
guide the flow into one of the boxes and provide sufficient head to keep
the other box clean and functional during high flows. The weir will allow
the new culvert to more closely preserve the natural dominant discharge
stream geometry through the culvert by eliminating the over widened low
flow channel. We also recommend stabilizing the meandering upstream
reach with a combination of weirs, rock toe protection and urban forestry.
•
319NB10 – Bank Stabilization and Urban Forestry Upstream of Old
Ballwin Tributary Confluence. See Figure 8.7. The reach along the north
side of the church at the intersection of Big Bend and Reis Road is
depositional. As is common in similar reaches, the deposition has induced
changes in channel planform manifested as widening or meander
migration, depending on the location in the reach. The widening is not
severe but the building is close to the stream bank and the riparian
corridor has been removed. The root matrix associated with a healthy
riparian corridor strengthens the stream bank which is useful in a widening
and migrating reach. We recommend replanting the riparian corridor in
combination with rock toe along the right descending bank and urban
forestry.
•
319OB1 – Grade Control Knick Zone along Golfwood Drive. See Figure
8.8. The reach along Golfwood Drive between Bitterwood Drive and
Blazedwood Drive is widening and actively plucking bedrock. We
recommend installing grade controls to control future incision and weirs to
reduce lateral migration.
•
319OB2 – Grade Control Incising Reach and Protect Sanitary Sewer
Downstream of Talbert Court. See Figure 8.8. The reach immediately
downstream of the Talbert Court culvert is actively incising. This is classic
active incision characterized by a narrow channel with high lower limit of
woody vegetation and raw lower banks. The incision has exposed a
sanitary line. We recommend grade controlling the reach to halt incision
and protect the sanitary line.
•
319FP1 – Grade Control Ferris Park Tributary. See Figure 8.8. The reach
from Nanceen Court to Mark Wesley Lane is actively incising. At some
locations, post incision widening is also evident. There are two distinct
knick points, a three foot drop at a grouted rip rap crossing near Clear
Creek Court and another two foot drop near Wynn Place. We recommend
grade controlling the knick points and installing intermediate weirs to
control lateral adjustments.
8-19
Towerwood Tributary
•
319TW1 – Grade Control Upstream of Great Hills Drive. See Figure 8.8.
Upstream of Great Hill Drive, Towerwood Tributary is incising and bank
heights are increasing. We recommend lowering bank heights and
controlling incision through a series of grade controls. This reach is
generating sediment for delivery downstream.
•
319TW2 – Drop Structure Downstream of Great Hills Drive. See Figure
8.8. The Tower Wood tributary between Great Hill Drive and the
confluence was once a detention pond. The detention pond was breached
and the existing confluence is about three feet lower than the concrete
bottom channel that was the detention pond low flow channel. We
recommend either a new detention pond berm and outfall structure or
installing a drop structure to manage the grade change between the
Towerwood Tributary and the New Ballwin Tributary.
•
319VP1 – Crescent Road Two Stage Culvert. See Figure 8.6. The
existing hydraulic model indicates the Crescent Road culvert is
overtopped by the 2-year flood level. We recommend replacing the
existing 4 x 6 foot culvert with a twin barrel, two stage culvert. One barrel
would accommodate low flow, while the other barrel would be installed at
bankfull elevation to accommodate high flows.
•
319VP2 – Elevate and Grade Stabilize Crescent Valley Court Reach. See
Figure 8.6. The reach immediately downstream of Crescent Road has
incised and undermined the grouted riprap bank armoring along Crescent
Valley Court. The banks are now at or over 10 feet and approaching their
critical height. Failure appears imminent. We recommend raising the bed
along 500 feet of channel downstream of Crescent Road. The elevation
change between the existing bed and the new raised reach can be
accomplished with energy dissipating drop structures. Once the bed has
been raised, we recommend a two-stage channel to manage fluvial
process through all flows.
•
319VP3 – Grade Control Sewer Crossing. See Figure 8.6. A grouted
sanitary sewer crossing is holding a three-foot knick point near Crescent
Ridge Drive. The grout appears to be in good condition, but the sewer line
could be undermined. We recommend a grade control and energy
dissipater immediately downstream of the sewer crossing to
accommodate the three foot drop in grade.
8-20
•
319VP4 – Monitoring of Valley Park Tributary. See Figure 8.6. A large
log jam near Crescent Ridge Drive is acting as a grade control. The log
jam appears stable, but should be monitored to insure that it continues to
maintain channel grade. Since the Valley Park Tributary is relatively short,
we recommend monitoring the entire tributary on a semi annual basis. The
monitoring would involve walking the entire reach and summarizing
significant findings in a brief observation memorandum.
The meandering reach of the Valley Park Tributary downstream of 319VP4 does
not pose any foreseeable threat to property, infrastructure, or the upstream
stability of this tributary. In addition, there is a wide riparian corridor and
floodplain on either side of the channel. For these reasons, we suggest that this
reach should be allowed to adjust in plan form, without intervention, so that a
stable meander pattern can develop.
8-21
9.0 PROJECT COSTS
The opinions of probable project costs are divided into three cost centers as
follows:
1. Survey costs
2. Engineering design and construction observation costs
3. Construction costs
Survey Costs
Long profile (longitudinal profile) survey. The long profile survey is a profile
survey of the channel thalweg. Ideally long profiles are conducted on a
watershed or sub-watershed scale. If this is not possible, the long profile survey
must extend from one geomorphic hard point to another thereby encompassing a
geomorphically isolated reach. Geomorphic hard points are areas where the
stream position is locked in both plan and profile. These include culverts or
streams embedded in durable rock outcrops.
The long profile is one of the essential analytical tools for final design of any
stream intervention. The designer will compare the profiles to field observations
to determine both local stability and predict effect of structural alterations. The
survey is also necessary to evaluate significant changes in bed elevations that
occur after this report is issued. Re-evaluation of the mobility of knick points and
migrating banks are especially important for detailed design when positioning
grade control and energy management structures. The potential location of
these structures can change significantly in a few years time, therefore; failure to
re-survey the long profile may produce an ineffective design. From the relatively
simple data of the profile, the final designer can also determine how the stream is
transporting sediment and isolate sites of poor transport as well as determine
stable plan form geometry.
Boundary and topographic survey. Topographic surveying of the channel and
surrounding property is necessary for precise design location and calculations,
construction quantities, utility locations, etc. Temporary construction easements
and drainage easements are based on the boundary survey. Typically, the final
topographic and boundary survey limits are determined after the long profile
survey has been analyzed and the final design structures have been located.
As-Built Survey. The as-built survey is necessary to locate structures in place
after the project has been constructed. This is final proof for the City and
designer that the structures were installed according to plans and grades.
Engineering Design and Construction Observation Costs
Engineering Design and construction observation opinions include costs for
design calculations, design plans, specifications, contract documents, agency
9-1
submittal documents, easement preparation and more. The design calculation
costs vary depending on the length of reach being analyzed, type of systemic
problem being addressed by the design, type of structure, number of structures
and interaction of the structures to be designed. There is a basic amount of
analysis and knowledge required for all designs, no matter how small. To design
just one small guide vane, a designer must still thoroughly understand the
dominant fluvial properties of the reach.
Engineering design and construction observation cost opinions are based on the
following services to be provided by a professional river engineer:
Engineering background and field data collection, reduction, analysis and design.
The engineering design cost opinion is based on current practices in stormwater,
river and stream engineering. This assumes fluvial geomorphology and natural
channel design methodologies will be used to guide civil engineering design
involving natural stormwater systems. Some of the engineering background and
field data collection, reduction, analysis and design functions are:
•
Geotechnical Analysis: The analysis will include traditional soil parameters
such as effective cohesion,Φ, grain size, and plasticity index. Moreover,
slope stability analysis for stream banks differs considerably from those
appropriate for slopes of dams or earth embankments. Slope stability
analysis includes both fluvial and geotechnical influences. The cost estimate
assumes use of standard methods to evaluate the influence of root
reinforcement on shear strength as well as temporal and spatial variability of
the water table. We also assume that the designer will consider soil
erodibility parameters in conjunction with the calculated hydraulic shear to
determine toe and bed resistance to scour for critical flows.
•
Sediment Transport: Sediment transport competency and stream power must
be analyzed and the results used to guide the scour, incision and deposition
design. The cost estimate assumes that local sediment transport competency
will be evaluated during design, but a detailed sediment transport analysis
with the extensive collection of field data, over an extended time period will
not be performed. The cost estimate also assumes a sediment transport
model will not be developed.
•
Hydraulics: In addition to evaluating water surface elevations, hydraulic
analysis is required to determine rock size and shear stress on bed, bank and
vegetation. A no-rise certificate is required for FIS streams. The cost estimate
assumes that existing HECRAS models will be modified and that additional
hydraulic calculations will be performed. The cost estimate does not include
preparation of LOMR, LOMA or similar documents.
9-2
•
Soil Bioengineering: Soil Bioengineering is an important component of Natural
Channel Design. Soil bioengineering is not used as a bank stabilization
technique in the absence of a larger river stability context. In preparing soil
bioengineering designs we assume that the designer will incorporate
hydraulic, hydrologic, geotechnical and fluvial geomorphologic data in the
selection of technique and plants. In the cost estimate, we assume that the
designer has access to a site-adapted database of plant materials including
mechanical properties as well as cultural requirements, habitat values and
aesthetic values.
•
River Engineering: The river engineer must combine the results of the
geotechnical evaluation, slope stability, erosion and scour potential, sediment
transport, hydraulic analysis and soil bioengineering results into a
comprehensive design.
•
Prepare Contract Documents: In preparing the cost opinions that follow, we
made several assumptions. They include preparation of the contract
documents using approved formats and inclusion of the final design plans and
specifications in the contract documents. The final design plans and
specifications cost opinions are based on the following general plan format
and deliverables.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
The final format will be specified by the final owner.
Title sheet with legend, index and location map.
Summary of Quantities sheet.
Plan Profile sheets at 1”=20’ horizontal scale and 1”=5’ vertical scale.
Planting Plan and Planting Palette sheet(s).
Cross-Section sheets with cross-sections at a minimum of 50’
intervals.
Erosion and Sediment Control sheet.
Detail sheets.
Location and elevation of project benchmark.
Final engineer’s opinion of construction cost.
Reproduction of bid documents and specifications
1 set of plans on reproducible mylars.
Necessary drainage and temporary construction easement plats and
scripts.
Easement Plats and Scripts: The potential number and location of easements
were taken from the electronic parcel map provided for this analysis. The
number of effected parcels was assumed based on the location and extent of
interventions and proximity to nearby property boundaries.
9-3
•
Permitting: Preparing and submitting applications for Section 404 and Section
401 of the Clean Water Act are included in the engineering design and
construction observation cost opinions.
•
Meetings: Several meetings are typically necessary during the design
process. The cost estimate for public meetings is greater for the larger
projects with many nearby affected residents. The increase for larger projects
is due to additional preparation time and additional design professionals
possibly required in attendance for the large project public meetings. Design
costs were based on the assumption of the following meetings:
•
•
•
•
•
•
Project kickoff meeting.
Preliminary plan submittal review meeting.
90% design review meeting.
Final design review and approval meeting.
Other miscellaneous meetings based on the size of the project.
Public meetings and/or meetings with effected streamside residents as
necessary.
Construction Costs
Construction costs are divided into standard quantifiable cost items. The unit
costs for each cost item are estimated using similar costs from previous jobs in
conjunction with material wholesaler estimates and include the cost of materials,
equipment and labor for each item. Construction costs opinions are based on
concept level pre-design estimates of the following items:
•
•
•
•
•
•
•
•
•
•
Excavation
Embankment in Place
Clearing Grubbing and Debris Removal
Urban Forestry and Tree Protection
Erosion and Sediment Control
Energy Management Structures: This includes: guide vanes, rock weirs,
step pools, scour pools, etc.
Slope Stabilization: This includes vegetated composite revetments,
planted rock, and other slope treatments for higher energy environment.
Plants: The plants are for any planted structure and for site restoration
after construction. Plant costs include trees, shrubs, grasses and forbs in
ball and burlap, container, bare root, or seed as appropriate for each
intervention.
Restoration: Restoring access and disturbed areas not otherwise included
in other items.
Pavement: This is for roadway, driveway, sidewalk or trail improvement,
rebuilding or relocation as a result of the project.
9-4
•
•
•
•
•
•
Storm Manholes
Class III Reinforced Concrete Pipe
Box Culvert
Bridges: this item includes the removal of existing bridge or culverts.
Structure Removal: This is for the removal of significant structures such as
bridges, culverts, headwalls, etc. not otherwise included in previous cost
items.
Mobilization and Bond
A 15% contingency was added to the cost opinion because of the preliminary
nature of the cost data.
We are aware that some of these construction methods may be unfamiliar to
local contractors. In our experience, the first few projects using Natural Channel
Design methods in a region are more expensive than similar projects in
communities where these methods are more established. Fortunately, market
forces quickly intervene as experienced contractors from other regions compete
for local work or as more entrepreneurial local contractors choose to make
natural channel projects their specialty.
Table 9.0 shows the estimated total cost and the associated surveying,
engineering and construction cost for each 319 proposed project. Detailed cost
sheets are presented in Appendix E.
9-5
Table 9.0 Project Cost Opinions
319 Project Description
Surveying
319MS01 – Guide Vanes at Field Avenue
319MS02 – Grade Stabilization and Sewer Lateral Protection
319MS03 – Bankfull Floodplain Downstream of Fairview Drive Bridge
319MS04 – Re-shape De facto Turning Vane
319MS05 – Flood Proof Homes
319MS06 – Relocate Utility Lines on Eroding Bank
319MS07 – Armored Scour Pool, Bank, and Bed Protection
319MS08 – Bankfull Floodplain and West Skyline Bridge
319MS09 – Smith Drive Bridge
319MS10 – Manchester Road Bridge
319MS11 – Reinforce Existing Knick point
319MS12 – Floodproof Structures at Old Ballwin Road
319MS13 – Protect Sanitary Line
319MS14 – Add Bankfull Flow Capacity at Ramsey Lane
319MS15 – Weirs Upstream of Reis Road
319MS16 – Reis Road Bridge
319MS17 – Bankfull Floodplain between Reis Road and Lindy Drive
$
$
$
$
Engineering
Construction
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
85,400
275,800
398,000
85,400
83,000
19,000
137,900
1,229,500
788,600
1,866,900
85,400
125,000
85,400
569,500
285,000
1,187,200
2,612,600
$
$
$
$
$
$
35,300 $
45,000
$
67,000 $
192,200
$
55,300 $
326,600
$
29,700 $
47,600
Used FIS-18 Cost
- $
- $
19,000
8,700 $
43,600 $
85,600
25,300 $
168,200 $
1,036,000
14,700 $
121,300 $
652,600
29,400 $
117,300 $
1,720,200
7,800 $
38,200 $
39,400
Used FIS-09 and partial FIS-08 Cost
7,800 $
38,200 $
39,400
22,500 $
110,100 $
436,900
21,600 $
69,600 $
193,800
25,300 $
123,300 $
1,038,600
64,400 $
188,500 $
2,359,700
319MS18 – Lower Exposed Sewer Lines Between Reis and Lindy Drive
319MS19 – Bankfull Floodplain between Lindy Drive and Sulphur Springs Road
$
Currently in MSD Design
28,300 $
108,000 $
1,381,000 $
1,517,300
319MS20 – Replacement of Aerial Sewer Line at Chappel Court
319MS21 – Analysis of Sulphur Springs Approach and Knick zone
319MS22 – Turning Vanes Upstream of the Wren Avenue Culvert
319MS23 – Turning Vanes Downstream of the Wren Avenue Culvert
319MS24 – Meander Migration Monitoring, Upstream of Big Bend Road
319MS25 – Protect Stratford Ridge High Bank
319MS26 – Protect High Bank Downstream of Stratford Ridge
319MS27 – Guide Vanes at Main Stem and Holly Green Confluence
319MS28 – Pepperdine Reach Bank Stabilization
319MS29 – Hanna Road Bridge Improvement
$
$
$
$
$
$
$
$
$
Currently in MSD Design
8,100 $
45,800 $
16,100 $
63,900 $
6,400 $
40,000 $
3,500 $
900 $
26,700 $
61,300 $
21,600 $
52,300 $
21,600 $
54,500 $
35,900 $
65,000 $
39,100 $
146,400 $
88,100
221,000
62,100
408,000
83,600
161,800
312,000
2,147,300
$
$
$
$
$
$
$
$
$
142,000
301,000
108,500
4,400
496,000
157,500
237,900
412,900
2,332,800
$
$
$
$
$
$
9-6
5,100
16,600
16,100
8,100
Total
Surveying
319MS30 – Remove the Low Water Crossing Downstream of Hanna Road
319MS31 – Sediment Transport Monitoring, Holly Green Confluence to Vance Road
319BF1 – Grade Stabilization and Two Stage Channel
319BF2 – Channel Interventions and Urban Forestry
319FP1 – Grade Control Ferris Park Tributary
319HG1 – Scour Pool & Drop Structure Downstream of Holly Garden Court
319HG2 – Scour Pool Downstream of Brightfield Drive
319HG3 – Urban Forestry and Rock Weirs Along Holly Berry Drive
319HG5 – Big Bend Road Culvert
319HG6 – Erosion Control Along Cascade Terrace Drive
319HG7 – Erosion Control Downstream of Arbor Crest Drive
319HG8 – Channel Migration Monitoring Near Elm Crossing Court
319LH1 – Winchester Detention Pond
319NB01 – Guide Vanes at Turfwood Drive
319NB02 – Erosion Control and Raise Channel at Great Hill Drive
319NB03 – Grade Control Towerwood Confluence
319NB04 – Grade Control Exposed Sewer Line Upstream of Rustic Valley Drive Culvert
319NB05 – Rock Toe at 504 Vernal Hill Court
319NB06 – Monitoring Along Vernal Hill Court
319NB07 – Grade Control Exposed Sewer and Rock Toe High Bank at Briarhill Court
319NB08 – Confluence Grade Control at Ferris Park and New Ballwin Tributaries
319NB09 – Bank Stabilization at Reis Road
319NB10 – Bank Stabilization and Urban Forestry Upstream of Old Ballwin Tributary Confluence
319OB1 – Grade Control Knick Zone along Golfwood Drive
319OB2 – Grade Control Incising Reach and Protect Sanitary Sewer Downstream of Talbert Court
319RS1 – Monitoring Red Start Tributary
319TW1 – Grade Control Upstream of Great Hills Drive
319TW2 – Drop Structure Downstream of Great Hills Drive
9-7
$
$
$
$
$
$
$
$
$
$
$
$
$
31,100
12,900
39,100
32,200
5,800
5,800
23,000
9,700
11,700
23,000
23,700
-
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
8,100
29,900
9,700
9,700
9,700
6,000
7,400
16,100
12,200
12,200
12,200
15,000
9,400
Engineering
$
109,700 $
$
12,400 $
$
62,600 $
$
91,400 $
$
92,100 $
$
37,800 $
$
38,300 $
$
62,700 $
$
34,000 $
$
60,500 $
$
66,900 $
$
72,500 $
$
5,500 $
Used FIS-29 Cost
$
57,200 $
$
107,100 $
$
35,900 $
$
35,200 $
$
35,200 $
$
5,500 $
$
38,200 $
$
7,400 $
$
66,600 $
$
51,800 $
$
57,300 $
$
51,900 $
$
5,500 $
$
59,200 $
$
56,100 $
Construction
475,000
214,600
485,100
357,100
40,100
41,600
177,600
26,500
193,700
388,400
458,300
154,200
748,800
56,800
55,500
50,800
69,900
53,800
165,600
90,300
114,200
71,900
80,200
104,400
Total
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
615,800
12,400
290,100
615,600
481,400
83,700
85,700
263,300
70,200
265,900
478,300
554,500
5,500
362,000
219,500
885,800
102,400
100,400
95,700
5,500
114,100
68,600
248,300
154,300
183,700
136,000
5,500
154,400
169,900
Surveying
Engineering
Construction
Total
319VP1 – Crescent Road Two Stage Culvert
319VP2 – Elevate and Grade Stabilize Crescent Valley Court Reach
319VP3 – Grade Control Sewer Crossing
$
$
$
7,400 $
15,000 $
9,700 $
57,700 $
58,100 $
34,000 $
193,400 $
246,900 $
26,500 $
258,500
320,000
70,200
319VP4 – Monitoring of Valley Park Tributary
$
- $
5,900 $
- $
5,900
$
888,400 $
3,415,900 $
TOTAL COST
9-8
18,238,700
$
23,113,000
10.0 MASTER PROJECT TABLES
Following are three Master Project Tables presenting each 319 proposed project with the project description, priority, and
cost. The projects are sorted first by priority in Table 10.0, then by location in table 10.1, and finally by cost in table 10.2.
Table 10.0 lists the proposed 319 projects in order of highest priority.
Table 10.0 Projects by Priority
Priority
319MS02 – Grade Stabilization and Sewer Lateral Protection
319MS10 – Manchester Road Bridge
319MS21 – Analysis of Sulphur Springs Approach and Knick Zone
10-1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Total
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
290,100
83,700
70,200
362,000
275,800
19,000
1,866,900
125,000
85,400
569,500
2,612,600
1,517,300
142,000
301,000
412,900
2,332,800
100,400
114,100
136,000
258,500
Priority
1
Priority 1 Total Cost =
2
2
2
2
2
2
2
2
2
2
2
2
2
2
319MS11 – Reinforce Existing Knick Point
319NB01 – Guide Vanes at Turfwood Drive
3
3
3
3
3
3
3
3
3
10-2
Total
$
70,200
$11,745,400
$ 478,300
$ 554,500
$
85,400
$ 1,229,500
$ 788,600
$ 285,000
$ 1,187,200
$ 615,800
$ 885,800
$ 102,400
$ 248,300
$ 183,700
$ 154,400
$ 320,000
$ 7,118,900
$
$
$
$
$
$
$
$
$
615,600
481,400
265,900
398,000
85,400
496,000
157,500
237,900
219,500
Priority
3
3
3
3
319MS04 – Re-shape De facto Turning Vane
4
4
4
4
4
4
4
4
4
4
4
4
Total
$
$
$
$
68,600
154,300
5,500
5,900
$ 3,191,500
$
$
$
$
$
$
$
$
$
$
$
$
85,700
263,300
5,500
85,400
83,000
137,900
108,500
4,400
12,400
95,700
5,500
169,900
Priority 4 Total Cost = $ 1,057,200
10-3
Table 10.1 lists 319 proposed projects by location.
Table 10.1 Projects by Location
Fishpot Main Stem
319MS02 - Grade Stabilization and Sewer Lateral Protection
319MS10 - Manchester Road Bridge
319MS04– Re-shape De facto Turning Vane
10-4
Priority
Total
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
3
3
3
3
3
4
$ 275,800
$
19,000
$ 1,866,900
$ 125,000
$
85,400
$ 569,500
$ 2,612,600
$
$ 1,517,300
$
$ 142,000
$ 301,000
$ 412,900
$ 2,332,800
$
85,400
$ 1,229,500
$ 788,600
$ 285,000
$ 1,187,200
$ 615,800
$ 398,000
$
85,400
$ 496,000
$ 157,500
$ 237,900
$
85,400
Priority
4
4
4
4
4
Fishpot Main Stem Total Cost =
Bromfield Tributary
1
3
Bromfield Tributary Total Cost =
3
Ferris Park Tributary Total Cost =
Holly Green Tributary
1
1
2
2
3
4
4
4
Holly Green Tributary Total Cost =
10-5
Total
$
$
$
$
$
83,000
137,900
108,500
4,400
12,400
$16,258,100
$
$
290,100
615,600
$
905,700
$
481,400
$
481,400
$
$
$
$
$
$
$
$
83,700
70,200
478,300
554,500
265,900
85,700
263,300
5,500
$ 1,807,100
Priority
Total
Larkhill Tributary
1
Larkhill Tributary Total Cost =
319NB01 - Guide Vanes at Turfwood Drive
1
1
2
2
2
3
3
3
4
4
New Ballwin Tributary Total Cost =
1
2
Old Ballwin Tributary Total Cost =
$
362,000
$
362,000
$
$
$
$
$
$
$
$
$
$
100,400
114,100
885,800
102,400
248,300
219,500
68,600
154,300
95,700
5,500
$ 1,994,600
$
$
136,000
183,700
$
319,700
$
5,500
$
5,500
Red Start Tributary
3
Red Start Tributary Total Cost =
10-6
Priority
Towerwood Tributary
2
4
Towerwood Tributary Total Cost =
Valley Park Tributary
1
1
2
3
Valley Park Tributary Total Cost = $
10-7
Total
$
$
154,400
169,900
$
324,300
$
$
$
$
258,500
70,200
320,000
5,900
654,600
Table 10.2 lists the proposed 319 projects in order of total cost per project.
Table 10.2 Projects by Cost
Priority
319MS10 - Manchester Road Bridge
319MS02 - Grade Stabilization and Sewer Lateral Protection
10-8
1
1
1
1
2
2
2
2
2
3
1
2
3
3
2
1
3
1
2
1
1
2
1
3
4
1
2
Total
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
2,612,600
2,332,800
1,866,900
1,517,300
1,229,500
1,187,200
885,800
788,600
615,800
615,600
569,500
554,500
496,000
481,400
478,300
412,900
398,000
362,000
320,000
301,000
290,100
285,000
275,800
265,900
263,300
258,500
248,300
Priority
Total
319NB01 - Guide Vanes at Turfwood Drive
3
3
2
4
3
2
$
$
$
$
$
$
237,900
219,500
183,700
169,900
157,500
154,400
3
1
4
$
$
$
154,300
142,000
137,900
319MS04– Re-shape De facto Turning Vane
1
1
1
4
2
1
4
4
2
4
3
1
1
4
1
1
3
1
4
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
$
136,000
125,000
114,100
108,500
102,400
100,400
95,700
85,700
85,400
85,400
85,400
85,400
83,700
83,000
70,200
70,200
68,600
19,000
12,400
10-9
Priority
3
4
4
3
4
1
1
Total
$
$
$
$
$
$
$
5,900
5,500
5,500
5,500
4,400
-
Total Cost = $23,113,000
10-10
11.0 COMPARISON BETWEEN 319 PROJECT MASTER LIST AND SSMIP
PROJECTS
The dozens of flooding, erosion and infrastructure problems in the watershed
may appear unrelated. The SSMIP recommends treating these problems in
isolation; however, a more comprehensive analysis of the watershed reveals a
powerful linkage between problems from the headwaters to the mouth. The
headwaters tributaries, particularly those feeding Tributary B, are incising and
generating massive quantities of gravel for delivery to the main stem. Where the
stream has sufficient power to transport this bed load, there are relatively few
problems. However, at points of lower stream power, the bed load is deposited
in the streambed and in some cases contributes to flooding either by constricting
channels and culverts or by reducing the velocity of the water enough to raise
flow elevations. Throughout the watershed, excessive sediment deposition is
implicated in accelerated erosion including widening and meander migration.
This is particularly apparent in the lower reaches of the stream where delivery of
excess sediment generated by the tributaries drives accelerated meander
migration.
There is no mechanism to evaluate sedimentation and sediment transport
competency in the existing SSMIP hydraulic and hydrologic modeling. It is
simply not possible to manage Fishpot Creek for any purpose without managing
the movement of sediment through this system.
The geomorphic analysis is the required mechanism to diagnose the dominant
process driving instability in the Fishpot Creek Watershed. The hydraulic and
hydrologic models are the essential tools to quantify the flooding problem and
energy regimes in the system.
Recurring FIS Recommendations
There are two recurring recommendations in the FIS that are particularly
damaging to Fishpot Creek and its tributaries. Both hard armor lining and
channel widening address the symptoms of important problems. However, the
unintended consequences of these types of actions, as documented in
professional literature over the past fifty years, are often as bad as the problems
they were purported to solve. We recommend that neither hard channel lining
nor wholesale channel widening be implemented. Instead, we recommend a
series of treatments that address the complaints without propagating the problem
elsewhere in the watershed.
Gabion Lining on Eroding Banks. Gabion bank armoring is recommended as the
solution to bank erosion for eight SSMIP problems in reaches experiencing
channel incision or widening. In most cases, gabion lining is recommended in
reaction to a symptom without addressing the cause of the problem. Gabion
baskets temporarily armor the bank against high stream energy without resolving
11-1
the problem of erosive stream forces. An implicit assumption in any bank armor
tactic is that the stream is applying more stress to the banks than can be resisted
and that hardening the bank will remedy the problem. In the case of incision, the
stream is not applying excessive stress to the banks; it is the streambed that is
eroding in which case armoring the bank is counterproductive. In incising
streams, the bottom erodes out from under the gabion linings leaving them
perched and ineffective.
Gabions’ relative smoothness and near-vertical alignment increases the
magnitude of damaging forces. Fluid mechanics and shear stress analysis
illustrate that smooth, near-vertical surfaces substantially increase near surface
shear stress. Hard armor does not address the cause of bank erosion; it
concentrates and shifts the application of erosive stresses to another location.
Gabion baskets are also vulnerable to corrosion. Winter road salting sharply
elevates the chloride ion concentration in some urban streams. We have noted
baskets failed at the water line throughout St. Louis County. Once the lower tiers
of gabions corrode, the gabion rock is released into the stream to be transported
and deposited downstream. This sudden change in bed material typically
aggravates the initial problem of erosive stream power by re-setting the sediment
size and transport regime. This phenomenon is so common that Dr. David
Derrick, noted river specialist at the USACE ERDC, refers to gabions as “timedrelease bed load dispensers.” (Derrick, 2002) The loss of support from the lower
gabion tier leaves the upper gabions suspended above the channel which
sometimes results in the remaining baskets toppling into the channel. In many
cases, the toppled baskets act as a turning vane and direct the initial problem of
erosive stream flows towards the exposed soil behind the failed gabions.
A wider, smoother channel makes perfect sense from a hydraulic standpoint
alone, but is inappropriate for any stream system capable of adjusting its
boundaries. A better approach is to diagnose the process causing instability and
develop solutions that solve the problems by eliminating or mitigating the cause.
So instead of armoring against erosive forces, a more sustainable solution uses
natural stream form and function to reduce the erosive forces. A two-stage
channel is a preferred method to limit bed shear stress. Well vegetated banks
increase bank strength while decreasing near bank shear stresses and in-stream
structures redistribute shear stresses away from vulnerable locations.
Stream Widening to Increasing Culvert Capacity. Another common SSMIP
solution is to increase culvert capacity by adding barrels of the same height and
invert elevation to the existing culvert. Again, this may seem reasonable from a
hydraulic standpoint alone, but is inappropriate for a system capable of
responding to this action. If a channel is overwidened at the base, it will
immediately begin to fill in to re-establish a functional section shape. The over
widening induces a head cut upstream and potentially damaging deposition
downstream. This phenomenon has been thoroughly documented in the
11-2
stormwater engineering literature (Walesh, 1989) and commonly occurs
throughout St. Louis County.
The predictable process of the natural a stream rebuilding its low flow cross
section in response to over widening has the added consequence of reducing
culvert conveyance during high flows. The capacity is lost as the steam rebuilds
its bankfull shelf through the culvert. The success of the culvert design during
high flow events no doubt depends on full capacity. If the desired flood capacity
is lost, flood elevations upstream of the constriction will increase and damage
adjacent properties.
Incorporating the functional stream shape into culverts and under bridges will
eliminate the damaging cycle of erosion and deposition caused by over widening.
A two-stage channel through the culvert or under a bridge will accommodate
sediment transport and fluvial process for stream forming flows and provide the
required capacity during flood events.
The following is a comparison of the 29 SSMIP recommended projects and
corresponding 319 recommended projects. There are a total of 62 projects
recommended in this report. However, this section only reviews those 319
projects intended to address problems identified by the SSMIP projects or 319
projects that are addressing damage caused by a constructed SSMIP project.
The comparison follows each branch (main stem, then tributaries) from upstream
to downstream.
Fishpot Main Stem
Proceeding downstream from Clarkson Road, the first intervention is FIS-22:
Erosion of Bank Adjacent to Field Avenue. The problem is described as
erosion is threatening the roadway in vicinity of Field Avenue near Clarkson
Road. The recommended solution was to place gabions two tiers high on the left
bank for a distance of 60 feet.
A modular block wall was constructed at this location in place of the gabions.
Functionally, the two hard armor treatments have similar liabilities. The new
modular block wall on the left descending bank at Field Avenue is causing
erosion at the downstream end of the wall. The rip rap in the stream bed and
along right descending bank, across from the wall, is being flanked on the
upstream end. The damage created by the new wall generated project 319MS01
– Guide Vanes at Field Avenue which is the upstream-most, main stem 319
project.
The process in this reach is meander migration. The meander is migrating
downstream past the armored channel. As the channel migrates downstream it
is eroding the bank at the upstream end of the riprap and downstream end of
11-3
block wall. The increased stream energy created by the wall is aggravating the
erosion. The guide vanes will protect the upstream edge of riprap and
downstream edge of wall by guiding the stream through the bend.
The next two SSMIP interventions are FIS-21: Flooding of Two Homes
Upstream of Fairview Drive, FIS-20: Overtopping of Fairview Drive by 15Year Storm. The FIS 21 problem description is flooding of homes on both sides
of the channel by the 2-year storm. The recommendation is floodproofing the
homes. The FIS-20 problem description is inadequate capacity of the existing
structure (156 sq. ft. bridge opening). The recommendation is to increase
capacity by replacing the existing bridge structure with the equivalent of three 8foot by 12-foot parallel boxes.
Since the SSMIP was issued, a new 8ftX25ft Fairview Drive Bridge was built as
was a 200ft long, 10ft high modular block wall along the right descending bank
immediately upstream of Fairview Drive. We assume the new bridge and wall
were built to alleviate flooding through this reach. The natural channel width in
this reach is 12ft to 18ft wide. Upon the installation of the new Fairview Drive
Bridge, the channel was overwidened. As a result, a large volume of gravel and
sediment liberated from upstream of the culvert was transported downstream of
the new bridge and a new headcut began upstream of the new bridge.
The incision due to construction at Fairview generated 319 project 319MS02 Grade Stabilization and Sewer Lateral Protection. The process upstream of
Fairview Drive is channel incision. Several sewer laterals crossing the channel
have slowed propagation of channel incision. However, these crossings act as
flat weirs, collecting sediment and directing flow against both banks, resulting in
localized channel widening. The grade controls upstream of Fairview Drive will
protect the sewer laterals, control channel incision, relieve stress on banks, and
control sediment flow.
The next SSMIP recommendation is FIS-19: Flooding of Three Homes
Downstream of Fairview Drive. The problem description is flooding of two
homes by the 2-year storm and flooding of one by the 15-year storm; the
recommendation is to flood proof the homes.
The process in this reach is channel migration and potential flooding. It is not
clear whether the new Fairfield Drive Bridge alleviated flooding in this reach. A
pedestrian bridge and aerial sewer crossings at the upstream edge of Cardinal
Park (at the downstream end of this reach) are constricting the flow, which may
continue to cause flooding. Field observations indicate the new bridge and
sediment transport through the reach are aggravating the channel migration. To
lessen flooding, restore sediment transport competency and alleviate channel
migration in this reach, we recommend 319MS03 – Bankfull Floodplain
Downstream of Fairview Drive Culvert. This involves a two stage channel with
a bankfull floodplain along the left descending bank downstream of the culvert
11-4
and guide vanes along the toe of the right descending bank to reduce near bank
stress. The overbank or floodplain should extend downstream of the pedestrian
bridge and in-stream utilities to provide conveyance around these restrictions.
Fishpot Main Stem
FIS-18: Flooding of Two Homes in the Area of Mockingbird Park describes
the problem as flooding of two homes by the 100-year storm and recommends
flood proofing the homes. We concur with this recommendation and have
numbered it 319MS054– Flood Proof Homes.
The next downstream SSMIP intervention is FIS-17: Flooding of Eight Homes
Upstream of West Skyline Drive which describes the problem as one home
flooded by the two-year storm, three by the 15-year storm and four by the 100year storm. The recommended solution is to widen the channel by about 15 feet
for 1400 feet upstream of West Skyline Drive using three rows of vertical
gabions. This is estimated to increase the channel capacity by about 33%. FIS16: Overtopping of West Skyline Drive by 100-Year Storm is related to FIS-17
in that the inadequate West Skyline Drive culvert contributes to the upstream
flooding. FIS-16 describes the problem as inadequate capacity of the existing
structure (180 square foot opening). The recommendation is to increase capacity
by replacing the existing arch bridge structure with the equivalent of three 8-foot
by 12-foot parallel boxes. This provides a capacity increase of approximately
60%.
The process through this reach is vertically stable to depositional throughout with
lateral stability in the middle and lower part of the reach and meander migration
in the upper part of this reach. Based on the geomorphic analysis, the average
stream width at the base of the channel upstream of the West Skyline Culvert is
28 feet. We estimate bankfull width to be approximately 30 feet, as indicated by
a persistent lower limit of woody vegetation along the left descending bank at 2.5
feet above the channel bed. The existing channel slope is roughly 0.008
upstream of the existing West Skyline culvert. With this process in mind,
overwidening the low flow channel and installing vertical gabion is not a
sustainable solution. Additionally, there is no mention of incorporating a
functional channel shape in the new West Skyline Drive opening.
We recommend 319MS08 – Bankfull Floodplain and West Skyline Bridge
which entails replacing the existing West Skyline culvert with an 80ft span bridge
and constructing a stable, two-stage channel under the bridge and through the
upstream reach. The low flow channel here accommodates sediment transport
and stable fluvial process during and below dominant discharge flows while the
channel above bank full elevation will provide capacity during high flows without
causing damage upstream and downstream.
11-5
We stress that these two interventions, construction of the two-stage channel and
replacement of the culvert, are not separable. The constriction at the West
Skyline culvert must be removed. However, providing bankfull capacity without
preparing the channel upstream will induce erosion and may not address the
flooding. Conversely, providing the bankfull upstream without changing the West
Skyline constriction may also not address flooding.
Fishpot Main Stem
The next set of SSMIP interventions downstream of West Skyline Drive are FIS15: Flooding of Two Homes Upstream of Smith Drive, FIS-14: Overtopping
of Smith Drive by 100-Year Storm, and FIS-13: Flooding of Two Homes
Downstream of Smith Drive. The FIS- 15 problem involves homes on both
sides of the channel that are flooded by the 100-year storm. The recommended
alternative is to flood proof the homes. The FIS-14 problem is described as
inadequate capacity of existing structure (three 7-foot by 10-foot box culverts)
and the flooding of Smith Drive obstructing the intersection of Smith Drive and
Vlasis. This prevents access to 59 residences. The recommendation is to
increase capacity by about 25% by adding one 7-foot by 10-foot parallel box. The
FIS-13 problem describes two structures on the left (east) side of the channel
that are flooded by the 100-year storm. The recommendation is flood proofing the
homes.
Upstream of the Smith Drive culvert, the process is deposition accompanied by
widening with subsequent meander migration. Downstream of the Smith drive
culvert the channel is stable. There is a 1.5’ knick point immediately downstream
of the Smith Drive culvert. The additional barrel recommended in FIS-14 would
over widen the stream if added at the existing sill elevation and likely induce
upstream incision and eventual loss of culvert capacity. The additional capacity
under Smith Drive may alleviate the FIS-15 and FIS-13 flooding.
To alleviate property flooding upstream and downstream of Smith Drive and
overtopping of the Smith Drive culvert, we recommend 319MS09 –Smith Drive
Bridge which entails removing the existing Smith Drive triple box culvert and
replacing it with an 80ft span bridge. We also recommend incorporating the 1.5ft
knickpoint into the design to improve capacity and conveyance under the new
bridge. This can be accomplished by grade controlling upstream and
downstream of the bridge to turn the 1.5ft knickpoint into a knickzone between
the grade controls. The local increase in bed slope may allow a lower chord for
the new bridge. We recommend a two stage channel design that accommodates
the increase in slope between the two grade controls. Transition zones will also
be necessary upstream and downstream to insure the local slope increase does
not cause damage elsewhere in the system.
11-6
Fishpot Main Stem
The next group of SSMIP interventions are FIS-12: Flooding of Five Homes
and Businesses Upstream of Manchester Road, FIS-11: Overtopping of
Manchester Road by 2-Year Storm, and FIS-10: Flooding of 10 Businesses
on Left Bank Downstream of Manchester Road. In the FIS-12 problem
statement three businesses are flooded by the 2-year storm and two homes are
flooded by the 15-year storm. The recommendation is flood proofing the
structures. In FIS-11 the problem is described as inadequate capacity at the
existing Manchester Road culvert (two 8.5-feet by 14-foot RCP box culverts). The
recommended solution is to increase the capacity by 100% by adding two 8.5foot by 14-foot parallel RCP boxes. The FIS-10 problem is described as structure
flooding immediately downstream of Manchester Road by the 15-year storm; the
recommended alternative is to flood proof the structures.
The process upstream of Manchester Road is deposition with subsequent
widening with subsequent meander migration at the upstream end of the reach.
The mid and lower parts of the reach are stable in plan form. Downstream of
Manchester Road is a stable transport reach with bedrock control. Again, adding
capacity to the Manchester Road culvert by widening at the base will over widen
the channel and cause damage upstream and downstream.
We recommend 319MS10 - Manchester Road Bridge which entails replacing
the existing culvert with a 100ft span bridge to accommodate sediment transport
and large storm flows. Sediment transport and channel stability will be
accommodated with a two stage channel under the bridge. The new bridge and
channel design should include a hydraulic model of proposed conditions to
determine the effect of the new bridge on flooding upstream and downstream.
The existing recommendation of floodproofing property upstream and
downstream of the new bridge should only be included in this project if the redesigned channel and bridge do not satisfactorily reduce flood elevations.
The next two SSMIP interventions are FIS-09: Flooding of One Home and One
Church Upstream of Old Ballwin Road and FIS-08: Flooding of Two
Structures and Channel Erosion between Ramsey and Old Ballwin Road. In
FIS-09 the home and church are flooded by the 15-year storm. The
recommended alternative is to flood proof the structures. In FIS-08 one business
is flooded by the 15-year storm and one church is flooded by the 100-year storm
in addition to channel erosion for portions of the reach. The FIS-08
recommendation is also floodproofing the structures.
319MS12 – Floodproof structures at Old Ballwin Road recommends
floodproofing three structures and addresses all the FIS-09 structure flooding in
addition to the FIS-08 structure flooding at Old Ballwin Road. This is a stable
11-7
reach and the FIS-08 bank erosion is caused by overbank dumping of wood
chips, plant buckets, pallets, mulch and other material along 500 to 600feet of the
right descending bank immediately downstream of Old Ballwin Road. The bank
erosion is a self-inflicted problem caused by excessive overbank dumping and
therefore not a public improvement problem. We recommend that the local
business acquire a 404 or 401 permit and remove all the material that they’ve
dumped back to the original bank line. The stream bank should then be
stabilized with vegetative methods.
The remaining FIS-08 structure flooding at Ramsey Lane is addressed in
319MS14 described in the following reach summary.
Fishpot Main Stem
SSMIP recommendation FIS-07: Overtopping of Ramsey Lane by 15-Year
Storm indicates that the existing structure (three 8-foot by 12-foot box culverts)
capacity is inadequate and the capacity should be increased by 60% adding two
8-foot by 12-foot parallel RCP boxes.
A sanitary sewer crossing is restricting flow immediately downstream of Ramsey
Lane. The reach downstream and upstream is stable. Any recommendation to
alleviate flooding must also accommodate natural stream function. To reduce
flooding and overtopping of Ramsey Lane we recommend 319MS14 – Add
Bankfull Flow Capacity at Ramsey Lane which entails adding capacity to the
high flow channel with four 5ftX10ft barrels. The new barrels must be constructed
at the bankfull elevation which is about 3ft higher than the existing culvert sill. By
adding capacity to the overbank only, we do not over widen the stream which
would result in immediate stream instability and damage upstream and
downstream. The barrels should be split with three new barrels on the right
descending side and one new barrel on the left descending side.
As part of 319MS14 we also recommend removing the channel constriction at
the sewer line crossing downstream of Ramsey Lane. After removing the grouted
riprap on either side of the channel the banks should be stabilized by installing a
composite revetment.
11-8
FIS-06: Channel Erosion Upstream of Ries Road identifies nine lots on both
sides of the channel that have erosion and erosion potential as well as two
outbuildings at risk. The FIS-06 recommendation is to install approximately 600
linear feet of vertical gabions about 11 feet high on both sides of the channel.
This reach, along Essen Lane and Rethmeier Court, is in deposition and
widening or migrating. Coarse sediment deposition upstream of the Ries Road
culvert has triggered the channel widening and migration. The gabions and
subsequent overwidening would damage the upstream and downstream reach
and aggravate the current problem.
Therefore, we recommend 319MS15 – Weirs Upstream of Reis Road which
entails installing a series of upstream pointing weirs through the widening and
migrating reach. The weirs will to allow for sediment transport, while reducing
near-bank shear and stress along the bank toes. The last rock weir in the series
(closest to Reis Road) should double as a grade control. The rock structures
should be constructed low enough that they are hydraulically transparent during
high flows thereby causing no adverse effect on flood conveyance. We
recommend constructing this intervention in conjunction with 319MS16 – Reis
Road Bridge.
The SSMIP intervention FIS-05: Overtopping of Ries Road by the 100-Year
Storm describes the problem at Reis Road as inadequate capacity at the
existing culvert (four 8ft by 12ft box culvert) and recommends adding one 8ft by
12ft which increases the capacity by about 20%. The existing culvert is poorly
aligned and perched above the channel bed. These two factors not only
influence flood frequency, but also influence sediment transport and the
upstream deposition responsible for bank erosion. 319MS16 – Reis Road
Bridge recommends removing the existing four 8ftX12ft barrel culvert and
replacing it with a 100ft span bridge. The new bridge will include a two stage
channel to accommodate fluvial process and sediment transport through all
flows. Since the existing culvert is perched, the new channel under the bridge will
be lower than the existing culvert sill which will help with sediment transport.
Fishpot Main Stem
Reis Road to Lindy Road Reach
The SSMIP intervention FIS-04: Flooding of 25 Homes and Channel Erosion
Between Lindy Drive and Ries Road reports three homes flooded by the 2-year
storm, 12 by the 15-year storm and 10 by the 100-year storm. The recommended
option included widening of the channel by about 25 feet for the entire length
between Lindy Drive and Ries Road. This is estimated to increase the channel
capacity by about 50%. Channel lining includes vertical gabions five rows high
because of space and easement constraints.
The upper portion of this reach along Brookside Lane is generally stable in plan
and profile with minor local plan form migration limited by bedrock control. The
11-9
banks on the lower portion of this reach are concrete lined with a natural gravel
bed. Here again, gabion lining and widening the channel will create damaging
stream energy without sustainably solving the problem. We recommend rejecting
this option. Instead, we recommend 319MS17 – Bankfull Floodplain between
Reis and Lindy Roads which uses a combination of a bankfull floodplain and
locally raising the low points along the bank. This will mitigate property flooding
along this reach without damaging the upstream and downstream reaches.
Fishpot Main Stem
Lindy Road to Wren Avenue Reach
FIS-03: Flooding of 16 Homes and Channel Erosion Between Sulphur
Springs Road and Lindy Drive describes three homes flooded by the 2-year
storm, nine by the 15-year storm and four homes by the 100-year storm. The
recommended option included widening of the channel for the entire length
between Sulphur Springs Road and Lindy Drive (approximately 1,800 feet). This
is estimated to increase the channel capacity by about 50%. The FIS also
included lining the channel with vertical gabions four rows high because of space
and easement constraints.
The reach is a concrete prismatic channel. There is a 4ft drop in bed elevation
near the end of Jamboree Drive and an elevated 10in ductile iron pipe sewer line
with concrete wing walls constriction at the bottom of the reach. The reach
immediately downstream of Lindy Drive is depositional with center bars in the
channel bed. The stream achieves transport competency proceeding
downstream. The sewer line constriction most likely aggravates the deposition
through this reach. The reach downstream of the concrete channel is stable.
The active channel width in the natural channel downstream of the concrete
channel is 40ft to 44ft.
To accommodate sediment transport and natural stream function through the
dominant discharge and protect structures from flooding during storms, we
recommend 319MS19 – Bankfull Floodplain between Lindy Road and
Sulphur Springs Road which involves removing the concrete channel and
installing a two stage channel from Lindy Drive to Chappel Court and Woodland
Hill Court. This project should be done in combination with 319MS19 –
Replacement of Aerial Sewer Line at Chappel Court. The existing 4ft drop in bed
elevation can be incorporated into the final design to locally steepen the water
surface if needed to locally lower the water surface elevation during extreme
storms. Concept level analysis indicates that a 40ft wide bottom with a 20ft wide
bankfull elevated 3ft above the channel bed will accommodate dominant
discharge and flooding flows. The concept level analysis included 2H:1V side
slopes for the low flow channel and 3H:1V side slopes for the high flow channel.
11-10
Concrete and cobbles accumulated along an exposed sanitary sewer line
crossing near Chappel Court cause backwater and a local increase in water
elevation during high flow events.
Fishpot Main Stem
The next SSMIP intervention is FIS-02: Erosion of Sewer Utility Line at Big
Bend Woods where erosion is scouring a hole at a sewer line crossing Fishpot
Creek downstream of Big Bend Woods. There is also excessive shear in the
same vicinity because of poor alignment and flow approaching the roadway
culvert. The SSMIP solution is to dump riprap at the location to protect the sewer
and minimize future scour. This problem was addressed as part of the Fishpot
East Sanitary Sewer Relief Phase I design. The final design was a composite
revetment and boulder reinforced toe along the left descending bank immediately
downstream of the Big Bend Woods culvert. More detailed design
recommendations are presented in “Concept Plan for Big Bend Woods Drive”
prepared by Intuition & Logic.
Fishpot Main Stem
Hanna Road to Meramec River Confluence Reach
The next SSMIP intervention is FIS-01: Overtopping of Hanna Road by 2-Year
Storm. The recommendation is to raise the road approximately seven feet for
approximately 1000 feet. Most of the area to be raised is north of the bridge with
only a very small distance on the south side of the existing bridge. Raising the
road will increase the flood level upstream; however, the residences in this area
are high and do not appear to be in jeopardy. There are more than 500 homes
that need emergency access by either Hanna Road or Sulphur Springs Road
especially when the new levee at Valley Park is completed and the floodgates
are closed. Hanna Road is the main emergency access during flood events.
The reach immediately upstream of Hanna is depositional and stable in plan
form. However, the bridge is a sediment dam, which aggravates flooding. We
recommend 319MS29 – Hanna Road Bridge Improvement, raising Hanna
Road and building a new bridge with a two stage channel underneath. This
approach will accommodate sediment transport as well as extreme storm flows,
without causing an increase in upstream flood elevations.
The only SSMIP recommendation for Valley Park Tributary is FIS-23:
Overtopping of Crescent Road by 2-Year Storm. According to the SSMIP, the
existing Crescent Road culvert (4-foot by 6-foot box culvert) has inadequate
capacity. The recommendation is that the capacity should be increased by
11-11
replacing the existing culvert with the equivalent of one 8-foot by 12-foot RCP
box. This would increase the capacity of the crossing by about 300%.
We recommend 319VP1 – Crescent Road Two Stage Culvert. Since the
existing culvert capacity is inadequate, we recommend replacing the culvert with
a twin barrel, two stage culvert. A single 8-foot by 12-foot culvert would only over
widen the low flow channel and immediately begin to fill in as the stream reestablishes a functional section shape. Instead, the two stage culvert has one
barrel to accommodate low flow, while the other barrel would be installed at
bankfull elevation to accommodate high flows.
The first SSMIP intervention on Holly Green Tributary is FIS-25: Overtopping of
Oak Street by 100-Year Storm. According to the SSMIP, capacity at the
existing structure (two 8-foot by 10-foot RCP box culverts) is inadequate. The
recommended solution is to increase capacity by about 40% by adding a single
8-foot by 10-foot parallel RCP box.
We recommend 319HG3 – Flood Reduction at Big Bend Road. Immediately
upstream of the Big Bend Road (Oak Street) culvert, the Holly Green Tributary is
depositional and laterally stable. The box culvert at Big Bend Road is presently
acting as a de facto grade control. The accumulation of bed material and debris
has induced overtopping of Big Bend Road by the 100-year flood. Removing the
culvert or constructing an additional 8-foot by 10-foot culvert opening would
propagate channel incision and could initiate an unraveling of what is now a
vertically stable reach upstream of the existing culvert. We recommend putting a
nose on the center pier, or wall, of the existing double box culvert. In addition,
flanking culverts could be added on either side, elevated about 4 feet from the
existing culvert flowline, to improve conveyance during bankfull flow without
changing hydraulic grade during low-flow conditions.
The next SSMIP intervention along the Holly Green Tributary is FIS-24:
Overtopping of Sulphur Springs Road by 100-Year Storm. According to the
SSMIP, the existing roadway overtops by 12 inches. The proposed solution is
raising the roadway by about 2 feet, for a total distance of approximately 2,000
feet roughly evenly distributed on both sides of the bridge.
This problem has already been addressed by the replacement of the old roadway
with two new 15-foot by 10-foot box culverts.
FIS-28: Erosion of Bank at 504 Vernal Hill Court identifies erosion threatening
a single structure and appurtenances. The recommended solution includes two
gabions two rows high for a distance of 100 linear feet. FIS-27: Erosion of
11-12
Bank at 531 Briar Hill, 567 and 568 Vernal Court also identifies erosion
potentially threatening a habitable structure and appurtenances. This solution
includes the placing gabions four rows high on the left bank for a distance of 60
feet.
In response to both FIS-28 and FIS-27, we recommend 319NB5 – Grade
Stabilization and Rock Toe at Vernal Hill and Briar Hall Courts. Channel
incision, the dominant fluvial process along this reach, has resulted in bank
failures that have exposed a sanitary manhole on the left descending bank and
the sanitary line crossing in the channel bed behind Briar Hall Court. The
channel is widening downstream of the sanitary line. We recommend a grade
control at the exposed sanitary sewer line, to protect the sewer line and maintain
channel grade, with a rock toe to protect both banks upstream and downstream
of the grade control.
The next SSMIP proposed intervention is FIS-26: Overtopping of Ries Road by
15-Year Storm. According to the SSMIP, the existing roadway overtops by
about 2 feet. This solution is to raise the roadway by about 3 feet for a distance
of approximately 250 feet. The length to be raised was on the north side of the
culvert. In addition, the FIS recommended replacement of the existing culvert
with an 8-foot by 12-foot RCP box culvert.
This recommendation has been implemented although the single box culvert was
replaced by twin boxes. The altered channel began losing capacity as soon as it
was built. The left descending box of the Reis Road culvert has lost nearly onequarter of its flood capacity due to deposition. We recommend 319NB8 – Bank
Stabilization at Reis Road. New Ballwin Tributary is depositional, and laterally
adjusting by means of meander migration at Reis Road. The box culvert at Reis
Road should be re-shaped to improve the approach to the culvert. We
recommend improving the approach and constructing a weir to guide the flow
into one of the boxes, but that flushes out the other box under high flows. We
recommend rock toe protection and urban forestry immediately downstream of
Reis Road to counter the loss of riparian vegetation at the top of the bank and to
prevent gradual bank erosion.
Larkhill Tributary
The SSMIP has identified one problem site along the Larkhill Tributary, FIS-29:
Flooding of 33 Homes in Winchester between Hillcrest and Roland.
According to the SSMIP, the existing storm sewer (48-inch RCP) running through
Winchester (from Ballwin on the north to the Creek on the south) has inadequate
capacity. Excess flow and debris on the upstream side cause overland flow
through Winchester, which potentially affects the 33 homes in the flow path.
Upstream storage is the recommended solution. This option included creation of
a 2-acre pond with capacity to provide 5 feet of live storage or (10-acre-feet). An
outlet structure sized so as to limit discharges to the capacity of the downstream
11-13
48-inch sewer will also be provided. This site is in a developing commercial area
so has some potential business use. Although this is the least expensive and
preferred solution, timing and development pressure may make the window of
opportunity rather short. We concur with the existing SSMIP recommendation.
Table 11.0 presents the SSMIP recommended projects and the corresponding
319 recommended projects. The 319 management recommendations based on
geomorphologic data as well as the hydraulic model had a capitol cost of $14.2
million which is a $3.6 million cost reduction over the $17.8 million SSMIP. We
acknowledge that there are five SSMIP projects (FIS-02, 20, 21, 24, and 26) that
were built prior to this report and consequently there are no 319 cost estimates
associated with these structures. The SSMIP estimate for these projects totaled
$2.2 million. However, we estimate the cost of ameliorating the unintended
damage associated with the installation of these structures at $1.0 million. This is
the total opinion of cost for 319 projects 319MS01, 319MS02, 319MS03 and
319NB09.
11-14
Table 11.0 SSMIP and corresponding 319 Projects
SSMIP
Project
Number
SSMIP Problem Description
FIS-01
Overtopping of Hanna Road by 2- year
storm.
FIS-02
Sewer line exposed at scour hole
SSMIP Proposed Solution
Raise 1000 linear feet of roadway.
SSMIP Cost 319 Project Description
$
Dump rip-rap to protect the sewer line. $
FIS-03
Frequent flooding 3 homes by the 2-yr storm, Widen approximately 1800 linear feet
9 by the 15-yr storm, and infrequent flooding of channel and install vertical gabions
of 4 by the 100-yr storm
on both banks.
FIS-04
Frequent flooding 3 homes by the 2-yr storm, Widen the channel and install vertical
12 by the 15-yr storm, and infrequent flooding gabion baskets on both sides of the
of 10 by the 100-yr storm
channel.
319MS29 – Hanna Road Bridge
1,244,000 Improvement
Total
$
Problem addressed in East
11,000 Sanitary Relief Phase I
2,332,800
N/A
$
319MS19 – Bankfull Floodplain
between Lindy Drive and
2,485,000 Sulphur Springs Road
$
1,517,300
$
between Reis Road and Lindy
5,742,000 Drive
$
2,612,600
FIS-05
Infrequent flooding of Reis Road by the
100-yr storm
Add a parallel 8x10 RCP box culvert.
$
100,000 319MS16 – Reis Road Bridge
$
1,187,200
FIS-06
Nine lots with 2 outbuildings have erosion
and erosion potential on both sides of the
channel
Install approximately 600 linear feet of
vertical gabions about 11 feet high on
both sides of the channel.
$
319MS15 – Weirs Upstream of
754,000 Reis Road
$
285,000
$
319MS14 – Add Bankfull Flow
282,000 Capacity at Ramsey Lane
$
569,500
Floodproofing homes and installing
approximately 600 linear feet of
gabions about 12 feet high on the right
$
bank.
319MS14 – Add Bankfull Flow
420,000 Capacity at Ramsey Lane
FIS-07
Frequent overtopping of Ramsey Lane by the Add a parallel 8x10 RCP box culvert
15-yr storm
under the road.
FIS-08
Frequent flooding of one business by the
15-yr storm and infrequent flooding of one
church by the 100-yr storm
FIS-09
Frequent flooding of one home and one
church by the 15-yr storm
Floodproofing
$
FIS-10
Frequent flooding of 9 businesses in a strip
mall and 1 stand alone business on the left
bank of the channel by the 15-yr flood
Floodproofing
$
319MS10 - Manchester Road
125,000 Bridge
FIS-11
Frequent overtopping of Manchester Road by
the 2-yr storm
Install 2 parallel 8x10 RCP box
culverts.
$
1,000,000 Bridge
11-15
319MS12 – Floodproof
83,000 Structures at Old Ballwin Road
Duplicate
$
125,000
$
1,866,900
Duplicate
SSMIP
Project
Number
FIS-12
Frequent flooding of 3 businesses by the 2-yr
storm and 2 homes by the 15-yr storm
Floodproofing
$
FIS-13
Infrequent flooding of 2 homes on the left
bank by the 100-yr storm.
Floodproofing
$
83,000 319MS09 – Smith Drive Bridge
FIS-14
Infrequent overtopping of Smith Drive by the
100-yr storm.
Install a parallel 7x10 RCP box culvert. $
Duplicate
FIS-15
Infrequent flooding of 2 homes, 1 located on
each bank of the channel, by the 100-yr
storm
Floodproofing
$
Duplicate
FIS-16
Infrequent overtopping of West Skyline Drive
by the 100-yr storm.
Replace the existing 180 square foot
bridge opening with 3 8x12 RCP box
culverts.
$
421,000 and West Skyline Bridge
FIS-17
Frequent flooding of 1 home by the 2-yr
storm, 3 by the 15-yr storm and infrequent
flooding of 4 homes by the 100-yr storm.
Homes are located on both banks of the
channel.
Widen channel and install vertical
gabions about 9 feet high for
approximately 1400 linear feet on both
sides of the channel.
$
1,624,000 and West Skyline Bridge
FIS-18
Infrequent flooding of 2 homes on the left
side of the channel by the 100-yr storm.
Floodproofing
$
83,000 319MS05 – Flood Proof Homes
$
83,000
FIS-19
Frequent flooding of 2 homes by the 2-yr
storm and 1 home by the 15-yr storm on the
left bank of the channel.
Floodproofing
$
Downstream of Fairview Drive
125,000 Bridge
$
398,000
FIS-20
Frequent overtopping of Fairview Drive by
the 15-yr storm.
Replace the existing 156 square foot
opening with 3 parallel 8x12 RCP box
culverts.
$
FIS-21
Frequent flooding of 2 homes by the 2-yr
storm.
Floodproofing.
$
11-16
Total
146,000 Bridge
Problem addressed by
Fairview Drive Bridge
411,000 Replacement
Problem addressed by
Fairview Drive Bridge
83,000 Replacement
Duplicate
$
$
788,600
1,229,500
Duplicate
N/A
N/A
SSMIP
Project
Number
FIS-22
Erosion adjacent to Field Avenue is
threatening the roadway.
the left side of the channel.
$
FIS-23
Frequent overtopping of Crescent Road by
the 2-yr storm.
Replace the existing 4x6 RCP box
culvert with a 8X12 RCP box culvert.
$
FIS-24
Infrequent overtopping of Sulphur Springs
Road by the 100-yr storm.
FIS-25
Infrequent overtopping of Oak Street (Big
Bend) by the 100-yr storm.
Add a parallel 8x10 RCP box culvert.
$
319HG5 – Big Bend Road
148,000 Culvert
FIS-26
Frequent overtopping of Reis Road by the
15-yr storm.
Raise 250 linear feet of road an
average of 3 feet and replace the
existing 6x8 RCP box culvert with an
8x12 RCP box culvert
$
Problem addressed by Reis
302,000 Road Culvert Replacement
FIS-27
Bank erosion potentially threatening 1
structure.
the left side of the channel.
FIS-28
Bank erosion threatening structures.
FIS-29
Frequent flooding of up to 33 homes in
Winchester by overland flow.
Raise approximately 2000 linear feet of
$
road about two feet average
$
Install approximately 100 feet of
$
the right side of the channel.
Construct an upstream detention pond
to reduce flows reaching the culvert
$
through Winchester.
319MS01 – Guide Vanes at
30,000 Field Avenue
319VP1 – Crescent Road Two
77,000 Stage Culvert
Problem addressed by Sulphur
Springs Road Culvert
1,425,000 Replacement
$
85,400
$
258,500
N/A
$
265,900
N/A
319NB07 – Grade Control
Exposed Sewer and Rock Toe
43,000 High Bank at Briarhill Court
$
114,100
319NB05 – Rock Toe at 504
43,000 Vernal Hill Court
$
95,700
319LH1 – Winchester Detention
362,000 Pond
$
362,000
SSMIP TOTAL = $ 17,818,000
11-17
Total
319 TOTAL =
$ 14,177,000
12.0 CONCLUSIONS AND IMPLICATIONS FOR FUTURE MANAGEMENT
The comparison of the approaches to stormwater management in the SSMIP and
those presented here provides useful insight. Certainly, the watershed-scale
hydrologic and hydraulic models in the SSMIP represent a major advance over
previous methods by quantifying one of the main driving forces in urban stream
dynamics - water. But as this analysis illustrates, hydrologic and hydraulic
models alone are an insufficient basis for watershed management decisions.
Effective stream management must include analysis of water and sediment as
the driving forces, channel shape, material and strength as the resisting forces
and evaluation of the stream response to change. We conclude that sediment
eroded from the headwaters and inadequate sediment transport through the mid
and lower reaches are the dominant fluvial processes in the Fishpot Creek
Watershed. Sediment drives the behavior of this stream; its transport and
deposition must be reflected in any successful management plan. Further, all
interventions in this system must accommodate the reach specific process to
solve the identified problems and prevent the creation of new problems through a
predictable stream response.
Most of the recommended SSMIP interventions do not accommodate the
dominant process nor do they consider the stream’s response to the intervention.
This is a major flaw in any plan intended to address flooding or erosion.
Moreover, the SSMIP process can not identify serious instabilities in both the
headwaters and lower Fishpot Creek.
With the exception of a handful of floodproofing recommendations, most flooding
problems are addressed by enlarging the channel without regard for whether the
recommended channel dimensions are stable. In the eight major
recommendations concerning bank erosion, armor in the form of vertical gabion
walls were recommended without determination of whether active erosion was
actually occurring or consideration to the upstream and downstream effects. The
emphasis on landowner-diagnosed complaints and the absence of information
about stream response has lead to failures of the installed treatments and
damage to adjacent reaches as a result of these treatments. If the SSMIP is
implemented, more failed treatments and proliferation of stream problems are
inevitable. We recommend the current SSMIP list of proposed projects be
abandoned and replaced with those interventions identified in this report.
The advocates of the SSMIP approach argued throughout this project that the
isolated repairs represented the only cost effective way to address the region’s
ever-growing stormwater needs. Systemic management of the stream was
presumed to be far too expensive. This proved not to be the case. While the
management recommendations generated by the geomorphologic analysis were
systemic in nature, we were able to attribute specific measures to the previously
identified list of complaints. The management recommendations based on
12-1
geomorphologic data as well as the hydraulic model had a capitol cost of $14.2
million which is a $3.6 million cost reduction over the $17.8 million SSMIP.
However, any reasonable evaluation of relative costs must consider the tendency
for SSMIP treatments to either fail or propagate the problem elsewhere
potentially giving rise to a new series of complaints.
Fluvial geomorphology allows diagnosis of the cause of stream problems and
informs management approaches that work with, rather than against, stream
process. This allows the designer to meet the requirements of affected citizens
by working in a systemic context. This is a step change in the evolution of
stormwater management and, like all major changes, poses real challenges.
Most local stormwater engineers and agency staff are not trained in stream
mechanics or in sedimentology. Consequently, there are still strong voices
arguing that hydraulic models provide all the information necessary for effective
storm water management. We also acknowledge that citizens quickly become
impatient with any activity that smacks of academic study and place intense
political pressure on agencies to stop studying and fix their complaints. However,
implementing designs based on partial information by excluding fundamental
stream mechanics from the analysis will not solve the problem and will likely lead
to yet another round of complaints.
Despite these considerable barriers, it appears that acceptance of fluvial
geomorphology and its role in stormwater management is increasing. While
some citizens still look upon all streams as storm sewers, a growing number
regard their streams as assets and demand that they be managed in less
destructive ways. In addition, some municipal engineers have concluded that the
isolated repairs advocated in the SSMIP are ineffective and are searching for an
alternative. At least two cities in the St. Louis area have completed
geomorphologic analyses of the watersheds in their jurisdictions and have
sharply modified their own stream treatments in light of those findings.
In Fishpot Creek, the District has built a series of sanitary line crossings based
on stream mechanics principles. The crossing structures are designed to
dissipate energy at desired points and in some cases to guide flow around
bends. This is an improvement over previous practices in which sanitary lines
often crossed streams at oblique angles focusing flow against one of the banks
and causing a recurring erosion problem.
The implications of this project on stormwater management in our region are
important. Through this grant process, we have presented compelling evidence
that a more systematic approach to stormwater management offers functional,
financial and ecological advantages over the present system. It is reasonable to
suggest that the results of the comparison offered here are not unique and that
parallel evaluations of the remaining SSMIPs would yield similar results.
12-2
13.0 BIBLIOGRAPHY
Bagnold, R.A., 1960. Some Aspects of the Shape of River Meanders, Geological
Survey Professional Paper 282-E, US Government Printing Office, Washington.
Benham, K.E. 1982. Soil survey of St. Louis County and St. Louis City,
Missouri. US Department of Agriculture Soil Conservation Service (NRCS).
Bohn H., B. McNeal and G. O’Conner, 1985, Soil Chemistry, 2nd Ed., John Wiley
& Sons.
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Center for Watershed Protection, 2000, Model Development Principles for
Central Rappahannock, VA. Ellicott City, Maryland.
Chang, H.H., 1998. Fluvial Processes in River Engineering, Frieger Publishing
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Banks of Some Common Riparian Species: Are Willows as Good as it Gets?,
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Effects of Riparian Vegetation on River Bank Stability, Proceedings ASCE
Environment and Water Resource Institute, Reno, NV.
Derrick, D., 2002. Stream Investigation, Stabilization and Design Workshop,
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Ferguson, B.K., 1994. Stormwater Infiltration, Lewis Publishers.
Franzius, O., 1936. Waterway Engineering, Technology Press, Massachusetts
Institute of Technology.
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13-1
Gray, D.H. and H. Ohashi, 1983. Mechanics of Fiber Reinforcement in Sand, J.
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Phenomena, Scientific American, W.H. Freeman and Co. San Francisco,
California
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Geomorphology, W. H. Freeman and Co. Dover, New York.
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Springer-Verlag.
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Morphology, Dynamics and Control, Water Resources Publications.
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Earth Surface Processes and Landforms, Vol. 14.
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New York.
13-2
Thorne, C.R., M.D. Newson and R.D. Hey, 1997. Application of Applied Fluvial
Geomorphology: Problems and Potential, Applied Fluvial Geomorphology for
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Reservoirs, US Army Corps of Engineers Engineer Manual EM 1110-2-4000.
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Projects, ERDC/CHL TR-01-28.
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13-3

Fishpot Creek Watershed - East

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