Pawtuxet River Restoration Project Pawtuxet River

Transcription

Pawtuxet River Restoration Project
Pawtuxet River, Cranston and Warwick, Rhode Island
Application to Alter
Prepared for
Pawtuxet River Authority
618 Main Street
Coventry, Rhode Island 02816
In conjunction with
Narragansett Bay Estuary Program
URI Bay Campus Box 27
Narragansett, Rhode Island 02882
Prepared by
EA Engineering, Science, and Technology, Inc.
2350 Post Road
Warwick, Rhode Island 02886
June 2010
FINAL
EA Project No. 62277.01
EA Project No.: 62277.01
Table of Contents
Page 1 of 3
June 2010
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
Page
1. PROJECT DESCRIPTION.................................................................................................. 1
1.1
Existing Conditions..................................................................................................... 4
1.1.1
1.1.2
1.1.3
1.1.4
1.1.5
1.1.6
1.1.7
1.1.8
General Environment .................................................................................... 4
Site History .................................................................................................... 5
Dam Structure and Hydraulic Function......................................................... 7
Geology and Soils ......................................................................................... 8
Wetland Resources ........................................................................................ 9
Fisheries......................................................................................................... 9
Infrastructure ................................................................................................. 10
Sediment ........................................................................................................ 11
1.1.8.1
1.1.8.2
1.2
Sediment Mobility .......................................................................... 11
Sediment Exposure ......................................................................... 11
Methodology ............................................................................................................... 12
1.2.1
1.2.2
Existing Data Review and Team Qualifications ........................................... 13
Field Effort .................................................................................................... 14
1.2.2.1 River Elevation Data ...................................................................... 14
1.2.2.2 Sediment Sampling......................................................................... 15
1.2.2.3 Wetland Assessment and Identification ......................................... 15
1.2.3
1.2.4
1.2.5
1.3
Hydrology and Hydraulic Analysis ............................................................... 16
Sediment Mobility Analysis .......................................................................... 18
Sediment Exposure Analysis ......................................................................... 20
Results ......................................................................................................................... 21
1.3.1
1.3.2
Existing Data Review .................................................................................... 21
Field Effort .................................................................................................... 24
1.3.2.1 River Elevation Data ...................................................................... 24
1.3.2.2 Sediment Sampling......................................................................... 25
1.3.2.3 Wetland Assessment and Identification ......................................... 27
1.3.3
1.3.4
1.3.5
Hydrology and Hydraulic Analysis ............................................................... 29
Sediment Mobility Analysis .......................................................................... 32
Sediment Exposure Analysis ......................................................................... 33
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Lower Pawtuxet River Restoration Project
Pawtuxet Falls Dam – Warwick, Rhode Island
Table of Contents
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Page
1.4
Description of the Proposed Action ............................................................................ 35
2. AVOIDANCE AND MITIGATION ................................................................................... 39
2.1
State-Regulated Resource Areas ................................................................................. 39
2.1.1
2.1.2
2.1.3
2.2
Freshwater Wetlands ..................................................................................... 39
Floodplain ...................................................................................................... 40
Office of Waste Management Regulations ................................................... 40
Infrastructure ............................................................................................................... 40
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
Infrastructure Scour Analysis ........................................................................ 40
Broad Street Bridge ....................................................................................... 41
Pawtuxet Dam Abutment Walls .................................................................... 41
Rhodes on the Pawtuxet ................................................................................ 41
Warwick Avenue Bridge ............................................................................... 42
Elmwood Avenue Bridge .............................................................................. 42
Other Structures ............................................................................................. 42
2.3 Historic and Cultural ................................................................................................... 42
2.4. Mitigation Measures ................................................................................................... 43
2.4.1
2.4.2
2.4.3
Impact Avoidance.......................................................................................... 43
Impact Minimization ..................................................................................... 45
Additional Review Criteria for Application to Alter..................................... 46
3. EVALUATION OF FUNCTIONS, VALUES, AND IMPACTS ....................................... 53
3.1
Impacts ........................................................................................................................ 53
3.1.1
3.1.2
3.1.3
3.1.4
Dam Structure and Hydraulic Function......................................................... 53
Geology and Soils ......................................................................................... 53
Wetland Resources ........................................................................................ 53
Wetland Functions, Values, and Impacts ...................................................... 55
3.1.4.1
3.1.4.2
3.1.4.3
3.1.4.4
3.1.4.5
3.2
Wetland and Wildlife Habitat......................................................... 56
Recreation and Aesthetics .............................................................. 58
Flood Protection ............................................................................. 59
Groundwater and Surface Water Supplies ..................................... 59
Water Quality ................................................................................. 60
Soil Erosion and Sediment Control............................................................................. 61
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Table of Contents
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Page
3.3
Alternatives to the Proposed Action ........................................................................... 61
3.3.1
3.3.2
3.3.3
3.3.4
Full Dam Removal Alternative ..................................................................... 61
Placement of a Rock Ramp ........................................................................... 62
Construction of a Denil Fish Ladder ............................................................. 62
No Action Alternative .................................................................................. 63
REFERENCES
FIGURES
APPENDICES
APPENDIX A: ARRA FUNDING DESCRIPTION
APPENDIX B: SUPPLEMENTAL REPORTS
APPENDIX C: DEED EVALUATION AND ABUTTER INFORMATION
APPENDIX D: JANUARY 29, 2009 PERMITTING STRATEGY MEMORANDUM
APPENDIX E: FIELD FORMS
APPENDIX F: HEC-RAS MODEL
APPENDIX G: SHEAR STRESS DATA
APPENDIX H: SEDIMENT SAMPLING AND GRAIN-SIZE ANALYSES RESULTS
APPENDIX I: PUBLIC ACCESS SURVEY
APPENDIX J: ENGINEERING DRAWINGS
APPENDIX K: NRCS DESIGN STANDARDS
APPENDIX L: RHODES ON THE PAWTUXET LETTER OF AUTHORIZATION
APPENDIX M: SHPO MOA
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List of Figures
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LIST OF FIGURES
Number
Title
1
Site Locus
2
Impact Areas
3
RIGIS Wetlands
4
Infrastructure
5
Ciba Geigy
6
USACE Dredging, Pawtuxet Cove
7
Transect and Sampling Locations
8
Analytical Sediment Sampling Locations
9
Potential Public Use Areas
10
Exposure Areas 4 – 10
11
Exposure Areas 18 – 22
12
FEMA Flood Zones
13
Cross Sections
14
Cross Sections
15
Cross Sections
16
Cross Sections
17
Restoration Construction Area Water Level Changes
18
Long-Term Restoration Area Water Level Changes
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List of Tables
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LIST OF TABLES
Number
Title
1-1
Fish Species Found in the Pawtuxet River
1-2
Discharge and Storm Recurrence at Pawtuxet Falls Dam
1-3
Fish Passage Hydraulic Requirements
1-4
2002 Ciba Sediment Sampling Results
1-5
River Bottom Elevations
1-6
Sediment Grain Size Results
1-7
Chemical Analysis Results
1-8
Existing and Proposed Water Elevations, NGVD 29 (Mean August)
1-9
Proposed Depths and Velocities after Partial Dam Removal
1-10
Representative Increases in Width of Riverbank Exposure Areas
3-1
Wetland Impacts
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1. PROJECT DESCRIPTION
The Pawtuxet River and its tributaries have been subjected to extensive physical modification to
accommodate human uses, including industrial power, transportation infrastructure, urbanization,
commercial development, water supply, flood control, and water treatment. These modifications
have substantially harmed the native ecology of the Lower Pawtuxet River (LPR), along with the
natural functions and values of its remaining wetlands. For purposes of this project, we define
LPR as the lower seven miles of the Pawtuxet River, from Pontiac Mills to Pawtuxet Cove on the
western shore of Narragansett Bay.
The purpose of the Lower Pawtuxet River Restoration Project (LPRRP) is to begin restoring the
native riverine ecology, fish populations, and wetlands functions and values of the LPR by
removing one of the most significant and harmful anthropogenic modifications to the physical
system: the Pawtuxet Falls Dam (PFD) in Warwick and Cranston, RI (Figure 1). Through this
action, the project proponent, Pawtuxet River Authority (PRA), and its federal, state, and nongovernmental partners – including the Rhode Island Department of Environmental Management
(RIDEM)–will:
1) Restore native riverine ecology by physically, and thereby biologically, reconnecting
the LPR with Narragansett Bay and coastal ecosystems. By restoring connectivity
between the watershed and estuary, the project will restore spawning habitat for
migratory fish such as river herring and American shad. These species are native to the
Pawtuxet River watershed and the restoration of spawning populations will have
significant benefits to fish and wildlife in the Pawtuxet River and its tributaries, as well as
Narragansett Bay. The LPR is listed by RIDEM as “Not Supporting” the use or
attainment of “Fish and Wildlife Habitat” in its 2008 Integrated Water Quality
Monitoring and Assessment Report, Section 305(B) State of the State’s Waters Report
and Section 303(D) List of Impaired Waters. The LPRRP is the single most significant
action that can be undertaken to improve fish and wildlife habitat on the LPR, thereby
directly supporting RIDEM’s water quality objectives and furthering attainment of this
designated use.
2) Restore native wetland functions and values to significant wetland complexes on both
sides of the LPR. Riverine wetlands serve as natural wildlife corridors for aquatic and
terrestrial species. By restoring natural flooding regimes and wildlife connectivity, as
well as native fish populations, wetlands of the LPR will be able to provide better natural
functions and values, such as wildlife habitat and flood storage. Piscivorous birds
(osprey, herons, egrets, mergansers) will greatly benefit from the restoration of migratory
fish populations, as will many wetland mammals (otters, mink, raccoons). The LPRRP is
part of an overall effort to improve the LPR, which includes the LPR Oxbows Floodplain
Restoration Project (OFRP), a new project initiated by the City of Cranston and USDA –
Natural Resources Conservation Service (NRCS) to preserve and restore floodplain
wetlands in the Fay Field area.
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3) Improve water quality in the LPR. Dams impair water quality by reducing velocity
and raising water temperature, which in turn increases stratification, reduces dissolved
oxygen levels, promotes bacterial growth, and promotes growth of algae, invasives, and
other aquatic nuisance plants. The LPRRP will improve water quality in the LPR and
nearby areas of Narragansett Bay by restoring natural stream velocity and temperature.
There are large amounts of nuisance algae in the LPR during the summer and the LPRRP
will address this problem by decreasing water temperature and residence time while
increasing stream velocity.
4) Reduce property flooding impacts. By restoring the river’s natural water surface
elevation (WSE) upstream of the PFD, the project is expected to reduce property flooding
of low-lying areas along the LPR, such as Rhodes on the Pawtuxet, and industrial and
residential areas along the river. The LPRRP is strongly supported by these property
owners.
The LPRRP has been identified as a high priority project by Governor Carcieri (E.O. 03-16) and
by RIDEM in its Strategic Plan for the Restoration of Anadromous Fishes to Rhode Island
Coastal Streams.
The LPRRP is led by the PRA with extensive technical and funding support and oversight
provided by the following agencies and organizations:
Federal
 USDA – Natural Resources Conservation Service
 National Oceanic and Atmospheric Administration
 U.S. Fish and Wildlife Service
 U.S. Environmental Protection Agency
State


R.I. Department of Environmental Management
R.I. Coastal Resources Management Council
Non-Governmental
 Pawtuxet River Authority (Project leader and Applicant)
 Narragansett Bay Estuary Program (Project manager and outreach)
 Save The Bay
 American Rivers
Engineering Consultants
 Kleinschmidt Associates (Kleinschmidt)
 Milone & MacBroom, Inc. (MMI)
 EA Engineering, Science, and Technology, Inc.
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Each of these agencies and organizations has extensive experience in river and wetland
restoration—in many cases, throughout the U.S. The LPRRP was developed through intensive
investigations and consultations with all of these experts and is strongly supported by them as
beneficial to the water quality, wetlands, fish, and wildlife of the LPR and Narragansett Bay.
Together, the federal, state, and non-governmental partners serve as the project management
team (PMT).
In designing the restoration project, the PMT interacted extensively with stakeholders and the
community through three major public meetings in Pawtuxet Village as well as many meetings
with business owners, municipal officials, elected officials, neighborhood organizations, and
private citizens in the community. The PMT has also engaged in several preliminary
consultations with the RIDEM Office of Water Resources and Office of Waste Management to
share the goals of the project and incorporate agency concerns. In addition, two major technical
studies and several smaller investigations were commissioned by the PMT. These studies are
detailed below and appended to this package in electronic format.
The LPRRP is funded through a variety of sources, including American Recovery and
Reinvestment Act (ARRA) funding through NRCS, and Narragansett Bay Watershed
Restoration Bond funding through RIDEM. A description of the ARRA funding associated with
this project is presented in Appendix A.
The focus of the LPRRP construction activity is the PFD, which is a concrete structure built in
1924 and located immediately upstream of the Broad Street Bridge in Pawtuxet Village,
Warwick and Cranston, RI (Figure 1). The PFD is approximately 170 feet long and connects
existing natural bedrock outcroppings, with an average structural height of approximately five
feet. The PFD affects approximately seven river miles along the main stem of the LPR as well
as approximately three river miles along the lower Pocasset River, and several lesser tributaries
by creating a barrier to fish and wildlife passage, as well as altering the natural flow regime,
natural flood stages, and natural seasonal WSEs along the LPR and associated wetlands. The
dam exacerbates property flooding under some flow conditions by increasing WSE upstream of
the PFD.
To rectify these impacts and restore native riverine ecology, the LPRRP proposes to remove a
150-ft portion of the PFD. Partial removal compensates for the out-of-basin transfer from the
Scituate Reservoir (estimated at more than 30 million gallons per day on average), restoring
parameters such as water depth and velocity at the mouth of the river comparable to those which
likely existed before development of the reservoir in 1925.
As noted above, this alternative was designed through two major technical studies, each of which
surveyed existing conditions and evaluated potential restoration alternatives using Hydrologic
Engineering Centers River Analysis System (HEC-RAS) modeling to predict expected changes
to WSE, velocity, sediment exposure, and sediment transport under various potential
alternatives. These studies were undertaken by Kleinschmidt Associates (2005) and Milone &
MacBroom (2008) and are included in Appendix B. Supplemental studies include detailed
wetland investigations and a study of historic resources, also included in Appendix B. More
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extensive topographic/bathymetric surveys were carried out at the request of RIDEM, and are
incorporated into the analysis herein.
For purposes of this application, the LPRRP is separated into two geographic areas: the LongTerm Restoration Area (LTRA), which is the entire area affected by the restoration; and the
Restoration Construction Area (RCA), a much smaller area affected by the actual dam removal
construction activity (Figure 2). This application analyzes and describes the affect of the LPRRP
on each of these areas.
Specifically, this application demonstrates that the project will have no negative impacts upon
issues relating to:
 Human health
 Wetlands
 Sediment transport
 Infrastructure
Moreover, the application demonstrates that the LPRRP will have a positive impact on the
ecology of the LPR, will restore wetland functions and values, will improve water quality, and
will enhance many associated environmental values, such as flood control and recreation.
The LPRRP represents an enormous commitment by federal, state, and non-governmental
environmental agencies, with the sole purpose of improving the environment of Rhode Island.
The PMT believes this to be one of the most significant environmental restoration opportunities
in Rhode Island and looks forward to continuing to work with RIDEM to complete this vitally
important project.
1.1
Existing Conditions
Information and data contained within this Application to Alter represents conditions within the
Pawtuxet River that existed prior to the historic flooding event of March/April 2010. This
flooding event represents a flood between the 100-year and 500-year frequency event, and as
such, conditions relating to bathymetry, sediment quality, wetland functions and values, and
other riverine conditions may no longer be identical to those represented by the data contained
within this Application. Given the dynamic nature of riverine systems, a discrepancy between
conditions observed during data collection activities and those as they currently exist is a likely
occurrence, especially as the age of the collected data increases. Therefore, the applicant
requests that the data contained within this application be considered accurate since riverine
conditions are never static and any updates to the data contained within the Application has the
ability to change due to forthcoming flood events.
1.1.1
General Environment
The Pawtuxet River is the third largest tributary of Narragansett Bay and its watershed is the
largest sub-basin of Narragansett Bay located entirely within the state of Rhode Island. Like all
northeastern river system of comparable size, the Pawtuxet River is a dynamic environment,
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particularly in its lower reaches. Under existing conditions, the WSE of LRP fluctuates
seasonally and as a result of episodic flooding events. The modeled difference in WSE between
typical August and April flows under existing conditions just upstream of the PFD is
approximately 0.5 feet. The modeled difference in WSE between typical August and 10-year
flood flows is more than three feet.
In its pre-development state, the LPR was dynamic in the horizontal plane, as well. The river
historically migrated across its floodplain, as evidenced by the remnant oxbows in the Fay Field
area. Today, the river is constrained in many areas by urban development, flood walls, and fill.
The LPRRP, together with support by the NRCS sponsored OFRP, seeks to begin restoring this
dynamic and natural riverine environment.
The Pawtuxet River drains an approximately 228 mi2 watershed and, as such, contributes a
significant amount of fresh water into Narragansett Bay. The Pawtuxet River is classified by the
RIDEM as a Class 5 water body under the state’s consolidated assessment and listing
methodology (CALM) which is found in RIDEM’s 2008 Integrated Water Quality Monitoring
and Assessment Report. This classification indicates that the lower Pawtuxet is “Impaired or
threatened for one or more designated uses by a pollutant(s)”. In the case of the lower
Pawtuxet, the Class 5 designation is based on the following impairment criteria:

Impairment to Fish and Wildlife Habitat – Based on benthic-macroinvertebrate
community observations, bioassessments, Cadmium levels, presence of non-native
aquatic plants, and Phosphorous (total) levels

Fish Consumption – presence of elevated levels of mercury in fish tissue

Primary Contact Recreation (swimming) – Presence of elevated fecal coliform

Secondary Contact Recreation – Presence of elevated fecal coliform
The LPR is fairly wide, with a very low gradient and a number of deep pools. In the 4.5-mi.
section of river from the United States Geologic Survey (USGS) gage in Cranston to the PFD,
the river varies from approximately 60 ft to 200 ft wide, with mid-channel depths ranging from 3
ft to 14 ft. The river exhibits very little gradient in this reach, dropping less than 1 ft per mile.
Because of the river’s low gradient and the height of the PFD (approximately 5 ft), the backwater
effect of the dam can extend as far as 4.5 mi upstream from the PFD, depending on river flow.
1.1.2 Site History
As early as 1660, the Pawtuxet River was used to power gristmills and sawmills. Dams were
constructed along the river to support these uses and as a result, the dams prohibited fish
migration upstream. The preclusion of migratory fish passage in the Pawtuxet led to the
enactment of “An Act Regulating the Fishery in the Pawtuxet River” in 1767, which placed
restrictions on dam construction and required fish passage structures on existing dams. The Act
led to the first fish ladder in United States being constructed on the Pawtuxet River.
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Textile mills first appeared on the river in 1794 and by 1829 the river supported 13 such mills,
and was used for mechanically-powered industrial processing and waste disposal. During the
1860s, the RI General Assembly granted the City of Providence permission to pump municipal
drinking water from the Pawtuxet River. In 1868, the City of Providence invested to build the
Pettaconsett Pumping Station along the Pawtuxet River in Cranston. The station opened in 1871,
pumped water up to the Sockanosett Reservoir and down Reservoir Avenue to Providence.
Water quality became an issue before the end of the century and by 1892 a study by the Pawtuxet
River Commission concluded that the river was polluted by sewage discharged from mill
tenements, private homes, farms, and industrial waste from numerous facilities along the river.
The commission recommended that the city relocate its supply to the upper Pawtuxet River prior
to the flow reaching the contamination sources. By this time, the historic fish ladder was no
longer in operation. In 1915, the construction of the Scituate Reservoir began and, in 1926, the
reservoir opened, leading to the abandonment of the LPR being used as a metropolitan water
supply. In 1933 the Pettaconsett Pumping Station was destroyed.
History of Fishery and Water Quality
Migratory fish such as herring and shad have been harvested around the Pawtuxet Falls area for
at least the past several centuries, although Narragansett Indian oral tradition suggests that the
practice is far older. During the seventeenth century wooden weirs were used to capture the
harvested fish (PAL, 2006). The use of fish weirs became so common throughout the state that
the Rhode Island General Assembly passed legislation allowing towns to block the use of fishing
weirs or nets and the construction of new dams in 1719. As demand for industrial power grew,
many dams were built specifically for that purpose. Today, there are more than 140 dams in the
Pawtuxet watershed, the majority of which were built during the 19th century to power mills and
factories.
In 1765, the construction of a dam on the Pawtuxet River, upstream of Pawtuxet Falls in
Cranston was allowed; however, the owners were required to build and maintain fish passage
from April 10 to May 20 annually. The wooden weirs continued to be used to trap fish into the
nineteenth century. Between 1874 and 1894, a fish ladder was present at the then existing timber
dam at Pawtuxet Falls which helped trap and catch the harvested fish (PAL, 2006). In the late
1800’s, visitors from Providence and surrounding communities would often line the Pawtuxet
Bridge to watch the annual springtime fish run over the fish ladder that existed on the timber
dam.
The first waste water treatment facilities in the watershed were constructed in the 1930s and
1940s to accommodate the growing populations of West Warwick and Cranston. These facilities
provided only primary treatment before discharging into the river. The water quality of the
Pawtuxet River has since improved considerably in recent years due to industry changes and
improved operations of the three wastewater treatment facilities within the watershed (PAL,
2006).
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Pawtuxet Falls Dam
There are no known records of when the first dam was constructed at Pawtuxet Falls, located at
the mouth of the river. However, a wooden dam is known to have existed at the same location as
the existing PFD since at least 1870, and probably considerably earlier than that. The dam at
Pawtuxet Falls was bought by the City of Providence from American Wood Paper Company in
1870. The acquisition of the dam occurred at the same time the City of Providence began to
develop the Pawtuxet River as a municipal water supply source.
While its original purpose was to power a mill, the wooden dam at Pawtuxet Falls also prevented
the intrusion of salt water into the river, which was important for the protection of the newly
developed drinking water supply. In addition to preventing salt water intrusion, the dam also
served to mitigate any water level changes in the river that might be associated with the former
municipal pumping at the Pettaconsett Pumping Station located upstream (PAL, 2006). In 1924,
the existing concrete dam structure was constructed by the Providence Water Supply Board,
replacing the previous timber dam.
In 2008, the PRA purchased the PFD and an adjoining parcel on the Warwick side of the river
from the City of Providence. Also in 2008, the PRA commissioned a title investigation,
completed by Martinelli, Capucci and Associates of Warwick, which confirmed that the PRA
holds sole title and control of the dam structure across the entire river, in both Warwick and
Cranston. This title investigation is presented as proof of ownership of the dam as part of the
application form to supplant the Tax Assessors information and is included in Appendix C.
1.1.3
Dam Structure and Hydraulic Function
Flow data for the Pawtuxet River was obtained from the USGS Gage Station 01116000, located
approximately 4.5 miles upstream of the PFD, with a period of record from 1939 to present. The
existing dam is approximately 170 ft long and 5 ft high and consists of three sections constructed
between large bedrock outcroppings in the river (Photograph 1).
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Photograph 1: Westerly view of Pawtuxet Falls Dam from Broad Street Bridge.
(Source: Narragansett Bay Estuary Program)
Flow in the Pawtuxet River is influenced by upstream reservoirs, particularly the Scituate
Reservoir. Minimum in-stream flow releases are required from the Scituate Reservoir during
low flow periods. Highest flows generally occur in April, while lowest flows occur in August.
The average annual flow for the Pawtuxet River based on a 60 year period of record is 352 cubic
feet per second (cfs). During all observed flows, water passes over all three sections of the PFD
and there is no flow control structure on the dam. The width of the river at the dam varies from
163 feet at 140 cfs (median average low flow) to 187 feet at 3,900 cfs (10 year frequency flow).
Mean high water (MHW) is approximately 2.50 ft below the crest of the dam, with mean low
water (MLW) approximately 6.85 ft below the crest of the dam. The mean tidal fluctuation
downstream of the PFD (MHW-MLW) is 4.35 ft.
1.1.4
Geology and Soils
Soils in the vicinity of the project area are generally mapped as gravelly sandy loam, with areas
of urban land (Rector, 1981). The substrate of the vegetated wetlands along the banks above the
river is predominately sandy loam and mucky sandy loam in texture.
The Pawtuxet River is underlain by the Pennsylvanian aged Rhode Island Formation (Hermes, et
al., 1994). The Rhode Island Formation is a member of the sedimentary Narragansett Bay
Group. It is described as a gray to black, fine- to coarse-grained quartz arenite, litharenite, shale,
and conglomerate, with minor beds of anthracite and meta-anthracite. Depth to bedrock varies
throughout the project area, and is exposed in locations adjacent to the existing dam.
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1.1.5
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Wetland Resources
Data obtained through the Rhode Island Geographic Information System (RIGIS) database and
extensive field observations indicate that the majority of wetlands in the project area consist of
open water and deciduous forested swamps. These wetlands are comprised of the LPR (and its
associated floodplain wetlands) and low-lying wetlands subject to runoff from upgradient
sources (refer to Figure 3). The largest wetland system in the project area is the complex located
to the northwest of the Rhodes on the Pawtuxet (Rhodes), adjacent to Fay Field in the area of the
OFRP. This complex consists of forested, emergent marsh, and open water wetland cover types.
Some of the wetlands in the Fay Field complex are remnant river channels, or oxbows. Other
wetlands along the project reach include palustrine open water, emergent marsh, and scrub-shrub
swamp. Most of these wetlands occur on floodplains which appear to receive surface water
inputs only during flood events and which otherwise are hydrologically fed by shallow
groundwater, stormwater outfalls, or small streams.
Although virtually all of the wetlands of the LPR have been anthropogenically disturbed by dam
construction, local filling, hydromodification, fragmentation, and other impacts, they comprise a
large, interconnected complex of great ecological and social importance, the value of which is
increased by the highly urbanized and impervious nature of the surrounding landscape.
Important functions provided by the LPR wetlands include fish and wildlife habitat, flood
storage, recreation, and stormwater treatment.
Refer to Section 1.3.2.3 for detailed information on wetland resources in the project area.
1.1.6 Fisheries
The Pawtuxet River historically provided spawning habitat for several species of migratory
(diadromous) fish, including two species of river herring (Alosa aestivalis and A.
psuedodoharengus), American shad (A. sapidissima) and American eel (Anguilla rostrata).
These ecologically important species have been virtually eliminated in the LPR by the PFD,
while their populations have also been reduced throughout the northeast by similar barriers.
RIDEM’s Strategic Plan states that the Pawtuxet River is capable of supporting populations of
alewife, blue-back herring, and American shad.
Table 1-1 describes fish species that have been found within the LPR, based on RIDEM data
obtained on 2 May 1996.
Table 1-1 Fish Species Found in the Pawtuxet River
Total Length (mm)
Mean (Range)
White sucker
45
233 (83-486)
Brown bullhead
9
202 (155-325)
Common carp
3
564 (535-581)
Bluegill
3
142 (119-181)
White perch
2
216 (206-226)
____________________________________________________________________________________________
Species
Number
Species
Number
Largemouth bass
1
American eel
*
*collected during supplemental sampling
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Total Length (mm)
Mean (Range)
262
285
Data was obtained through personal communication with RIDEM.
1.1.7
Infrastructure
Existing infrastructure within the project area is comprised principally of bridges and floodwalls.
The location of each structure of concern is provided in Figure 4. The Broad Street Bridge is
located just downstream of the PFD. The bridge’s three spans were constructed by incorporating
two large outcroppings of rock ledge.
The south bank adjacent to the PFD consists of a large concrete retaining wall and a natural rock
ledge. When the concrete dam was constructed in 1924, a rock outcropping section of about 40
square feet on the south bank was excavated down to existing grade. The north bank consists of
a rubblestone retaining wall that extends from the Broad Street Bridge west to about 10 ft past
the dam spillway. The south bank wall extends approximately 15 ft upstream before turning
inland. During low flows, the water level is below the bottom of the south bank wall.
Rhodes on the Pawtuxet is an historic building located approximately 2,200 ft upstream of the
PFD constructed on concrete piles along river left (facing downstream). The structure is listed
on the National and State Registers of Historic Places and as a National Historic Landmark. The
existing concrete piles are partially deteriorated and exhibit surficial cracking, however, no
detailed engineering evaluation was conducted of the structure of for this project as the project
will not affect the structural integrity of the structure.
The Warwick Avenue Bridge is located approximately 5,430 ft upstream of the PFD. The
bridge’s concrete piers are protected by a 4 ft deep layer of 8” stone. Additionally, each concrete
pier is further supported by timber pilings.
The Elmwood Avenue Bridge is located approximately 13,400 ft upstream of the PFD. Each
concrete pier has piles that are driven to a minimum depth of 20 ft below existing grade. The
abutment walls appear to be in good condition based on visual inspection, indicating no
significant scour has occurred to date.
The former Conrail Bridge located approximately 7,000 ft upstream of the PFD is no longer in
use. Structural information was not obtained for this bridge. Approximately 200 ft upstream of
the non-functioning Conrail bridge, is a former pedestrian bridge. This bridge has been removed
although the piers have been left in place.
The Amtrak Bridge and I-95 Bridge, located approximately 15,330 and 16,370 ft upstream of the
PFD, respectively, were not analyzed as the proposed partial dam removal would result in an
insignificant change to WSE or velocity at these locations.
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1.1.8
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Sediment
1.1.8.1 Sediment Mobility
Approximately 8,110 yd3 to 16,230 yd3 (6,840 – 13,680 tons) of sediment is transported through
the river system every year (MMI, 2008). Most of the sediment deposits immediately upriver of
the PFD exist in the form of a vegetated point bar and narrow bands of material near the banks.
Most sediment within the LPR is transported during periods of high water flow velocities (i.e.
1.5-year frequency flow). High flow velocities are able to erode and transport larger particles,
accelerating erosion.
As specified in the Feasibility Study (FS), previous investigations have indicated that
depositional zones in the LPR tend to occur on the inside of bends and just downstream of large
pools, as is typical in a lower perennial river systems of this size. The main channel of the river
was found to be scoured with no measurable sediment in the center of the river for approximately
300 feet upstream of the dam.
The conclusion of these findings is that the LPR is actively transporting large quantities of
sediment through the system and over the PFD, which means that the PFD is not serving as a
sediment trap.
1.1.8.2 Sediment Exposure
Much like many urban rivers within Rhode Island, the Pawtuxet River has a legacy of industrial
and urban stormwater discharges that contributed contaminants to the river system that are not
acceptable under current regulatory standards. While industrial discharges are now largely
compliant with regulatory standards, problematic contribution continues today in the form of
run-off from paved surfaces in the form of Polycyclic Aromatic Hydrocarbons (PAHs) and
certain metals. The accumulation of these non-point source constituents often poses a problem
when discussing human health risk relating to exposure to urban riverine sediment as the
sediment will often exceed regulatory residential risk standards (i.e. RIDEM Residential Direct
Exposure Criteria [RDEC] and Industrial/Commercial Direct Exposure Criteria [I/C DEC]).
In addition to exposure issues with sediment contamination associated with urban runoff, the
LPR was home to the Ciba-Geigy facility (Ciba) which began in 1930 as the Alrose Chemical
Company. The property was purchased in 1954 by the GEIGY Chemical Company of New
York, and was then merged with the Ciba Corporation in 1970 (RCRA Facility Investigation,
Pawtuxet River Corrective Measures Study, 1996). Industrial discharge activities at Ciba likely
contributed various constituents, including Volatile Organic Compounds (VOCs),
Polychlorinated Biphenyls (PCBs), copper, lead, and zinc to the LPR River sediment load.
Further information regarding the clean-up and additional sampling associated with this
discharge is presented in Section 1.3.1.
Potential human exposure to the LPR sediment originates from recreational activities associated
with transitory activities such as canoeing, kayaking, and walking. However, there is the
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possibility that children and others may come into contact with sediment during fishing and other
activities along the river bank. Potential human exposure to sediment along the banks occurs
primarily during warm weather months, which typically coincides with low water elevations.
Potential human contact with riverine sediment also occurs in floodplain areas where sediment
deposition occurs during sediment transport events (i.e. ≥1.5-year frequency flow). These
deposition areas are part of the active river system that continually scours and deposits as part of
frequent sediment transport events.
Present impairments to the water quality of the LPR are listed in the state’s CALM found in
RIDEM’s 2008 Integrated Water Quality Monitoring and Assessment Report. The Pawtuxet’s
Class 5 classification indicates that the lower Pawtuxet is “Impaired or threatened for one or
more designated uses by a pollutant(s).” In the case of the lower Pawtuxet, the Class 5
designation is based on the following impairment criteria:
 Impairment to Fish and Wildlife Habitat – Based on benthic-macroinvertebrate
community observations, bioassessments, Cadmium levels, presence of non-native
aquatic plants, and Phosphorous (total) levels
1.2

Fish Consumption – presence of elevated levels of mercury in fish tissue

Primary Contact Recreation (swimming) – Presence of elevated fecal coliform

Secondary Contact Recreation – Presence of elevated fecal coliform
Methodology
In order to fully address concerns expressed by RIDEM in our pre-application discussions, the
PMT has evaluated the following potential impacts of the restoration:

The potential that reduced WSEs will lead to an increased human contact rate to
riverine sediment that may contain constituents above RDEC.

The potential that increased velocities will increase the frequency of sediment
transport events which might be deposited in Pawtuxet Cove, increasing the need for
navigational dredging maintenance.

The potential that reduced WSEs may negatively impact wetlands adjacent to the
LPR.
This section of the application narrative provides the regulatory agencies with the methodology
utilized to address these concerns. For the purposes of this section “exposure” refers to
riverbank areas that will become exposed under August proposed mean flow conditions and that
are not currently exposed under similar flows.
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To satisfy regulatory requirements regarding sediment exposure and mobility, as well as
proposed water level changes, the applicant sequentially completed the following:
1. Reviewed existing data from the sources listed in Section 1.3.1;
2. Evaluated EPA/RIDEM clean-up goals and objectives at the Ciba-Geigy site to use as a
benchmark for potential sampling and remediation requirements;
3. Identified areas along river banks associated with potentially significant human use;
4. Collected supplementary bathymetric data along 34 transects (as requested by RIDEM)
from the PFD up to I-95 where there will be minimal proposed change in WSEs during
low flow events resulting from this project;
5. Collected an additional 34 grain size samples to supplement data from the FS and CibaGeigy reports for sediment transport and exposure analysis per RIDEM approved
Permitting Strategy memorandum dated 29 January 2009 (Appendix D);
6. Refined and updated HEC-RAS model of existing conditions within the lower Pawtuxet
system to compute existing and proposed WSEs and flow velocities from Pawtuxet Cove
to I-95;
7. Utilized grain size information and HEC-RAS output velocities to compute critical shear
stress, existing shear stress, and proposed shear stress for the partial breach scenario;
8. Analyzed shear stress data to determine areas of potential sediment transport and
determine the need for potential sediment stabilization or removal based on whether or
not there would be a marked increase in mobilization potential and increased human
exposure as a result of the proposed project; and
9. Delineated and assessed wetlands within the project area. Utilized topographic data and
HEC-RAS information to determine whether changes to WSEs would impact adjacent
wetlands.
10. Performed sediment sampling and analysis in areas proposed for dredging and disposal,
and potential sediment exposure areas.
1.2.1
Existing Data Review and Team Qualifications
Numerous projects and investigations have been conducted within the project area that provide
relevant data and information that serve as a base for this application. Specifically, the
remediation effort at the Ciba Geigy facility (Figure 5), USACE dredging project at Pawtuxet
Cove (Figure 6), the MMI and Kleinschmidt reports, and the 2006 PAL report (Appendix B).
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Professionals from the following organizations contributed to this application:
Federal
 USDA – Natural Resources Conservation Service
 National Oceanic and Atmospheric Administration
 U.S. Fish and Wildlife Service
 U.S. Environmental Protection Agency
State


R.I. Department of Environmental Management
R.I. Coastal Resources Management Council
Non-Governmental
 Pawtuxet River Authority (Project leader and administrative entity)
 Narragansett Bay Estuary Program (Project manager and outreach)
 Save The Bay
 American Rivers
Engineering Consultants
 Kleinschmidt Associates
 Milone & MacBroom, Inc.
 EA Engineering, Science, and Technology, Inc.
1.2.2 Field Effort
Data collected at each transect along the river included visual identification of existing scour or
deposition areas, sampling of sediment for grain size analysis, site photography, identifying
public use areas, and identifying active flood plain areas greater than 15-ft in width (as measured
perpendicular to flow). Field data was transcribed onto Field Forms, which are included in
Appendix E. The choice to record the presence of a >15-ft wide floodplain area was included as
a general notation was not applied to the analysis of subsequent results.
1.2.2.1 River Elevation Data
The field effort to identify areas of human use along the riverbank, collect elevation data, and
obtain grain size samples took place on 29 and 30 April 2009 as well as on 4, 6, and 7 May 2009
by EA Engineering, Science, and Technology, Inc. (EA). Elevation data were collected along 34
transects (Transects #2 through #35), the locations of which were identified prior to mobilization
utilizing existing photogrammetry from the City of Cranston and elevation data from the FS.
Based on a request from RIDEM, transects were spaced at least approximately every 500-ft east
of Elmwood Ave, and every 1000-ft west of Elmwood Avenue. Precise locations were
determined based on proximity to potential areas of increased scour, deposition, or exposure.
Vertical elevations were collected based on water depth and fixed horizontally utilizing a Global
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Positioning System (GPS) unit. Elevations were then corrected using USGS Gage data and
NGVD29 benchmark data.
1.2.2.2 Sediment Sampling
A sediment sample was collected from each transect for grain size analysis. The sampling
locations were selected based on proximity to potential areas of increased scour or exposure.
These locations often occurred along the inside bend of the river as these are depositional areas
where fine-grained sediments accumulate. Seven additional samples were also collected from
other regions of the river in order to fully characterize the chemical constituents of the existing
sediment. The locations of the transects and sediment samples are provided in Figures 7 and 8.
Depending on the water depth, samples were collected using a Ponar dredge, hand auger, or push
core. Ponar sampling is suitable for deep or fast moving water; as they have top screens and side
plates to prevent sample loss during retrieval. Sediment was collected from the top six inches of
river bottom to characterize surficial grain size data. For chemical analyses, sediment was
collected top four feet of river bottom for proposed dredge areas and the top six inches for
sediment exposure areas. Samples were then put in laboratory provided glass jars and submitted
to ESS Laboratory for analysis.
1.2.2.3 Wetland Assessment and Identification
Wetlands in the project area were described and assessed utilizing field-delineations, RIGIS data,
published soil data, and the Pawtuxet River Wetlands and Potential Impacts memorandum
prepared by the National Oceanic and Atmospheric Administration (NOAA) Restoration Center,
dated 24 August 2007 (Appendix B).
Staff from the NOAA’s Restoration Center and the Narragansett Bay Estuary Program conducted
a field reconnaissance event on 7 April 2005 to verify mapped wetlands and associated
vegetation, landscape, and micro-topographic features. The reconnaissance targeted some of the
broader mapped wetlands, focusing on specific areas within these wetlands where a hydraulic
control may be present and/or the extent these wetlands are hydrologically affected by changing
water levels of the nearby the LPR. Five wetland areas were visited, although one of the mapped
wetlands and floodplain off Vine Avenue (approximately 1.5 miles upriver from the dam) has
been converted into a stormwater management basin as part of an industrial jewelry
manufacturer.
Wetlands within the RCA were field-delineated by EA wetland scientists on 10 and 11 February
2009. Criteria for identifying state regulated wetland resource areas are provided in the RIDEM
Rules and Regulations Governing the Administration and Enforcement of the Freshwater
Wetlands Act (Rules) (RIDEM, 2007). In addition, the RIGIS database was used to obtain
estimated mapping of wetlands for the LTRA. The RIGIS wetland mapping was ground-truthed
to verify its accuracy within the project area. The Soil Survey of Rhode Island was used to
identify mapped hydric soils as an indicator of wetlands, and compare the mapped hydric soil
units to the RIGIS wetland mapping. As described in the NOAA report, RIGIS wetland
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information was also used to conduct a field reconnaissance and to target representative wetlands
along the LPR in order to further assess wetland features and ecological functions. All of the
above information was used for the wetlands assessment and descriptions provided in this permit
narrative.
To investigate the frequency that adjacent wetlands are inundated by the Pawtuxet, cross section
figures were developed. The cross sectional diagrams were created using 2-ft interval
topographic data obtained from the City of Cranston, river bathymetry collected by EA (as
described in Section 1.2.2.1), and water level data generated with the HEC-RAS model (as
described in Section 1.2.3). Wetland maps were overlaid onto the cross sections to determine the
interaction of the wetland resource areas with the river. The cross sections compare the existing
high and low flow conditions (mean April and mean August water levels, respectively) to the
proposed high and low flow conditions after partial dam removal. In addition, the existing 1.5year and 2-year frequency flow water levels were compared to the proposed 1.5-year and 2-year
frequency flow water levels to determine the change in flood elevations and resultant inundation
frequency of the adjacent floodplain areas.
1.2.3
Hydrology and Hydraulic Analysis
A HEC-RAS model study was designed to perform a one-dimensional, steady flow model of
existing and proposed conditions upstream and downstream of the PFD location (Appendix F).
The HEC-RAS model was used to investigate sediment transport, stream bank stabilization
requirements, calculate fish passage requirements for target species, and perform a hydraulic
analysis of the WSEs for various design storms.
The HEC-RAS model was developed to represent localized flow under existing and proposed
conditions in the area from the PFD upriver to I-95 and downstream of Pawtuxet Cove. This
study incorporated cross-section data obtained from the Federal Emergency Management
Agency Flood Insurance Study (FEMA-FIS) of the Pawtuxet River and was supplemented with
cross-sections developed by Kleinschmidt, MMI, and 34 cross-sections collected by EA at the
request of RIDEM. These cross-sections were measured at sufficient intervals to sufficiently
analyze the hydraulic conditions of the proposed final design.
Hydrology
The hydraulic analysis modeled the 1.5-, 2-, 10-, 50-, 100-year, and 500-year frequency flows in
order to determine potential wetland impacts and channel bed and bank stabilization
requirements. The 10-, 50-, 100-year, and 500-year frequency flow discharge values modeled
are based on data published in the FEMA-FIS for the Cities of Warwick and Cranston, dated
1991 and 1984, respectively. A Log-Pearson Type-III frequency curve was used to estimate the
1.5-year and 2-year frequency flows.
The HEC-RAS model was also developed to model flow conditions during the months of April
and August to evaluate impacts to fish passage. Mean daily flow values were acquired from the
USGS gage and represented data from 1939 to 2009. The average monthly flows at the gage for
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the April, and August months are 600 cfs and 174 cfs, respectively. This flow was then increased
in proportion to the increase in drainage area from the gage location (200 mi2) to the PFD
location (228 mi2). Table 1-2 shows the discharge flows at the PFD for the flows analyzed.
Table 1-2 Discharge and Storm Recurrence at Pawtuxet Falls Dam
Recurrence
500-YR
100-YR
50-YR
10-YR
2-YR
1.5-YR
Mean April
Mean August
Discharge (cfs)
23,000
8,300
6,200
3,900
2,004
1,723
684
198
Modeled Flows
The HEC-RAS model study was used to evaluate needs for potential channel/bank stabilization
and to ensure that hydraulic requirements for fish passage were met. Flows corresponding to a
variety of flow regimes were used for the evaluation. Fish passage requirements considered the
average flow over the migration period of the target species, while channel stabilization and the
hydraulic analysis focused on peak flows. Analysis for potential wetland impacts evaluated
peak, average, and low flow conditions.
Average low tide and high tide WSE downstream of the PFD were utilized to establish initial
water surface data at the most downstream modeled cross-section (river station 130, which is 70
ft downstream of Broad Street Bridge) for the mean April, mean May, mean August, 1.5-, 2-,
10-, 50-, 100-year, and 500-year frequency flow recurrence intervals. The MMI HEC-RAS
model used corresponding storm surge heights for the downstream water levels of the storm
events 10-year and greater. EA modified the boundary conditions to a more conservative value
and used mean low water elevations. The downstream boundary condition of average low tide is
-1.58 ft and the average high tide is 2.33 ft NGVD 29.
Manning’s roughness coefficients presented in the MMI HEC-RAS model were utilized in this
analysis. Manning’s roughness coefficient for the main channel was 0.050 for existing
conditions. Manning's roughness for right out of bank and the left out of bank were 0.08.
In order to evaluate the proposed conditions within the model, approximately 150 ft of the in-line
structure corresponding to the PFD was removed. The Manning's roughness coefficients for the
proposed conditions were kept consistent with the existing model.
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Fish Passage Requirements
The HEC-RAS model was also used to determine the water depths and flow velocities for the
proposed conditions at the PFD location during the target fish migration period.
The modeled values can be compared to target species' passage requirements. Fish passage
requirements for the target species (American shad, alewife, and blueback herring) are shown in
Table 1-3.
Table 1-3 Fish Passage Hydraulic Requirements
Species
Migration
Min. Water Depth
Cruising Speed
Sustained Speed
Burst Speed
Units
Months
in.
ft/s
ft/s
ft/s
American
Shad
Apr – June
7-9
2.8
7.6
14.8
Alewife
Apr - June
7-9
2.8
4.8
6.8
Blueback
Herring
Apr – July
7-9
2.8
4.8
6.8
Channel velocities during the average flow of the fish migration period were deemed acceptable
if less than the burst speed for short distances and sustainable speed for long distances. The
above table was also used for criteria for minimum water depth.
Hydraulic Analysis
The purpose of the hydraulic analysis is to determine the change in WSEs expected to occur
from the proposed partial removal of the PFD and to assess the potential for negative impacts.
Appendix F presents the results of the HEC-RAS modeling for the existing and proposed
conditions throughout the LTRA. Upstream of the dam, the WSEs decrease with partial removal
of the dam. Downstream of the dam, WSEs do not change after partial dam removal.
The downstream boundary water elevation condition for the HEC-RAS model was assumed to
be -1.58 ft NGVD 29, mean low water. Mean low water was chosen as a conservative analysis
as water elevation changes upstream of the PFD are more likely to be greater under low tides due
to less back water effects from a low tail water condition.
1.2.4
Sediment Mobility Analysis
To evaluate sediment transport for the partial dam removal proposed condition, analysis of
critical shear stresses was employed under a “worst-case” scenario using HEC-RAS software.
The scenario used a low tide tail water condition, therefore ensuring that velocities were not
depressed by a higher tail water condition. A Shields (1936) analysis was performed using the
D50 sediment sizes to estimate the threshold (i.e., critical shear stress) for uncovered sediment
erosion and/or transport, as further discussed in Section 1.3.4.
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Sediment sampling was conducted on the LPR, as described in Section 1.2.2.2. Samples from
central locations in the channel indicated that coarse gravels were present in the channel thalweg,
while samples from banks indicate the presence of fine-grained sediments which are most likely
to move under low flow conditions, or as suspended or wash load.
Critical shear stress is the value of shear stress which initiates movement of a particle. Accepted
relationships include the Shields Curve, which predicts movement of various grain diameters for
a given shear stress. Other relationships have also been created for given data sets.
The average channel shear stress is defined as:
τ =γRS
(1)
Where: τ = shear stress
γ = density of water, 62.4 pounds per cubic foot
R = hydraulic radius of the channel
S = energy grade line (slope)
Similarly, the critical shear velocity is calculated as:
(2)
where:
τb = shear stress at the boundary
ρ = is the density of the fluid.
A Shields (1936) analysis was performed using the D50 sediment sizes, as determined by the
sediment sampling effort, to estimate the threshold (i.e., critical shear stress) for uncovered
sediment erosion and/or transport. Critical or permissible shear stress, τc, for stability of a
particle having a diameter, d is calculated from the following equations:
1
 
v

 s 

 
 3 
 gd



 0 .6
(3)
τ* = 0.22β + 0.06 x (10-7.7β)
(4)
τc = τ*(γs – γ)d
(5)
where:
γs
= Specific weight of sediment (9,807*SG), N/m³
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γ
d
g
SG
v
τc
=
=
=
=
=
=
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Specific weight of water (9,807), N/mз
Particle diameter, m
Acceleration of gravity, m/s²
Specific gravity (fine silt – 1.25, medium sand – 2.65)
Kinematic viscosity of water (1.307 x 10-6 @ 10° C), m²/s.
Critical or permissible shear stress
Critical shear stress values computed using the equations above are expressed in N/m2 units.
Results are multiplied by 0.02088 to convert units to lb/ft2. A table of critical shear stress,
existing shear stress, and proposed shear stress can be found in Appendix G for a variety of flow
conditions.
In examining the magnitudes of critical shear stresses, shear conditions in excess of the critical
shear stress generally are considered to erode bed clasts, while shear stress conditions less than
the critical shear stress are considered to either transmit the material delivered to them from
upstream or accrete material, forming bars, mud flats or other depositional features. This is
because the critical shear stress to initiate movement is generally considered larger than the shear
stress required to maintain the movement of sediment particles.
1.2.5
Sediment Exposure Analysis
Public Access Identification
The anticipated drop in water levels behind the PFD will result in a greater potential for human
exposure to sediment during low flow events as a result of the proposed project. RIDEM has
indicated a concern regarding the chemical constituents within existing sediment loads.
Therefore, the identification of areas that will exhibit a disproportionate increase in human
exposure based on public use is necessary. Aerial photography, road/trail maps, anecdotal
evidence, and field observations were used to identify areas of human use. Areas directly
adjacent to residential dwellings were considered potential human use areas, as were
canoe/kayak launch areas and trail access areas. While human use is certainly not isolated to
these locations, for the purposes of this investigation, high use areas were singled out for further
investigation.
Direct Exposure Analysis
Once potential high use areas were identified, further investigation into how the proposed project
would affect the high use areas was performed. Specifically, those areas that would likely
experience a water level change of <6-in. (i.e. west of Elmwood Avenue) during low flow
conditions were not considered for further investigation based on the anticipated minimal water
level change. Areas expected to incur a water level change of >6-in. during low flow conditions
were evaluated based on both human use and existing bathymetry to determine the horizontal
extent of the additional exposure area resulting from the proposed project. In other words, if the
bathymetry indicated that the water level change would occur over a steeply sloped area, then the
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horizontal exposure area was expected to be relatively small as compared to a gently sloped area
that would exhibit a greater horizontal exposure resultant from a drop in water levels.
With regard to analysis of the proposed conditions, the direct exposure analysis also investigated
the change that was expected to occur in the new exposure areas. Specifically, if a new exposure
area would experience scour or accretion under proposed frequent higher flow events (i.e. 1.5year frequency flow), then this area would not be considered for further investigation for
stabilization/capping as normal river processes would continue to alter this exposure area.
Discussion concerning the results of this analysis is included in Section 1.3.5.
1.3
Results
1.3.1
Existing Data Review
Ciba-Geigy
The Ciba investigation and remediation effort relevant to this application involves the sediment
testing and remediation effort. The history, methodology, and results of the most recent testing
event are contained within the Sediment Sampling Report for the Pawtuxet River, Former CibaGeigy Facility, Cranston, RI, (Ciba Specially Chemicals Corp., 2003) which is provided in
Appendix B.
The following excerpt from that report summarizes project history relating the sediment
remediation effort and the sampling approach for the 2002 sampling event:
“As part of the overall Interim Remedial Measure (IRM) that Ciba is implementing at the
Site, a voluntary sediment IRM was conducted during the period October 12, 1995
through January 10, 1996. The sediment IRM was conducted according to the
procedures presented in the Conceptual Design Work Plan, Cranston Site, Cofferdam
Interim Remedial Measure (Work Plan) that was submitted to USEPA, RIDEM, and the
USACE in May 1995. Over 2,225 tons of contaminated sediment were excavated from
the Pawtuxet River and replaced with clean sand during the Sediment IRM. The
excavated area contained a sampling location where high concentrations of PCBs were
measured, as well as the only location in the Upper or Lower Facility reached where 4Chloroanaline was measured. When completed the Sediment IRM achieved its primary
objective of excavating and disposing of visually contaminated river sediment from the
Former Cofferdam Area.
Post-excavation sampling of river sediment was required by EPA/RIDEM. This
requirement was fulfilled in November 2002, with the results contained in this report.”
[Appendix B]
Table 1-4 shows data obtained from the 2002 sampling effort report. Only those analytes which
exceeded RIDEM Direct Exposure Criteria (DEC) are shown. In addition, data obtained from
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the U.S. Army Corps of Engineers’ Environmental Assessment, entitled Pawtuxet Cove,
Cranston and Warwick, Rhode Island, Federal Navigation Project, Maintenance Dredging, June
2004 is included in Table 1-4. Sediment sampling for this project was performed in Pawtuxet
Cove in 1994. Full sediment sampling data is presented in Appendix H. Refer to Figures 7 and
8 for sediment sample locations.
Table 1-4 2002 Ciba Sediment Sampling Results
ppm
ppm
ppm
ppm
ppm
ppm
ppm
1994
Pawt.
Cove
BCOMP
Max.
ppm
VOCs
Chlorobenzene
210
10,000
0.91
360
0.66
ND
N/A
N/A
N/A
Inorganics
Arsenic
Chromium
Lead
7.0
390
150
7.0
10,000
500
N/A
N/A
313
N/A
N/A
393
N/A
N/A
270
N/A
N/A
49.1
12
410
500
4.0
82
120
5.0
35
40
0.9
7.8
3
2.4
8.6
0.58
1.4
0.76
0.27
0.4
0.8
3.7
2.6
6.6
0.56
1.7
0.79
0.24
0.9
7.8
5.9
4.1
8.4
0.64
4.3
0.96
0.29
0.8
10,000
3.3
2.1
3.6
0.44
0.72
0.30
0.10
0.9
78
2.1
1.5
3.8
0.3
4.3
0.99
0.29
0.4
780
5
3.5
7.9
0.64
1.9
1.1
0.38
0.4
0.8
0.88
0.47
1.3
0.13
ND
0.061
ND
0.9
7.8
3.4
2.2
4.2
0.46
ND
0.27
0.17
9.8
5.8
ND
1.3
U
U
U
U
U
U
DEM
Resid.
DEC
DEM
I/C
DEC
2002
Upstream
Max.
2002
Upper
Fac.
Max.
2002
Lower
Fac.
Max.
2002
Downstream
Max.
1994
Pawt.
Cove
A-COMP
Max.
Contaminant
PAHs
Benzo(a)anthracene
Benzo(a)pyrene
Benzo(b)fluoranthene
Benzo(g,h,i)perylene
Benzo(k)fluoranthene
Chrysene
Dibenzo(a,h)anthracene
Indeno(1,2,3cd) pyrene
PCBs
PCB-1248
10
10
ND
170
PCB-1254
10
10
0.25
43
ND = Not detected above method reporting limits
N/A = Not analyzed
U = Results unavailable
Blue cells = Exceeds RIDEM RDEC
Orange cells = Exceeds RIDEM I/C DEC
1994
Pawt.
Cove
C-COMP
Max.
ppm
____________________________________________________________________________________________
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June 2010
Conclusions gained from the 2002 Ciba sampling effort indicate that RIDEM and EPA required
no further remediation of sediments (channel or bank). As no additional information was
available within the RIDEM files, we conclude that EPA/RIDEM agreed that sediment
remediation goals within the LPR were satisfied. This record indicates that EPA/RIDEM
determined at that time that the condition of sediment in the LPR did not pose sufficient human
or ecological risk to warrant further action.
In general, the sediments of the LPR have been characterized as predominantly coarse grained.
In correspondence to RIDEM dated 29 January 2009, the project proponents proposed sampling
sediment at locations along the LPR for grain-size analysis. In this correspondence it was stated
that if the results of the grain size analysis indicated that the sample is predominantly fine
sediment (i.e. finer than 120 sieve opening) then a chemical analysis would be performed. For
all samples taken, TR-2 through TR-35, the grain sizes were predominantly coarser than a 120
sieve opening. However, the PMT (with concurrence from RIDEM) elected to collect samples
for chemical analyses to adequately characterize chemical constituents found in the LPR (refer to
Section 1.3.2.2 for results).
USACE Pawtuxet Cove Dredge Application
The US Army Corp of Engineers (USACE) prepared an Environmental Assessment for
maintenance dredging in Pawtuxet Cove in 2004. The Cove was last dredged in 1966 and
required maintenance dredging again by 2004. The information contained within the regulatory
materials indicated that during the 38-year gap between dredging a total of 90,000 yd3 of
material had accumulated in the cove that varied from silty sand to silt with trace amounts shells
in the majority of the samples. Assuming dredge depths were similar for the 1966 and 2004
dredge events, then 2,368 yd3 of material was deposited per year within the cove. Refer to
Table 1-4 for analytical results from the 1994 sediment sampling.
Previous Studies and Outreach for the Proposed Project
An initial evaluation of fish passage in the Pawtuxet Anadromous Fish Passage Restoration
Project Feasibility Study was completed by Kleinschmidt Associates (KA) and Water Resource
Consultants in July 2005. The Final FS was completed by MMI in 2008. The FS included a
revision of the previously developed hydraulic model of the river system to reflect both the
FEMA model of the river as well as the structure of the PFD. The FS produced a preliminary
sediment stability analysis to assess potential sediment movement and management measures
that may be necessary if the dam were altered. The FS concluded that partial removal of the dam
was the preferred alternative to restore river ecology and fish habitat.
The FS also concluded that in the case of the PFD, upstream sediment accumulations were
observed to be minimal when compared to the volume of material one would expect this
watershed to generate. Results of the sediment sampling and hand probe evaluation completed in
the FS revealed some accumulated sediments upstream of the dam, particularly along the left
(north) bank. However, there is no significant sediment wedge along the rear side of the
spillway.
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June 2010
The volume of accumulated sediment upstream of the dam was estimated by MMI to be
2,200 yd³, similar to the 2004 KA estimate of 2,100 yd³.
Since the alternatives analysis discussion began in 2003, the project has hosted three large public
meetings regarding the project. The meetings were held during the evening in the community
before, during, and after the process of alternative identification. The meetings discussed
sediment mobility and exposure issues, and engaged citizens by meeting with community
groups, local boards and commissions, RIDEM, local business owners, and riverfront property
owners.
1.3.2 Field Effort
1.3.2.1 River Elevation Data
River elevation data was collected from 34 transects along the LPR (Figure 7). Depending on
river width at each transect, depth to river bottom elevations were taken at four to six points
across the transect. River bottom elevations were then corrected using benchmarks located
adjacent to the river and data obtained from the USGS gage upstream. River bottom elevations
ranged from -5.1 ft NGVD29 at the deepest point, to 6.9 ft NGVD29 along the higher banks in
the upper reaches of the project area (Table 1-5).
Table 1-5 River Bottom Elevations
River Bottom Elevations (NGVD29) (ft)
Transect Point
Transect
1
2
3
4
5
6
Transect 35
6.9
4.5
3.6
3.0
--
--
Transect 34
6.8
2.3
0.9
1.2
1.7
4.6
Transect 33
4.9
4.7
4.6
2.6
--
--
Transect 32
5.2
2.2
3.2
3.3
3.2
--
Transect 31
3.6
3.3
3.0
2.7
4.4
--
Transect 30
5.2
3.2
2.5
3.9
--
--
Transect 29
3.7
-0.4
-0.6
1.6
3.5
5.6
Transect 28
3.0
0.8
0.9
2.5
3.6
--
Transect 27
6.2
2.3
-0.1
0.0
3.6
--
Transect 26
4.8
4.6
4.0
2.9
4.9
--
Transect 25
4.5
2.0
1.5
2.3
6.5
--
Transect 24
4.4
2.4
1.7
1.3
3.5
--
Transect 23
4.0
2.2
3.1
3.6
5.6
--
Transect 22
5.1
0.4
-5.1
-3.5
2.5
--
Transect 21
2.0
0.3
1.5
1.9
4.3
--
Transect 20
6.1
2.5
3.0
3.0
5.4
--
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June 2010
River Bottom Elevations (NGVD29) (ft)
Transect Point
Transect
1
2
3
4
5
6
Transect 19
-0.4
-1.4
-1.3
-1.6
2.3
--
Transect 18
4.2
1.0
1.0
1.6
2.3
--
Transect 17
6.2
2.9
0.9
-0.1
5.9
--
Transect 16
4.3
2.9
2.5
1.5
2.5
5.0
Transect 15
-0.7
-1.1
-0.1
3.5
5.6
--
Transect 14
0.3
-0.3
-0.7
0.5
4.9
--
Transect 13
1.9
1.9
-1.3
-1.8
3.2
--
Transect 12
3.1
2.3
0.5
0.5
1.2
--
Transect 11
2.4
0.9
0.2
0.1
2.8
--
Transect 10
0.9
0.0
-1.8
-2.2
1.4
--
Transect 9
0.3
-1.2
-0.8
-1.7
-1.1
-0.8
Transect 8
-0.2
-1.0
-1.6
-0.6
1.3
4.8
Transect 7
2.6
2.0
1.2
-1.3
0.7
--
Transect 6
4.4
2.5
0.6
-0.7
-2.4
-2.9
Transect 5
-2.1
-1.2
-1.5
1.3
4.4
--
Transect 4
-0.8
-1.4
-2.8
-2.1
1.4
--
Transect 3
0.1
0.0
0.3
-1.7
-0.4
3.8
Transect 2
2.0
-4.5
-2.9
-1.5
0.3
--
1.3.2.2 Sediment Sampling
Physical and chemical results are summarized in Tables 1-6 and 1-7, respectively. Locations of
transects and sediment sampling locations are presented in Figures 7 and 8. Refer to Appendix
H for complete grain-size and chemical analyses results.
Table 1-6 Sediment Grain Size Results
Transect
Sample
Transect 35
Transect 34
Transect 33
Transect 32
Transect 31
Transect 30
Transect 29
Transect 28
Transect 27
Transect 26
left bank
middle
middle/right
left bank
middle/left
middle/left
right bank
right bank
right bank
right bank
Grain Size
USCS Classification
(SP) poorly graded sand
(GW) well-graded gravel with sand
(SM) silty sand
(SW) well-graded gravel with sand
(SM) silty sand
Percent Fines
1.2%
0.0%
0.7%
15.2%
0.1%
0.1%
3.0%
0.2%
2.3%
17.1%
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June 2010
Transect
Sample
Transect 25
Transect 24
Transect 23
Transect 22
Transect 21
Transect 20
Transect 19
Transect 18
Transect 17
Transect 16
Transect 15
Transect 14
Transect 13
Transect 12
Transect 11
Transect 10
Transect 9
Transect 8
Transect 7
Transect 6
Transect 5
Transect 4
Transect 3
Transect 2
left bank
right bank
right bank
left bank
right bank
left bank
right bank
left bank
right bank
left bank
right bank
right bank
right bank
left bank
left bank
right bank
left bank
right bank
right bank
left bank
left bank
left bank
right bank
left bank
Grain Size
USCS Classification
Percent Fines
(SP-SM) poorly graded sand with silt
(SM) silty sand
(SM) silty sand
(SW-SM) well-graded sand with silt
(SM) silty sand
no classification - sample was all organic material
(SW) well-graded sand with gravel
(SM) silty sand
1.7%
6.4%
1.4%
5.1%
19.5%
7.7%
6.8%
10.2%
16.9%
6.3%
15.2%
6.6%
7.1%
1.4%
1.1%
5.5%
14.5%
10.0%
11.5%
9.5%
2.7%
0.3%
16.8%
0.3%
Table 1-7 Chemical Analysis Results
Analytes in Exceedance
(mg/kg)
2010 Sample ID
Dredge 1
Dredge 2
EXP 1
EXP 2
Arsenic
ND
ND
ND
21.6
Beryllium
1.89
0.9
1.61
1.25
Lead
118
87.9
113
233
Aroclor 1248 (PCB)
0.555
6.98
13.8
ND
TPH
922
713
751
218
Benzo(a)pyrene
0.534
ND
ND
ND
Bis(2Ethylhexyl)phthalate
55.9
11.7
0.855
0.798
Chrysene
0.746
0.648
ND
ND
Notes: Orange Highlight = Analyte concentration exceeds I/CDEC
Blue Highlight = Analyte concentration exceeds RIDEM RDEC
ND
= Not detected above Method Detection Limit
EXP 3
EXP 4
EXP 5
EXP 6
4.3
0.94
106
2.08
264
ND
0.695
0.265
42.3
1.02
300
ND
ND
ND
ND
ND
ND
1.41
63.4
ND
63.7
0.329
ND
0.424
ND
1.32
59.4
0.0824
137
0.327
5.69
0.458
The sediment sampling analytical results are consistent with other samples taken from the LPR
and surrounding areas in the previous investigations described in Section 1.3.1. In addition, the
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June 2010
results are consistent with sediment samples taken in the Blackstone and Woonasquatucket
Rivers, two urban rivers in Rhode Island where similar fish passage restoration projects are
occurring. See Section 2 for proposed mitigation activities to address RIDEM Direct Exposure
exceedances.
1.3.2.3 Wetland Assessment and Identification
All wetland delineations and assessments occurred prior to the flooding of March 2010 and as
such, existing conditions may have changed. The field-delineation (see Section 1.2.2.3 for
methodology) of the RCA identified a series of Forested Wetland/Emergent Marsh wetland
complexes on both sides of the LPR (Photograph 2). The forested components of these
complexes are dominated by red maple (Acer rubrum) trees. Soils generally consist of six inches
of black (10YR 2/1) mucky sandy loam, underlain by brown (10YR 5/3) subsoil. Understory
vegetation includes arrowwood (Viburnum dentatum), sweet pepperbush (Clethra alnifolia),
greenbrier (Smilax rotundifolia), and poison ivy (Toxicodendron radicans). The marsh
components generally consist of reed canary grass (Phalaris arundinacea), common reed
(Phragmites australis), cinnamon fern (Osmunda cinnamomea), sensitive fern (Onoclea
sensibilis), skunk cabbage (Symplocarpus foetidus), and sphagnum moss (Sphagnum sp.). Soils
in these areas consist of a 12-in. sapric organic horizon underlain by a gray (2.5Y 5/1) silt loam
subsoil.
11 February 2009
Photograph 2. Forested Wetland/Emergent Marsh Complex along the Pawtuxet River.
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June 2010
The wetland complexes immediately upstream of the dam in the RCA are located on floodplains
which appear to receive surface water inputs only during flood events. Numerous outfalls were
observed in the wetlands in the RCA. These outfalls appear to supply a constant source of base
flow to the wetlands, as evident by the defined stream channels dominated by skunk cabbage and
sphagnum moss, both of which are obligate wetland species that require constant water sources
(Photograph 3). These up-gradient surface water inputs, in conjunction with shallow
groundwater, appear to be the controlling hydrologic component in these wetlands.
A stream was delineated approximately 1,200 feet upstream of the PFD along river right. This
stream flows northeasterly through a culvert underneath Post Road, adjacent to a warehouse
complex, and into the LPR. Immediately adjacent to Post Road the stream is greater than 10 feet
wide. From approximately 25 ft northeast of Post Road to the river, the stream is less than 10 ft
wide.
Skunk cabbage and
sphagnum moss.
Photograph 3. Obligate wetland species present in outfall drainage paths.
Hydric soils mapped within these wetlands include Ridgebury, Whitman, and Leicester
extremely stony fine sandy loam (Rf), Rumney fine sandy loam (Ru), and Adrian mucks (Aa)
(Rector, 1981). Ridgebury stony fine sandy loam is nearly level, poorly to very poorly drained
soils along waterways and depressions. The surface layer is typically black, fine sandy loam with
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June 2010
underlying grayish-brown to brown fine sands to a depth of 60 inches or more. Rumney fine
sandy loam (Ru) is nearly level with dark grayish surface sands underlain by gray to grayish
brown sand to a depth of 60 inches or more. Adrian mucks are very poorly drained soils of
depressions and lower-order waterways. These mucks typically extend to a depth of 20 inches
and are underlain by fine sands.
1.3.3
Hydrology and Hydraulic Analysis
HEC-RAS output files presenting input and output data for the existing and proposed conditions
are attached in Appendix F for the mean April; May; and August; and 2-, 10-, 50-, 100-year, and
500-year storm events. A summary table of water elevations of select river stations is shown
below in Table 1-8 for the proposed mean August (i.e. low flow) flow conditions. Mean August
was chosen because the greatest relative change in WSE occurs during the lowest flow
conditions. The most extreme change in WSE occurs immediately upstream of the dam with an
elevation drop of 3.64 ft.
Table 1-8 Existing and Proposed Water Elevations, NGVD 29 (Mean August)
Station Description
River Station
Existing
Proposed
Change
(ft)
(ft)
(ft)
(ft)
11,233 ft Upstream of I-95
27812
11.94
11.94
0
TR-35
16240
7.08
6.89
-0.19
TR-34
15802
6.98
6.77
-0.21
TR-33
14964
6.77
6.46
-0.31
TR-32
14090
6.56
6.12
-0.44
TR-31
Immediately Downstream of
Elmwood Avenue
13689
6.51
6.04
-0.47
13440
6.42
5.82
-0.60
TR-30
13330
6.41
5.81
-0.60
TR-29
12540
6.32
5.65
-0.67
TR-28
11752
6.25
5.53
-0.72
TR-27
11158
6.22
5.47
-0.75
TR-26
10795
6.18
5.37
-0.81
TR-25
10457
6.11
5.13
-0.98
TR-24
9932
6.05
4.96
-1.09
TR-23
9206
5.91
4.28
-1.63
TR-22
8720
5.91
4.32
-1.59
TR-21
8216
5.90
4.29
-1.61
TR-20
7732
5.87
4.11
-1.76
TR-19
6991
5.85
4.07
-1.78
TR-18
6426
5.84
4.03
-1.81
TR-17
5840
5.82
3.93
-1.89
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June 2010
Station Description
River Station
Existing
Proposed
Change
(ft)
(ft)
(ft)
(ft)
TR-16
Immediately Downstream of
Warwick Avenue
5537
5.81
3.80
-2.01
5440
5.80
3.75
-2.05
TR-15
5055
5.79
3.68
-2.11
TR-14
4812
5.77
3.61
-2.16
TR-13
4364
5.76
3.55
-2.21
TR-12
4073
5.74
3.44
-2.30
TR-11
3858
5.72
2.97
-2.75
TR-10
3497
5.71
2.85
-2.86
TR-9
3167
5.70
2.77
-2.93
TR-8
2378
5.68
2.55
-3.13
TR-7
2020
5.67
2.43
-3.24
TR-6
1620
5.66
2.34
-3.32
TR-5
1370
5.66
2.29
-3.37
TR-4
1069
5.66
2.19
-3.47
TR-3
750
5.65
2.12
-3.53
TR-2
Immediately Upstream of
Dam
Immediately Downstream
Dam
199
5.64
2.00
-3.64
70
5.64
2.00
-3.64
61
1.96
1.96
0
59 ft Downstream of Dam
2
-1.55
-1.55
0
Fish Passage Assessment
The purpose of the fish passage assessment is to determine if the target fish species can swim
both upstream and downstream under the proposed conditions. The mean April and the mean
August flows were chosen as the regulating flows. April has the highest monthly flow rates and
would result in the highest average monthly velocities. August has the lowest average flows,
which would result in the lowest water elevations for fish passage.
Table 1-9 shows that the target fish species can pass through the proposed conditions for both the
proposed mean August and mean April conditions. The highest velocity is 5.55 ft/s which
occurs 25 ft downstream (River Station 36) of the breached dam during mean April flow under
proposed conditions. This velocity is within range of burst speed for all fish species of concern.
The minimum depth is 1.41 ft which occurs 25 ft downstream of the dam during proposed mean
August flow. This is well within the range of minimum water depth for fish passage of all
species of concern. Refer to Table 1-3 for fish passage requirements.
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June 2010
Table 1-9 Proposed Depths and Velocities after Partial Dam Removal
River Station
Description
Mean April Flow
Mean August Flow
(ft)
Depth (ft)
Velocity
Depth (ft)
Velocity
TR-35
16240
6.02
1.99
3.29
1.43
TR-34
15802
8.52
1.72
5.87
0.9
TR-33
14964
6.52
1.71
3.86
1.29
TR-32
14090
6.64
1.16
3.92
0.71
TR-31
Directly Downstream of
Elmwood Avenue
13689
6.05
1.32
3.34
0.86
13440
5.46
1.23
2.62
1.3
TR-30
13330
6.14
1.29
3.31
0.93
TR-29
12540
9.01
1.50
6.25
0.8
FEMA E
12000
6.98
1.39
4.26
0.8
TR-28
11752
7.42
1.40
4.73
0.76
TR-27
11158
8.21
1.16
5.57
0.61
TR-26
10795
5.11
1.39
2.47
1.34
TR-25
10457
6.31
1.86
3.63
1.16
TR-24
9932
6.29
1.52
3.66
0.93
TR-23
9206
4.91
2.33
2.08
2.71
TR-22
8720
12.17
0.92
9.42
0.41
TR-21
8216
6.68
1.47
3.99
0.9
TR-20
7732
4.33
1.42
1.61
1.48
TR-19
6991
8.32
1.16
5.67
0.53
TR-18
6426
5.64
1.59
3.03
1.01
FEMA C
5940
7.15
1.67
4.6
0.96
TR-17
5840
6.56
2.05
4.03
1.4
TR-16
Directly Downstream of
Warwick Avenue
5537
4.85
1.63
2.3
1.64
5440
5.51
1.45
2.95
1.05
TR-15
5055
7.29
1.57
4.78
0.82
TR-14
4812
6.73
2.12
4.31
1.16
TR-13
4364
7.70
1.33
5.35
0.67
TR-12
4073
5.20
2.31
2.94
1.7
TR-11
3858
4.72
2.87
2.37
2.18
TR-10
3497
7.00
1.74
4.75
0.86
TR-9
3167
6.64
1.54
4.47
0.71
TR-8
2378
6.30
1.45
4.27
0.74
TR-7
2020
5.76
2.11
3.85
1.23
TR-6
1620
7.01
1.96
5.24
1
TR-5
1370
6.09
1.54
4.39
0.72
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June 2010
River Station
Mean April Flow
Mean August Flow
(ft)
Depth (ft)
Velocity
Depth (ft)
Velocity
FEMA A
1300
4.47
2.47
2.84
1.49
TR-4
1069
6.49
1.5
4.99
0.63
TR-3
750
5.15
1.54
3.82
0.69
TR-2
199
7.52
1.54
6.5
0.58
50 ft Upstream of Dam
120
7.21
1.15
6.2
0.42
Directly Upstream of Dam
70
7.20
1.09
6.2
0.45
Directly Downstream of Dam
61
4.48
2.77
3.56
1.49
36
2.05
5.55
1.41
4.24
2
3.62
1.94
2.8
0.85
Description
1.3.4
Sediment Mobility Analysis
As stated in the FS, excluding riverbanks, there is little to no sediment and little fine sand in the
impoundment above the dam. This suggests that most suspended bed material is conveyed over
the dam on a regular basis. Therefore, sediments transported in the system would be carried over
the existing dam rather than settling in the impoundment upstream.
Trap Efficiency
Trap efficiency is a measure of the ability of an impoundment to force settling (i.e. trapping)
sediments, preventing downstream migration. The trap efficiency depends in part on the volume
of the impoundment, the volume of discharge through the impoundment, and, depending on the
circumstance, the size of the particle that is being settled. At dams, where sediments sizes can
vary based on flow rates and upstream watershed conditions, the trap efficiency is estimated as
the ratio of volume of the impoundment to the average annual flow. The volume of the Pawtuxet
Falls impoundment under existing conditions is estimated to be 123.78 acre-feet.
The average annual flow at the PFD (based on the USGS gage and adjusting for the increased
watershed area at the dam) is 399 cfs. The total runoff per year therefore, was estimated to be
288,863 acre-feet. Trap efficiency at the existing dam is negligible. The PFD is not effective at
trapping upstream sediments within the impoundments. This is supported by the fact that a
minimal amount of sediment was observed within the impoundment upstream of the structure
and that the existing bedload is comprised of medium grained sand. The fact that little fine
grained sediment is present suggests it is already carried over the dam under existing conditions.
Therefore, under a partial dam removal scenario, a dramatic increase in the sediment volumes
transported into Pawtuxet Cove is not expected as most of the sediment in the system is already
being passed through the Pawtuxet Falls impoundment.
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Impact of the Partial Dam Removal on Shear Stress Conditions
The main variable affected by the partial removal of the PFD will be the energy slope, which will
increase in the zone of backwater influence of the dam under the proposed conditions. This will
raise the average channel shear stress, as can be seen in the data provided in Appendix G.
Similarly, the potential for sediment transport increases as the energy slope increases. As can be
seen in the HEC-RAS channel shear stress comparison for a 1.5-year frequency flow under
existing and proposed conditions, all average shear stresses computed are in excess of the critical
shear stress for the sampled sediment at that location, with the exception of cross sections 2 and
4. In other words, the LPR sediments are highly mobile under existing conditions. The
proposed action will therefore not significantly change sediment transport in the LPR.
Cross sections exhibiting excess shear for low-flow, low-tide flow conditions are expected to
erode slightly in some locations until they adjust to equilibrium. However, since the shear
stresses calculated are averaged across each river cross section, it can be assumed that the
magnitudes of shear stress in most bank locations is less than the calculated average shear stress.
Moreover, the time in which these conditions are experienced is limited to the low-tide portions
of the flow. As tide elevation increases, the flow velocities, energy slope, and shear stress
decrease. Therefore sediment transport at low-flow conditions is expected to be minor and
temporary, with the potential for deposition of certain sediment sizes to occur at high tide.
An effective means of limiting sediment erosion along banks is surface treatments utilizing
vegetation for stabilization. These practices should be catered specifically to a site to control the
erosion or sedimentation conditions which may occur, dictated by the near-bank shear stress
conditions.
The LPRRP proposes to rely upon wetland plantings as well as natural re-vegetation techniques
to stabilize the bank areas that are expected to mobilize during 1.5-yr storm events. In addition,
the LPRRP propose to dredge approximately 3,500 yd3 of material along river left immediately
upriver from the PFD that could potentially mobilize downriver. This material is likely to
mobilize downstream because of anticipated changes in the channel/thalweg as a result of this
project. Under proposed partial breach conditions, flow will be directed to river right within the
area of the PFD breach, this will in turn force the thalweg northward as the river comes to an
equilibrium approximately 300-ft beind the dam. This channel realignment would mobilize
sediment as some down-cutting occurs. The sediment that would mobilize as part of this project
will be dredged instead so that it does not impact Pawtuxet Cove.
1.3.5
Sediment Exposure Analysis
Public Access Identification
Areas identified as potentially having substantial existing human use are shown in Figure 9.
Areas exhibiting the highest potential levels of human use include residences just west of the
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PFD, within the Rhodes property, Fay Field trail complex, and fields and trails associated with
Belmont Park in Warwick. A Pawtuxet River Public Access Survey was also conducted on 22
September 2009 by the Narragansett Bay Estuary Program and Save the Bay. Results of this
survey can be found in Appendix I.
Direct Contact Exposure Analysis
Based on modeling results discussed in Section 1.3.3, areas to be exposed as a result of the
proposed project during low water levels (i.e. average August flows) are shown in Figures 10
and 11. Table 1-10 shows the horizontal exposure expected at representative transect locations.
The total square footage of the proposed exposure area is not presented in this project narrative
because interpolation between each transect is not appropriate based the spacing of transects (i.e.
2-ft contours can’t be generated between the 500-ft transect spacing).
Table 1-10. Representative Increases in Width of Riverbank Exposure Areas
Predicted Riverbank Exposure
Increase During Mean August Flows
Transect
Left Bank
Right Bank
Width (ft)
TR-4
6
15
TR-7
9.5
17.5
TR-10
3.5
23
TR-18
4.5
6
TR-22
6
2.5
TR-25
5
7.3
TR-27
2
2
TR-29
1
4
TR-30
1.5
1.5
TR-33
2
2.5
TR-35
0.5
0.5
Areas currently exposed during low water levels (i.e. average August flows) that are located
from I-95 downriver to TR-4 will be fully inundated during proposed 1.5-year frequency flow
elevations. In other words, areas currently exposed during low flow will generally continue to
experience a frequent sediment scour/accretion regime. This means that existing scour/accretion
zones will continue after the dam breach has occurred since scour/accretion events generally
occur as a result of sustained high flow events.
The scour/accretion regime will generally remain unchanged west of TR-4, so any proposed
dredging or capping activity in this area would have no long term effect on human exposure to
river sediment as the areas would continue to change over time. The placement of material able
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to withstand a 100-yr event would be the only solution to semi-permanently capping this material
and that option is not favorable to the ecological and anthropogenic uses of the river.
For areas east (downriver) from TR-4, only >1.5 year frequency flows will reach the existing low
flow elevation. The LPRRA proposes to stabilize and prevent public access to these areas
through the planting of dense stands of native thorny vegetation that can withstand brackish
water and will deter entry to the area. Refer to Sheet 8 of the engineering drawings in Appendix
J for the planting plan.
1.4
Description of the Proposed Action
Introduction
The following narrative describes the Proposed Action. The Proposed Action was developed
utilizing the results discussed in Section 1.3, RIDEM OWR avoidance and mitigation
requirements, and precedent set by RIDEM OWM regarding sediment sampling and remediation
in the LPR.
Detailed engineering drawings are provided as Appendix J. Final plans and specifications will
adhere to applicable USDA-NRCS Conservation Practice Standards for Fish Passage
(Conservation Practice Standard No. 396), Channel Stabilization (Conservation Practice
Standard No. 586), Streambank and Shoreline Protection (Conservation Practice Standard No.
580), and Wetland Enhancement (Conservation Practice Standard No. 659). These design
standards are presented in Appendix K.
The Proposed Action seeks to remove the existing dam structure. The work will be conducted in
two phases: Phase 1 will consist of the proposed dredging upstream of the dam and Phase 2 will
consist of the partial dam removal and installation of plantings. Phase 1 dredging will occur in
November 2010 in accordance with confined aquatic disposal (CAD) cell disposal time
restrictions. Phase 2 partial dam removal and plantings will occur during the low-flow period of
1 July through 31 October 2011 in accordance with the Rules and Regulations Governing the
Administration and Enforcement of the Freshwater Wetlands Act. The portion to be removed
extends from the southern sidewall and extends approximately 150 ft to the north. For the area
between the PFD and Rhodes, native plantings will be installed between the existing vegetation
elevation down to the proposed mean April river elevations to discourage public access to these
areas and help stabilize riverbank sediment. Hydraulic dredging of the sandbar along river left is
proposed to prevent the downstream migration of approximately 3,500 yd3 of sediment that will
become mobilize as the channel/thalweg behind the dam migrates to river left.
Property Boundary and Access Considerations
Work at the PFD will be conducted entirely on the dam structure, which is owned in its entirety
by the applicant (the PRA). A detailed deed evaluation of the PFD is included in Appendix C.
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The work areas will be accessed via work barges launched from Rhodes, which is also the
location of the staging and stockpile area, and off of Aborn Street in Pawtuxet Cove downstream
of the dam. A letter of authorization for use of Rhodes as a staging and launch area is provided
as Appendix L.
Proposed Construction Activities
The general sequence of construction will be as follows:
Phase 1:
1)
2)
3)
4)
5)
6)
7)
Install erosion and sedimentation controls (including downstream absorbent boom)
Prepare staging areas at Rhodes
Install access ramp down to existing water line at Rhodes
Launch barges from Rhodes and Aborn Street and set up hydraulic dredge pipe
Dredge sediment upstream of dam and transport to receiving barge
Restore access ramp area and stockpile area
Remove erosion and sediment controls
Phase 2:
1)
2)
3)
4)
5)
6)
7)
8)
Install erosion and sedimentation controls (including downstream absorbent boom)
Prepare staging areas at Rhodes
Install access ramp down to existing water line at Rhodes
Launch barges from Rhodes
Access dam via barge launched from Rhodes
Install temporary water diversion structures upriver from dam removal area
Remove concrete dam section down to appropriate grade
Perform limited rock removal and rock placement to develop appropriate flow field for
fish passage below the dam structure and aesthetics
9) Remove temporary water diversion structures
10) Stockpile dam debris at Rhodes and then remove material offsite
11) Restore access ramp area and stockpile area
12) Remove erosion and sediment controls
13) Install restoration plantings
All final design and construction efforts will comply with NRCS Conservation Practice
Standards as detailed within Appendix K. The following activities are proposed as part of the
construction effort.

Erosion and sediment controls (including an absorbent boom) shall be installed prior to the
initiation of any other construction activities. The contractor shall provide permanent or
temporary pollution control measures to prevent contamination of adjacent streams,
watercourses, bays, ponds, or other areas of water impoundment. The contractor shall cease
any of his operations which will increase pollution during rain events.
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
Removal of approximately 3,500 yd3 of sediment approximately 300 ft upstream of the dam
will occur via hydraulic dredging. The proposed dredging amount include approximately
0.5 ft of additional dredging depth to compensate for any deposition of sediment that may
occur between the dredging in 2010 and partial dam removal in 2011. The dredging barge
will be launched from Rhodes and the receiving barge will be launched off of Aborn Street in
Pawtuxet Cove. The dredged material will be piped to the receiving barge and dewatered on
the barge prior to disposal. Dredged material will be disposed of in a CAD cell located in the
Providence River.

Access to the dam site and proposed bank stabilization areas will be gained via work barge,
which will be launched from Rhodes. The barge is expected to draw up to 2-ft 6-in. when
loaded with 35,000 lbs of equipment and material. Several barge sections may be utilized
(each with the similar capacity and draft). After partial dam removal, the proposed minimum
water depth within the main channel from the dam to Rhodes is expected to be approximately
3.82-ft (in the vicinity of TR-3), which will be sufficient depth for the barge(s).

A series of temporary cofferdam water deflection structures may be placed immediately
upstream of the dam removal area to direct flow over the northern section of the dam during
construction activities. The contractor shall submit shop drawings detailing top elevations,
layout, and the type of cofferdam to the engineer for approval at least 15-days prior to
construction.

Partial dam removal will occur through demolition and removal of approximately 150-ft of
the southern section of the dam. The partial dam removal will occur between the southern
ledge to the center ledge as shown on Sheet 4 in Appendix J. Demolition and removal of the
structure will occur down to bedrock. Limited removal of bedrock will also occur on site
through use of jackhammer or similar device. Approximately 100 yd3 of concrete is
expected to be removed. Concrete will be removed and disposed of an appropriate offsite
facility. Less than 20 yd3 of bedrock excavation is expected and will be utilized as part of the
flow field development and fish resting zones required for fish passage (detailed locations to
be provided after conceptual regulatory approval) at the dam removal site, or for bank
stabilization efforts occurring below proposed April mean flow elevations.

Upon completion of the partial dam removal and associated fish passage restoration activities
within the dam area, the temporary cofferdams will be removed.

Two zones of restoration plantings are proposed on both sides of the river. Zone 1 extends
from the PFD to upstream of TR-5 and will consist of dense stands of native thorny
vegetation that can withstand brackish water and will deter entry to the area. Zone 2 will
consist of dense stands of other native vegetation, thorny and non-thorny, and will extend
from the upper boundary of Zone 1 upstream to Rhodes. Property owners in Zone 2 will be
consulted for the selection of native plants to be installed in this area.
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Erosion and sediment control measures are shown on the project plans and shall include the
following Contractor Requirements:
1) Earthmoving activities in the project area shall be conducted in such a manner as to
prevent accelerated erosion and the resulting sedimentation on the site and abutting
properties.
2) Channels and banks will be stabilized in accordance with NRCS Practice Standard Codes
584 and 580, respectively.
3) The contractor shall, at all times, have on hand the necessary materials and equipment to
provide for early slope stabilization and corrective measures to damaged slopes. The
contractor shall respond to maintenance or additional measures ordered by the engineer
and/or owner within 24 hours.
4) The contractor shall install temporary erosion control structures as necessary to prevent
accelerated erosion and sedimentation prior to initiating work. The erosion control
features shall be checked daily and after each storm event for damage, until such features,
at the opinion of the engineer and/or owner, are no longer needed.
5) All slopes of stockpile material and other disturbed areas shall be stabilized and protected
by surrounding with silt fencing and hay bales, or otherwise protected as approved by the
engineer. Silt fences and staked hay bales shall be installed at the site downgradient of
work areas and as shown on the drawings.
6) Downstream absorbent boom to be installed in accordance with manufacturers
specifications. Contractor shall submit specifications to the engineer for approval prior to
deployment.
7) All temporary erosion control measures will be maintained throughout the course of the
site construction activities, including shutdown periods.
8) At the completion of the project, and after all disturbed areas are stabilized, the contractor
shall completely remove all sedimentation and erosion control measures.
All in-river construction is proposed to occur during the low-flow period, generally between 1
July and 31 October, and all dam material removed will be disposed of in a suitable off-site
location.
Surface boulders, approximately two to three ft in diameter, will be installed to direct flow and
create fish resting zones downstream of the removed dam. A USFWS hydraulic engineer will be
consulted for guidance prior to the placement of the boulders. Similarly sized stone will be
placed in front of the remaining dam structure to improve aesthetic features associated with the
remaining structure. Refer to Table 3-1 in Section 3 for further details on all temporary and
permanent wetland impact areas.
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2. AVOIDANCE AND MITIGATION
2.1
State-Regulated Resource Areas
The following section provides EA’s determination of the presence of State-regulated Freshwater
Wetlands and other resource areas identified in the project area in accordance with RIDEM
regulations.
2.1.1
Freshwater Wetlands
The Pawtuxet River is identified as a perennial “blue-line” watercourse on available USGS
topographic mapping for the Providence Quadrangle. As such, the resource is classified as a
“River” according to the “Rules and Regulations for Governing the Administration and
Enforcement of the Freshwater Wetlands Act” (the Rules). In addition, the River is greater than
10-ft wide and therefore, a 200-ft Riverbank Wetland is applied per the Rules.
The locations of the field-delineated wetlands located within the RCA are shown on Sheet 2 of
the plans in Appendix J. The wetland complexes along the River immediately upstream of the
PFD consist of Forested and Emergent vegetation communities. The emergent components of
these wetlands are less than one acre in area and the forested components are less than three
acres and therefore, the wetland complex does not warrant a 50-foot Perimeter Wetland.
A stream was delineated approximately 1,200 feet upstream of the PFD along river right. This
stream flows northeasterly through a culvert underneath Post Road, adjacent to a warehouse
complex, and into the LPR. Immediately adjacent to Post Road the stream is greater than 10 feet
wide and therefore, a 200-ft Riverbank Wetland is applied in this area. From approximately 25 ft
northeast of Post Road to the river, the stream is less than 10 ft wide and therefore, a 100-ft
Riverbank Wetland is applied.
As discussed in Section 1.2.3, wetlands outside of the RCA will not be directly impacted by
construction and were not field-delineated. The locations of the wetlands in this LTRA were
determined based on RIGIS data and ground-truthing. As a result, setbacks such as Perimeter
and Riverbank Wetlands were not assessed as there will be no impacts to these setback areas as a
result of the project.
As a result of these investigations, the project proponents do not expect the LPRRP to cause
significant changes to wetlands within the LTRA. These wetlands are primarily fed by surface
water from up-gradient sources, particularly storm water from developed areas, and are underlain
by relatively impermeable soils. While the wetlands are periodically flooded by the river, these
are relatively infrequent events and appear to be relatively unimportant to the character of the
wetlands. While such events will become slightly less frequent post-restoration, they will
continue to occur. Conversely, the restoration will restore more natural flooding regimes to the
floodplain wetlands of the LPR while restoring and enhancing wetland functions and values such
as wildlife habitat, flood storage, and recreation.
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Floodplain
According to the Rules, “Flood Plain” is defined as the land area adjacent to a river or other body
of flowing water which is likely to be covered with flood waters resulting from a 100-year
frequency storm. The project area is located entirely within the 100-year freshwater flood plain
as defined by FEMA Flood Insurance Rate Mapping (Figure 12). The Flood Plain generally
occurs up to between elevations 16 and 24 ft NGVD29, and is within a densely populated
suburban area.
2.1.3
Office of Waste Management Regulations
As noted above, the LPRRP proponents undertook intensive review of the extensive sediment
sampling data available for the LPR and Pawtuxet Cove, as well as the administrative record at
RIDEM pertaining to Ciba remediation. Following the 2002 Ciba sampling effort (Ciba, 2003)
RIDEM and EPA determined that no further remediation of the LPR sediments (channel or bank)
was necessary, indicating that the agencies agreed that sediment remediation goals within the
LPR were sufficiently protective of human health and the environment. Additionally, testing
was never required of downstream Ciba legacy sediments that were deposited in areas above
existing mean August flow elevations (i.e. existing exposure areas). Further, as noted in Sections
1.3.4 and 1.3.5 above, the LPR channel and bank sediments are mobile under existing conditions
at 1.5 year flow and above, with scour and deposition actively occurring. Therefore, the
proposed LPRRP action will not significantly change exposure or transport variables. Postrestoration, scour and deposition of sediments will continue to occur as is presently the case.
2.2 Infrastructure
2.2.1 Infrastructure Scour Analysis
Partial removal of the PFD will decrease water levels and increase velocities upstream of the
dam. In order to evaluate the potential for scour at the existing bridges and structures, a channel
shear analysis was conducted to compare the existing conditions to the conditions after partial
dam removal. The five areas of concern are: 1) the Broad Street Bridge, 2) abutment walls in
the vicinity of the dam, 3) Rhodes, 4) Warwick Avenue Bridge, and 5). Elmwood Avenue
Bridge.
The Amtrak Bridge and I-95 Bridge, located approximately 15,330 ft and 16,370 ft upstream of
PFD, respectively, were not analyzed as the proposed partial dam removal would result in an
insignificant change to WSEs and velocities at these locations. A water elevation drop of just
over 1 in. would occur after the partial dam removal at the I-95 Bridge and Amtrak bridge during
the 1.5-year and 2-year frequency flows, according to the hydraulic analysis. Storms with a
frequency of 10-, 50-, 100-year, and 500-year had almost zero change in water elevations and
velocities. The 1.5-year frequency flow is discussed frequently in this section, which is typically
the flow that carries most sediment in a river system. The locations of infrastructure analyzed as
part of this application are presented in Figure 4. RI Department of Transportation will be
apprised of the findings and recommendations.
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2.2.2 Broad Street Bridge
The Broad Street Bridge is located just downstream of the PFD. The bridge’s three spans are
constructed incorporating two large outcroppings or rock ledge. As the dam is a run-of-the-river
structure, the proposed partial dam removal will have no effect on water elevation, water
velocity, and channel shear downstream under proposed conditions. Modifications or
reinforcement of the Broad Street Bridge, therefore, will not be necessary.
2.2.3 Pawtuxet Dam Abutment Walls
The river banks at the PFD are steep and partially vegetated. The south bank consists of a large
concrete retaining wall (which is situated on top of bedrock), bedrock outcrops, and fill material
that contains various forms of urban debris. The south bank retaining wall extends
approximately 15 ft upstream of the dam and then cuts 15 ft into the bank (perpendicular to
flow). During existing mean August flows, the water level is already below the concrete on the
south bank retaining wall and lower water levels associated with partial removal of the adjacent
dam would not affect the structural integrity of the south wall. Vegetation will be planted from
the proposed mean April flow elevation up to the existing vegetation elevation to protect the
bank from the increased velocities that are expected in this area.
The north bank consists of a rubblestone retaining wall that extends from the Broad Street Bridge
west to about 10 feet upstream of the PFD spillway. The north part of the spillway connects to
the north bank wall, but this portion of the spillway will not be removed and the retaining wall
would remain stable despite removal of the southern portion of the PFD. The area in front of the
north bank retaining wall that will become exposed under proposed conditions will be protected
from the existing vegetation elevation down to proposed mean April flow elevations with planted
vegetation.
2.2.4 Rhodes on the Pawtuxet
Rhodes on the Pawtuxet is located approximately 2,200 ft upstream of the PFD. Sediment
samples were taken approximately 175 ft downstream and upstream of the facility (EA Transects
TR-7 and TR-8, respectively) from the banks of the channel that consisted of well graded sand
(TR-7) and poorly graded sand with silt (TR-8). The permissible shear stress for sediment
samples taken at TR-7 and TR-8 is 0.08 and 0.05 lb/ft2, respectively (Appendix G). At the
Rhodes on the Pawtuxet, water level decreases of 1.09 ft are anticipated due to the partial
removal of the PFD during the 1.5-year frequency flow, with negligible increases in shear stress.
The partial removal of the dam will not significantly increase scour along the facilities support
piers, so reinforcement will not be necessary in the vicinity of the piers. Some existing concrete
cracking was observed on several of the piers. There is an existing, though informal and
unimproved, canoe access point on the Rhodes property, immediately upstream (west) of the
building on the north (Cranston) bank of the LPR. Subject to the approval of Rhodes
management, the LPRRP proponents are proposing to improve this access point in order to
ensure that the restoration will not adversely impact recreational access to the river, nor increase
human exposure to river sediments.
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2.2.5 Warwick Avenue Bridge
The Warwick Avenue Bridge is located approximately 5,430 ft upstream of the PFD. Water
levels decrease only 0.41 ft as a result of the partial removal of the PFD during the 1.5-year
frequency flow. The 1.5-year frequency flow under the proposed conditions will result in an
increase of channel shear stress from 0.16 lb/ft2 to 0.18 lb/ft2. This minimal increase in shear
stress is not expected to compromise the Warwick Avenue Bridge as its concrete piers are
protected by a 4 ft deep layer of 8” stone. This size stone has a permissible shear stress greater
than 2.0 lb/ft2. Additionally, each concrete pier has timber piles to support the piers.
2.2.6 Elmwood Avenue Bridge
The Elmwood Avenue Bridge is located approximately 13,400 ft upstream of the PFD. A
sediment sample was taken approximately 150 ft downstream of the bridge (EA Transect TR-31)
from the center of the channel that consisted of well-graded gravel with sand and had a
permissible shear stress of 1.16 lb/ft2 (Appendix G). The Elmwood Avenue Bridge exhibits
water level decreases of only 0.14 ft due to the partial removal of the PFD during the 1.5-year
frequency flow, with negligible increases in shear stress. The partial removal of the dam will not
significantly increase scour along the bridge piers, so reinforcement will not be necessary in the
vicinity of the bridge piers. Additionally, each concrete pier has piles that are driven to a
minimum depth of 20 ft below existing grade. The abutment walls appear to be in good shape
based on inspection, indicating no scour has occurred to date.
2.2.7 Other Structures
The former Conrail bridge located approximately 7,000 ft upstream of the PFD is no longer in
use. Structural information was not obtained for this structure. Also, a pedestrian bridge was
formerly located 200 ft upstream of the non-functioning Conrail bridge. The pedestrian bridge
has been removed and the piers have been left in place. Because these structures have been
abandoned and are inaccessible to the public, they have not been assessed as part of this
narrative.
2.3
Historic and Cultural
The proposed restoration will significantly improve the historic and cultural values of the LPR
by re-establishing natural resource and cultural features which existed from the time of the
Wisconsinian glacial maximum until the 17th century and were highly significant to pre-Anglo
native people of present-day Rhode Island (PAL, 2006). The restoration of the natural riverine
function and historic diadromous fish run will reestablish a natural resource and cultural land-use
at Pawtuxet Falls (Renderings 1 and 2) (PAL, 2006). The PFD is not listed on the National
Register, however, the dam is a contributing element to Rhodes, which is listed on the National
and State Registers of Historic Places and is a National Historic Landmark. NRCS has also
consulted with the Advisory Council on Historic Preservation, which has determined that their
participation in the evaluation of impacts is not necessary. Further review under Section 106 is
ongoing.
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2.4
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Mitigation Measures
To fulfill the Avoidance and Minimization Requirements of Rule 10.02 D. of the Rules, the PRA
must demonstrate that all probable impacts to freshwater wetlands have been avoided or
minimized to the maximum extent possible. In developing the LPRRP, the project proponents
have made every effort to maximize the restoration of wetland functions and values, while
minimizing adverse impacts. During construction, numerous best management practices (BMPs)
will be installed between the limit of work and adjacent wetland resource areas prior to the start
of construction. These BMPs are shown on the engineering drawings (Appendix J), and include
such measures as hay bales, silt fences, absorbent booms, and cofferdams.
Rendering 1. Proposed Partial Breach at Spring Low Tide
(Source: MMI)
Given that the purpose of this project is to restore natural riverine functions which will provide
significant environmental improvement for the entire ecological community within the LPR, no
additional mitigation measures are necessary.
2.4.1
Impact Avoidance
Description of the primary purpose of the project - The purpose of this project is to restore
natural riverine ecology, historic spawning habitat for native migratory fish, wetland functions
and values, and to improve water quality along the lower Pawtuxet River main stem from
Pawtuxet Falls Dam to Pontiac Mills, as well as along the lower Pocasset River and other
tributaries of the LPR. The project provides a foundation for a wide range of ecological
restoration activities along the lower Pawtuxet, including floodplain wetland restoration in the
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Fay Field area of Cranston and additional wetland and fish passage restoration upstream of
Pontiac and along the tributaries.
Whether the primary proposed activity is water-dependent, or whether it requires access to
freshwater wetlands as a central element of its primary purpose – The proposed activity is
water dependent as it involves the modification to features at an existing dam. The proposed
project will restore natural riverine function and diadromous fish passage at the PFD and will
provide a net ecological benefit to water quality, fish and wildlife, and wetland systems within
the project area.
Whether there are areas within the same property or other property owned or controlled by the
applicant that could be used to achieve the same project purpose without altering the natural
character of any freshwater wetlands – The proposed project location is an impediment to
natural river flow and migratory diadromous fish and is therefore the only logical location for the
proposed fish passage restoration project.
Whether any other properties reasonably available to, but not currently owned or controlled
by, the applicant could be used to achieve the project purpose while avoiding wetland
alterations – The proposed project location is an impediment to natural river flow and migratory
diadromous fish and is therefore the only logical location for the proposed fish passage
restoration project.
Whether alternative designs, layouts or technologies could be used to avoid freshwater
wetlands or impacts on functions and values on the subject property or whether the project
purpose could be achieved on other property that is reasonably available and would avoid
wetlands – In developing and designing the LPRRP, project proponents undertook a full
alternatives analysis (Appendix B). The analysis, as well as the professional judgement of
numerous experts in ecological restoration, concluded that the proposed partial removal of PFD
would provide the greatest benefit to the LPR ecosystem.
The No Action Alternative would minimize the potential for wetland change; however, the
project goal of restoring natural riverine functions and native fish habitat would not be realized
and the LPR would continue to suffer ecological harm as a result.
Full dam removal was also considered; however it would not provide optimal fish passage under
all flow conditions and, therefore, would not provide the same degree of habitat and ecological
benefits as the proposed action.
Construction of a fish ladder would not change the hydraulics of the river system and would limit
wetland impacts to those associated with construction. However, the ladder option would allow
passage of fewer fish species than the proposed action and would not improve water quality or
restore natural river flow and processes; therefore it would not provide the same degree of
ecological benefit as the proposed action.
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Installation of a rock ramp would maintain the existing WSE in the impoundment and potentially
limit wetland impacts. However, a ramp at this location was determined to be impracticable with
respect to engineering and construction, and would also fail to improve water quality or restore
natural river processes.
Whether the applicant has made any attempts (and if so what they were) to avoid alterations to
freshwater wetlands by overcoming or removing constraints imposed by zoning,
infrastructure, parcel size or the like – The LPRRP will significantly improve wetland functions
and values along the LPR by improving biological connectivity and restoring natural riverine
processes. Regarding construction impacts, this project has been designed to occupy the smallest
practicable footprint. There are no constraints to be overcome related to zoning or parcel size
that would avoid wetland alterations.
Whether feasible alternatives that would not alter the natural character of any freshwater
wetlands on the subject property or on property that is reasonably available, if incorporated
into the proposed project, would adversely affect public health, safety or the environment –
The LPRRP will significantly improve wetland functions and values along the LPR by
improving biological connectivity and restoring natural riverine processes. There are no feasible
alternatives (described above) that would achieve the project’s goal of restoring natural riverine
function and providing diadromous fish passage that would not alter the existing character of any
freshwater wetlands.
2.4.2
Impact Minimization
Whether the proposed project is necessary at the proposed scale or whether the scale of the
wetland alteration could be reduced and still achieve the project purpose – The LPRRP will
significantly improve wetland functions and values along the LPR by improving biological
connectivity and restoring natural riverine processes. The proposed project is necessary at the
proposed scale in order to restore natural riverine function and diadromous fish passage.
Whether the proposed project is necessary at the proposed location or whether another
location within the site could achieve the project purpose while resulting in less impact to the
wetland – Pawtuxet Falls Dam is an impediment to migratory diadromous fish and is actively
harming the environmental quality of the Pawtuxet River. The proposed location is therefore the
only logical location for the proposed project.
Whether there are feasible alternative designs, layouts, densities, or technologies that would
result in less impact to the wetland while still achieving the project purpose – Dam removal is a
well established technology which has been used with success nationwide to accomplish river
restoration objectives. The proposed design utilizes a proven technology to achieve the objective
of restoring fish passage while avoiding and minimizing adverse wetland impacts.
Whether reduction in the scale or relocation of the proposed project to minimize impact to the
wetland would result in adverse consequences to public health, safety, or the environment –
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No significant adverse consequences to public health and safety and/or the environment are
anticipated.
2.4.3
Additional Review Criteria for Application to Alter
Review Criteria 1: The proposed project will not result in significant alteration in the overall
wildlife production or diversity of a wetland. – The proposed project will have significant
positive effects on wildlife production and diversity in the LPR main stem and adjacent
wetlands. PFD is actively harming the wildlife production and diversity of habitat, by preventing
native migratory fish from reaching their historic spawning areas. Where fish passage is
unobstructed, anadromous fish such as river herring and shad are highly productive in systems
such as the Pawtuxet. Further, they provide significant ancillary benefits by providing forage for
pisciverous fish, birds, reptiles and mammals in fresh and salt water systems. The LPRRP will
significantly improve the productivity and diversity of wetlands in the LPR and Narragansett
Bay, including everything from ospreys and herons, to otter and mink, to striped bass and
bluefish. Other net ecological benefits associated with the proposed project include:






Increase in species richness (diadromous fish, small mammals, macroinvertebrates)
Improved wildlife corridor
Increased dissolved oxygen within the river
Decrease in seasonal water temperatures
Improved biological connectivity
Decrease in invasive species
Review Criteria 2: The proposed project will not result in significant reduction in the ability of
a wetland to satisfy the needs of a particular wildlife species. – As stated in the response to
Review Criteria 1, the proposed project will result in an increase in species richness, improved
wildlife corridor habitat, and a decrease in invasive species. The proposed project will not result
in a reduction in the ability of a wetland to satisfy the needs of a particular wildlife species. As
stated in Section 3.2.3, removing the dam and lowering the impoundment will reduce the
frequency of storm flows inundating upstream wetlands. It is unlikely that wetland cover types
(forested versus scrub-shrub or emergent) or wetland functions and values would change
substantially with the partial dam removal scenario. In addition, other controlling hydrologic
controls for these wetlands (i.e. upgradient surface water inputs) will not be affected.
Review Criteria 3: The proposed project will not result in significant displacement or
extirpation of any wildlife species from a wetland or surrounding areas due to the alteration of
the wetland. – Noise associated with construction may temporarily affect bird species utilizing
the area. However, any displaced bird species will likely return following the completion of the
project. In addition, the temporary noise impacts will generally occur in urbanized areas. With
the exception of temporary noise impacts, no displacement or extirpation of any wildlife species
is expected to result from the proposed project.
Review Criteria 4: The proposed project will not result in any reduction in the ability of the
wetland to ensure the long-term viability of any rare animal or rare plant species. – According
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to RIGIS data provided by RIDEM, in conjunction with the Rhode Island Natural Heritage
Program, there are no known rare species in the vicinity of the project area. Regardless, the
proposed project will not result in any reduction in the ability of on-site wetlands to ensure the
long-term viability of any rare species. As stated in Response to Review Criteria 1, the proposed
project will result in an increase in species richness, improved wildlife corridor habitat, and a
decrease in invasive species.
The project will have a positive effect on diadromous fish species, which are listed by RIDEM as
species of Greatest Conservation Need as defined under the State Wildlife Conservation Plan.
Review Criteria 5: The proposed project will not result in any degradation in the natural
characteristic(s) of any rare wetland type. – There are no rare wetland types in the vicinity of
the proposed project or within the limit of proposed work. As such, the proposed project will not
result in any impact to the natural characteristic(s) of any rare wetland type.
Review Criteria 6: The proposed project will not result in significant reduction in the
suitability of any wetland for use by resident, migratory, seasonal, transient, facultative, or
obligate wildlife species, in either the short- or long-term as a travel corridor; feeding site;
resting site; escape cover; seasonal breeding or spawning area. – The proposed project will
improve the suitability of the LPR wetlands for use by resident, migratory, seasonal, transient,
facultative, and obligate wildlife species, over short and long terms as a travel corridor; feeding
site; resting site; escape cover; seasonal breeding or spawning area. Specifically, the proposed
project will restore approximately 10 river miles of historic diadromous fish habitat, as well as
other migratory and resident species. This area will serve as important breeding and rearing
habitat for diadromous fish. In addition, the proposed project will result in the increase in
diadromous fish use within this portion of the Pawtuxet, potentially promoting an increase in
piscivorous birds and fish such as striped bass within Narragansett Bay. As mentioned in the
response to Review Criteria 3, noise associated with construction may temporarily affect bird
species utilizing the area, however, any displaced bird species will likely return following the
completion of the project.
Review Criteria 7: The proposed project will not result in any more than a minimal intrusion
of, or increase in, less valuable, invasive, or exotic plant or animal species in a wetland. – The
proposed project is not expected to result in the increase of any invasive, or exotic plant or
animal species in the wetlands along the Pawtuxet River.
Review Criteria 8: The proposed project will not result in significant reduction in the wildlife
habitat functions and values of any wetland which could disrupt the management program for
any game or non-game wildlife species carried out by state or federal fish, game, or wildlife
agencies. – The proposed project will not result in significant reduction in the wildlife habitat
functions and values of any wetland, and will in fact significantly support the management of
game and non-game wildlife species by state and federal fish and wildlife agencies. Specifically,
the LPRRP will support RIDEM’s goal of restoring anadromous fish, as set forth in the agency’s
Wildlife Conservation Strategy as well as its Strategic Plan for the Restoration of Anadromous
Fishes, and will also support objectives of the National Marine Fisheries Service and U.S. Fish
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and Wildlife Service. All of these agencies have been active partners in designing and funding
the LPRRP.
Review Criteria 9: The proposed project will not result in significant reduction in overall
current or potential ability of a wetland to provide active or passive recreational activities to
the public. – The proposed project will improve recreational activities, such as canoeing and
kayaking, by allowing more connectivity to other water bodies adjacent to the Pawtuxet
River. Proposed water depths are more than sufficient to continue to provide recreational
opportunities on the river. As noted above, the project proponents intend to work with Rhodes
on the Pawtuxet to enhance the existing but informal and unimproved canoe access on that
private parcel.
Review Criteria 10: The proposed project will not result in significant disruption of any ongoing scientific studies or observations. – To the best of the Applicant’s knowledge, there are no
on-going scientific studies or observations occurring in the project area.
Review Criteria 11: The proposed project will not result in elimination of, or severe limitation
to traditional human access to, along the bank of, up or down, or through any rivers, streams,
ponds, or other freshwater wetlands. – The proposed project will not result in the elimination or
limitation of traditional human access of any kind. As noted above, the project proponents
intend to work with Rhodes on the Pawtuxet to enhance the existing but informal and
unimproved canoe access on that private parcel.
Review Criteria 12: The proposed project will not result in any reduction in water quality
functions and values or negative impacts to natural water quality characteristics, either in the
short- or long-term, by modifying or changing: water elevations, temperature regimes,
volumes, velocities or flow regimes of water; increasing turbidity; decreasing oxygen; causing
any form of pollution; or modifying the amount of flow of nutrients so as to negatively impact
wetland functions and values. – The proposed project is expected to actually improve water
quality functions and values and will have positive impacts to natural water quality
characteristics, in both short- and long-term. The positive effects of dam removal on water
quality are well documented (e.g., The Ecology of Dam Removal by American Rivers). By
restoring natural velocity and residence time to the LPR, and by restoring natural channel width,
the LPRRP is expected to reduce water temperature and improve dissolved oxygen, with positive
effects on water quality and habitats in the LPR and Narragansett Bay. Moreover, by reducing
residence time and stream temperature, the LPRRP is likely to reduce bacterial production in the
LPR—which has negative impacts on shellfish beds in Narragansett Bay—and nuisance algae
production, which has been a cause of concern for residents of Pawtuxet Village. On the
Cuyahoga River in Ohio, the Kent Dam was removed specifically to restore water quality,
leading to expected de-listing of the river reach under CWA Sxn. 303d. As noted above,
sediment transport conditions post-removal of PFD are expected to be similar to current
conditions. Sediment control measures will be employed as appropriate to prevent turbidity and
sedimentation resulting from construction activities.
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This project is an important step towards achieving improved water quality and general
ecological health improvements in the LPR and Narragansett Bay.
Review Criteria 13: The proposed project will not result in any placement of any matter or
material beneath surface water elevations or erection of any barriers within any ponds or
flowing water bodies of water which could cause any hazards to safety. – The primary objective
of this project is to remove, rather than place, material in the Lower Pawtuxet River. That said,
some manipulation of bedrock below the falls may be necessary to ensure sufficient depth of fish
passage, and pending determination of SHPO, the project partners may add stone facing to the
remnant PFD spillway. None of this placement will, however, cause any hazards to safety,
whether by altering flooding characteristics or by presenting hazards to navigation. In fact, the
proposed restoration will improve public safety by eliminating an extremely dangerous situation
which now exists at PFD under high-flow conditions. Nationwide, hundreds of people have been
killed by drowning beneath the spillways of similar low-head dams, and in the case of PFD, the
steep north bank is extremely hazardous under wet conditions. By redirecting flow to the south
side of the river, the LPRRP will significantly improve public safety at PFD during most flow
situations.
Review Criteria 14: The proposed project will not result in significant loss of open space or
significant modification of any uncommon geologic or archaeological features. – No
uncommon geologic or archaeological features occur in the project area and as such, no loss or
modifications to these features will occur. No loss in the open space that occurs along the river
corridor will occur as a result of the proposed project. Section 106 consultation is ongoing for
this project. See Appendix M for additional information on the draft MOA.
Review Criteria 15: The proposed project will not result in significant modification to the
natural characteristics of any wetland area of unusually high visual quality. – The proposed
project will not result in significant modification to the natural characteristics of any wetland
area of unusually high visual quality. The wetlands along the LPR, while ecologically valuable,
are not of unusually high visual quality; and in any event, will not be significantly modified by
the LPRRP, as detailed herein.
Review Criteria 16: The proposed project will not result in any decrease in the flood storage
capacity of any freshwater wetland which could impair the wetland’s ability to protect life or
property from flooding of flood flows. – The proposed project will not result in any decrease in
the flood storage capacity of any freshwater wetland which could impair the wetland’s ability to
protect life or property from flooding of flood flows. Pawtuxet Falls Dam is a “run-of-river”
dam, meaning that the impoundment itself stores no water. During flood events, the wetlands
adjacent to the river do store floodwaters which are slowly released to the channel via surface
connections. According to HEC-RAS modeling performed for the project, surface water
elevations upstream of the dam will decrease with partial removal of the dam. Downstream of
the existing dam, WSEs will not change. Since any proposed change in WSE is a decrease, the
change in WSEs for proposed conditions were determined to have no negative impacts on
existing flood storage capacity. This project will not impair the wetland’s ability to protect life
or property from flooding or flood flows. The project is expected to improve flood storage
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capacity within the LPR and is expected to reduce flood impacts on life and property upstream of
PFD.
Review Criteria 17: The proposed project will not result in significant reduction of the rate at
which flood water is stored by freshwater wetland during any flood event. – As discussed in
detail in Section 3.2.3, the partial removal of the dam may reduce the frequency of storm flows
inundating some of the wetlands in the project area. As shown in Figures 13 through 16, the
majority of the wetlands directly adjacent to the LPR are inundated only by the 1.5-yr frequency
flow and the less frequent flow events under existing conditions. While the frequency of the
flooding may decrease, these wetlands will continue to be inundated by storm events and will
maintain the same capacity to store flood waters at the same rate as before.
Review Criteria 18: The proposed project will not result in restriction or significant
modification of the path or velocities of flood flows for the 2-year, 10-year, 25-year, or 100year frequency, 24-hour, Type III storm events so as to cause harm to life, property, or other
functions and values provided by freshwater wetlands. – According to HEC-RAS modeling
performed for the hydraulic analysis, surface water elevations upstream of the dam will decrease
with partial removal of the dam. Downstream of the existing dam, WSEs will not change. Since
any change in WSE is a decrease, the change in WSEs for proposed conditions were determined
to have no negative impacts on existing flood storage capacity. As a result, no restriction or
significant modification of the path or velocities of flood flows will occur. The project is
expected to improve flood storage capacity within the LPR and is expected to reduce flood
impacts on life and property upstream of PFD.
Review Criteria 19: The proposed project will not result in placement of any structure or
obstruction within a floodway so as to cause harm to life, property, or other functions and
values provided by freshwater wetlands. – Please refer to Response to Review Criteria 13. The
LPRRP will enhance protection of life and property while restoring and improving the natural
functions and values provided by freshwater wetlands.
Review Criteria 20: The proposed project will not result in any increase in run-off rates over
pre-project levels or any increase in receiving water/wetlands peak flood elevations for the 2year, 10-year, 25-year, or 100-year frequency, 24-hour, Type III storm events which could
impair the wetland’s ability to protect life or property from flooding or flood flows. – The
project will not increase run-off rates; in fact it may improve retention times for the many
stormwater flows running into the wetlands of the LPR. It will not increase any peak flood
elevations and will in fact reduce flood elevations under some circumstances by restoring natural
WSE’s to the LPR, and is expected to reduce flood impacts on life and property upstream of
PFD.
Review Criteria 21: The proposed project will not result in any increase in run-off volumes
and discharge rates which could, in any way, exacerbate flooding conditions in flood-prone
areas. – There will be no increase in run-off volumes or discharge rates as a result of the
proposed project. See previous item.
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Review Criteria 22: The proposed project will not result in significant changes in the
quantities and flow rates of surface or groundwater to or from isolated wetlands (e.g. those
wetlands without inflow or outflow channels). – There are no readily identifiable isolated
wetlands within the project area. Generally speaking, however, the palustrine and riverine
wetlands of the LPR will continue to be watered by the sources which are present under existing
conditions, including groundwater, stormwater, and perennial and intermittent watercourses.
Review Criteria 23: The proposed project will not result in placement of any structural best
management practices within wetlands, or proposal to utilize wetlands as a detention or
retention facility. – Temporary erosion and sediment control BMPs (i.e., hay bales, silt fencing,
absorbent booms, and possibly cofferdams) will be installed prior to the start of construction.
During bank grading and restoration, hay bales and silt fences will be installed at the limit of
work. Following the completion of construction all erosion and sediment controls will be
removed. There are no permanent structural BMPs proposed as part of this project and no
wetlands will be utilized as a detention or retention facility.
Review Criteria 24: The proposed project will not result in any more than a short-term
decrease in surface water or groundwater elevations within any wetland. – As discussed in
Section 3.2.3, the partial removal of the dam may reduce the frequency of storm flows
inundating some of the wetlands in the project area. While the frequency of inundation may be
reduced, these wetlands will continue to be inundated by storms events. In addition, other
sources, such as groundwater seeps, drainage outfalls, and permanent and intermittent streams
will continue to flow into the wetlands. By lowering the average surface water elevation within
the river, there will be an associated lowering of groundwater levels directly adjacent to the river.
In the absence of groundwater elevation data at each of the wetlands within the project area, the
Applicant evaluated the frequency of inundation from surface water (see Section 1.3.2.3 and
3.2.3) to determine impacts resulting from the Proposed Action. Changes to wetlands resultant
from the Proposed Action are expected to be minimal and substantially offset by the multitude of
environmental benefits associated with this project. We note that, based on the analysis of
wetland soils provided in Appendix B, the wetlands of the LPR were present long before
construction of PFD. We conclude therefore, that restoration of historic WSE’s to the LPR
channel will restore these wetlands to historic conditions, while improving their functions and
values.
Review Criteria 25: The proposed project will not result in non-compliance with the Rhode
Island Department of Environmental Management Water Quality Regulations. – The proposed
project will not result in reduction in water quality functions and values or negative impacts to
natural water quality characteristics. As stated in Section 1.3.3, water levels in the LPR will be
lowered, and flow velocities will increase under proposed conditions as a result of partial dam
removal. These changes, however, will not result in significant changes in river characteristics,
such as sediment transport, under existing versus proposed conditions. As a result, negative
impacts in water quality functions and values are not anticipated. Moreover, as noted above the
project is expected to significantly improve water quality in the LPR.
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The project was designed to comply with RIDEM Water Quality Regulations. Refer to
Response to Review Criteria 12 for details on proposed erosion and sediment controls, and
BMPs.
Review Criteria 26: The proposed project will not result in any detrimental modification of the
wetland’s ability to retain or remove nutrients or act as a natural pollution filter. – Based on
the hydraulic control points of each of the wetlands as determined by the FS and based on
information provided by NOAA and the HEC-RAS modeling for the partial dam removal,
wetlands in the project area are not expected to be adversely impacted based on changes in
surface flow. As discussed in Section 3.2.3, the partial removal of the dam may reduce the
frequency of storm flows inundating some of the wetlands in the project area. While the
frequency of inundation may be reduced, these wetlands will continue to be inundated by storms
events. Other surface water sources, such as drainage outfalls and intermittent streams, will not
be impacted by the proposed project and the wetlands’ ability to provide floodwater alteration,
nutrient removal, toxicant retention, sediment retention, and wildlife habitat will be maintained
over the long term.
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3. EVALUATION OF FUNCTIONS, VALUES, AND IMPACTS
3.1 Impacts
3.1.1 Dam Structure and Hydraulic Function
The Proposed Action will remove the PFD in order to restore native river ecology, migratory fish
habitat, and natural wetlands functions and values. Although the dam is currently listed as a low
hazard dam, there is no provision for its maintenance, and its condition will continue to
deteriorate over time. The Proposed Action will remove the dam, thereby preventing the
potential failure of the dam and corresponding uncontrolled release of sediments, damage to
adjacent property, and hazard to human life.
Little to no impacts to the adjacent floodplain are expected. HEC-RAS modeling of PFD, as
well as past experience with similar dam removal projects nationwide, indicates that no change
in surface water elevation will occur downstream of the dam. In addition, modeling of all flow
events indicates that the Proposed Action will cause a decrease in upstream water elevation of no
more than 3.64 ft (which occurs during low flow conditions). Since any change in upstream
WSE is a decrease, the change in WSEs for the Proposed Action will have no negative impact on
existing flood storage capacity.
Since the PFD is a run-of-the-river dam, the Proposed Action will have no effect on the quantity
of water within the Pawtuxet River, therefore there will be no impacts to Aquatic Base Flow
(ABF). The PFD will no longer pose an impediment to fish and wildlife passage and will restore
stream/habitat connectivity improving habitat for a wide variety of native fish and wildlife,
including wetland, terrestrial and aquatic birds, fish, mammals, and reptiles.
3.1.2
Geology and Soils
The Proposed Action will not have adverse effects on local geology and soils. The partial
removal of the PFD will have no impact to geological resources or bedrock. Sediment profiles
upstream of the dam will likely change as a result of increased channel velocities. As necessary,
the banks of the river will be stabilized and vegetated in the RCA to protect these areas from
erosion.
3.1.3
Wetland Resources
A total of 77,754 ft2 of River will be directly impacted under the Proposed Action. These
permanent impacts include partial dam removal, dredging, and excavation activities. In addition,
1,480 ft2 of Riverbank Wetland will be permanently impacted as a result of grading activities at
the Rhodes parking lot.
A total of 45,522 ft2 of temporary River and 94,175 ft2 of temporary Riverbank Wetland impacts
will occur as a result of construction activities. These impacts will be temporary in nature and
the areas will be restored following construction. In addition, 41,424 ft2 of restoration planting
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of native vegetation will occur in palustrine wetlands. Refer to Table 3-1 for a summary of
wetland impacts.
Table 3-1 Wetland Impacts
Project Component
Partial Dam Removal/Fish Passage
Dredging
Total Permanent River Impacts:
Total Temporary River Impacts
Impacts
1,750ft2
76,004 ft2
77,754 ft
45,522
As shown in the results of the HEC-RAS model developed for this project (Appendix F), river
water levels during low-flow (i.e. mean August) periods will be reduced by approximately 3 to
3.6 feet in the RCA (Figure 17). Field-delineations and site visits to this area revealed that high
river flows periodically inundate these wetlands during storm events. Indicators included wrack
piles, water lines, and sediment deposits.
Cross-sections were prepared using 2-ft interval topographic data obtained from the City of
Cranston, river bathymetry collected by EA, water level data generated with a HEC-RAS model,
and the spatial location of the wetlands adjacent to the river to determine the frequency that these
wetlands are inundated and the relative importance of these flood flows to the wetlands (Figures
13 through 16). As shown on Figure 13, the forested wetland/emergent marsh wetland
complexes between the dam and Rhodes are generally inundated by the 1.5-yr frequency flow
and greater flows under existing conditions. Under proposed conditions, these wetlands will
continue to be inundated by the 1.5-yr frequency flow; however, the magnitude of flooding may
be reduced. By removing the dam and reducing the WSE, the frequency of storm flows
inundating these wetlands will be similar but the magnitude will be reduced. New vegetated
wetlands may form in the newly exposed areas during low-flow under proposed conditions,
while portions of the existing wetlands along the upland edge may revert to a drier water regime.
It is not expected, however, that wetland cover types (forested versus scrub-shrub or emergent)
or wetland functions and values would change substantially with the partial dam removal
scenario. In addition, other hydrologic inputs such as groundwater seeps, drainage outfalls, and
permanent and intermittent streams will not be affected by this project.
By lowering the average surface water elevation within the river, there may be an associated
lowering of groundwater levels directly adjacent to the river. In the absence of groundwater
elevation data at each of the wetlands within the project area, the Applicant evaluated the
frequency of inundation from surface water (see Section 1.3.2.3 and 3.2.3) to determine impacts
resulting from the Proposed Action. Changes to wetlands resultant from the Proposed Action are
expected to be minimal and substantially offset by the multitude of environmental benefits
associated with this project.
River water levels adjacent to the Fay Field wetland complex will be lowered by approximately
2.75 to 3 feet as a result of removing the dam (Figure 18). Field-delineations and site visits to
this area also revealed that high river flows periodically inundate these wetlands during storm
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events. The cross-sections prepared for this area indicated that this broad wetland complex is
inundated by the 1.5-yr frequency flow and above under existing conditions and will remain
unchanged under proposed conditions. By removing the dam and lowering the river water
levels, the frequency of storm flows inundating these wetlands will be similar, while the
magnitude of flooding may decrease. Despite this change it is not expected that wetland cover
types (forested versus scrub-shrub or emergent) would change substantially with the partial dam
removal scenario, while wetlands functions and values will be significantly improved by the
project. Seasonal backwater depths could be made shallower resulting in emergent species
compositional changes, but the areal extent of open water is not expected to substantially change
in this broad backwater wetland. The proposed project will reduce the frequency of property
flooding upstream of PFD and will reduce the frequency of nuisance flooding of the Fay Field
baseball fields, thereby enhancing the recreational value of these wetlands. Refer to the NOAA
report (Appendix B) for further information on this area.
Further upstream in the LTRA, the modeled reduction in WSE that will result from removing the
dam gradually decrease from approximately 2 feet at Warwick Avenue to approximately one
inch at I-95 during low flow (Figure 18). The wetlands along this reach primarily consist of
forested and scrub-shrub wetlands that are infrequently inundated by river water (Figures 14
through 16). Numerous groundwater seeps, drainage outfalls, and intermittent streams were
observed in these wetlands and appear to have a more significant hydrologic influence than the
infrequent flooding by the river. As such, removing the dam and lowering the river water levels
is not anticipated to impact these wetlands.
3.1.4 Wetland Functions, Values, and Impacts
Based on observations of the dam and adjacent wetlands made during field visits between
February and May 2009, this section assesses six functions and values described in Section 10.02
E. of the Rules. Information provided in the FS was also used to assess wetland functions,
values, and impacts. Refer to Section 1.2.1 for qualifications of individuals associated with the
project.
The functions and values assessed included:
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Wildlife and Wildlife Habitat
Recreation and aesthetics
Flood Protection
Groundwater and Surface Water Supplies
Water Quality
Soil Erosion and Sediment Control
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3.1.4.1 Wetland and Wildlife Habitat
Wetland Characteristics
The project site is within the Pawtuxet River, a perennial river that drains a watershed of
228 mi2. The river is the third largest tributary to Narragansett Bay, with a mean annual April
discharge of approximately 684 cfs. The LPR, which includes the project area, has a very low
gradient with a channel bed slope of approximately 4.6 feet per mile (0.09%). The river
discharges into the tidal waters of Pawtuxet Cove and Narragansett Bay in Pawtuxet Village at
the boundary of Cranston and Warwick.
Within the Long Term Restoration Area (LTRA) of the project, there are extensive palustrine
wetland resources associated with the LPR. According to data obtained from the RIGIS
database, as well as field investigations performed for this project, the majority of wetlands
throughout the project area consist of the Pawtuxet River and its associated floodplain wetlands
which consist primarily of deciduous forested swamps (Refer to Figure 3). The largest wetland
system in the project area is the complex located to the northwest of the Rhodes, adjacent to Fay
Field. This complex consists of forested, emergent marsh, scrub-shrub, and open water wetland
cover types. Some of the wetlands in the Fay Field complex appear to be relict river channels or
oxbows. Other wetlands along the project reach include palustrine open water, emergent marsh,
and scrub-shrub swamp. Most of these wetlands occur on floodplains which appear to receive
surface water inputs only during flood events and which otherwise are hydrologically fed by
shallow groundwater, stormwater outfalls, or small streams.
Hydric soils mapped within these wetlands include Ridgebury, Whitman, and Leicester
extremely stony fine sandy loam (Rf), Rumney fine sandy loam (Ru), and Adrian mucks (Aa)
(Rector, 1981). Ridgebury stony fine sandy loam is nearly level, poorly to very poorly drained
soils along waterways and depressions. The surface layer is typically black, fine sandy loam with
underlying grayish-brown to brown fine sands to a depth of 60 inches or more. Rumney fine
sandy loam (Ru) is nearly level with dark grayish surface sands underlain by gray to grayish
brown sand to a depth of 60 inches or more. Adrian mucks are very poorly drained soils of
depressions and lower-order waterways. These mucks typically extend to a depth of 20 inches
and are underlain by fine sands. These historic wetland soils indicate that the majority of the
LPR wetlands were present long before construction of PFD, and are therefore expected to
persist and flourish post-restoration.
Wildlife Indicators
Common wildlife species in the project area include the white-tailed deer (Odocoileus
virginianus), gray and red squirrels (Sciurus carolinensis and Tamiasciurus hudsonicus,
respectively), white-footed mouse (Peromyscus leucopus), raccoon (Procyon lotor), opossum
(Didelphis virginiana), and an assortment of resident and migratory birds.
A large percentage of the watershed’s mammals, amphibians, reptiles, and birds depend on
wetland or riparian habitat. Common amphibians are red-backed salamander (Plethodon
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cinereus), American toad (Bufo americanus), green frog (Lithobates clamitans), pickerel frog
(Lithobates palustris), gray tree frog (Hyla versicolor), and spring peeper (Pseudacris crucifer).
Reptiles include snapping turtle (Chelydra serpentina), painted turtle (Chrysemys picta), and
common garter snakes (Thamnophis sirtalis). All of these species are expected to persist and
flourish post-restoration.
The proposed project will greatly increase the wildlife diversity of the subject wetlands by
restoring historic migratory fish habitat to the Lower Pawtuxet River, including alewife (Alosa
pseudoharengus), blueback herring (A. aestivalis), American shad (A. sapidissima), and
American eel (Anguilla rostrata). The LPR is identified by RIDEM as a priority site for this
work in its 2002 report, “Strategic Plan for the Restoration of Anadromous Fishes to Rhode
Island Coastal Streams.”
By restoring historic biological connectivity, improving water quality and restoring natural
flooding regimes, the LPRRP will significantly restore and enhance wildlife resources of the
Lower Pawtuxet River.
Wetland Values
Wetlands in the vicinity of the project area provide a number of functions and values to wildlife.
The river system and its associated wetlands serve as a greenway in a heavily-urbanized area.
The river is likely an important travel corridor for non-game bird species, as it provides some of
the few contiguous habitat patches within the Cities of Warwick and Cranston. The river has the
potential to support a substantial run of diadromous fish. The proposed project will restore 10
linear miles of upstream diadromous fish habitat. This area would serve as important breeding
and rearing habitat for diadromous fish.
Proposed Impacts
The proposed project will significantly improve wildlife functions and values of wetlands within
the LPR by restoring historic biological connectivity, improving water quality, restoring natural
flooding regimes, and restoring historic habitat functions, specifically spawning habitat for
native migratory fish. Construction may have limited short-term impacts to wildlife species in
the RCA only. Noise associated with construction may temporarily affect bird species utilizing
the area. However, this impact will be limited to highly urbanized and presently noisy areas of
Pawtuxet Village and any displaced bird species will likely return following the completion of
the project. As discussed in Section 3.2.3, partial removal of the PFD will not significantly
affect wetlands adjacent to the river or change the cover types or functions and values of these
wetlands. According to RIGIS data provided by the RIDEM, in conjunction with the Rhode
Island Natural Heritage Program, there are no known rare species in the vicinity of the project
area. The proposed project will result in the increase in diadromous fish use within this portion
of the Pawtuxet, promoting an increase in piscivorous birds and fish such as striped bass
(Morone saxatilis). The proposed project will result in an increase in wildlife usage at the site.
Net ecological benefits associated with the proposed project include:
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Increase in species richness and diversity (diadromous fish, freshwater fish, small
mammals, predatory birds, macroinvertebrates)
Improved wildlife corridor
Increased dissolved oxygen within the river
3.1.4.2 Recreation and Aesthetics
Wetland Characteristics
The physical characteristics of the wetlands were described previously. A number of recreation
and public access points exist in the project area, including Rhodes and Fay Field Reservation.
Boat launches exist in the project area and boating (canoes and kayaks) is common in the area
above the dam. Water levels resultant from implementation of the Proposed Action will be
adequate for continued recreational usage. As noted above, the project proponents are working
with Rhodes on the Pawtuxet to improve recreational boating access along the main stem
Pawtuxet. Moreover, by reducing the frequency of nuisance flooding of the Fay Field baseball
fields, the LPRRP will enhance the recreational value of these wetlands.
Wetland Values
The wetlands associated with the project area have recreational and aesthetic value in an
otherwise urban area. Recreational activities associated with the project area include passive
activities such as birding and viewing the river, and active activities such as boating and hiking.
This portion of the LPR also has aesthetic value, as it is a prominent greenway along the
Cranston and Warwick border.
The project area has the potential to provide improved recreational functions. Partial removal of
the dam will increase spawning habitat and populations of diadromous fish, thereby increasing
recreational fishing opportunities in the LPR as well as Narragansett Bay. In addition, the
project area has the potential to be utilized for educational opportunities for local schools
following the partial removal of the dam. The project area would make an effective setting for
environmental and cultural education.
Proposed Impacts
The proposed project will have short-term impacts to recreation and aesthetics. Access to the
RCA will be restricted to the public during construction, limiting any recreational activities.
Upon completion, the project is likely to improve recreational use by improving the boating
corridor, improving canoe access and reducing flood impediments to baseball games. Canoe
launches along the LPR in both the Cities of Cranston and Warwick will allow recreational
boaters the opportunity to navigate the Pawtuxet River from Pawtuxet Cove to the Pontiac Mills
Dam.
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3.1.4.3 Flood Protection
Drainage Characteristics
The Pawtuxet River drains a 228 mi2 watershed consisting mainly of urbanized high density
residential, commercial, and industrial development surrounding the project area. The entire
project area is located within the 100-year floodplain.
Wetland Values
The project area provides functions and values related to surface water storage and flood
compensation. Numerous forested and emergent wetlands are adjacent to the river throughout
the project area and serve to provide flood storage during significant storm events. The banks
and floodplains of portions of the project area, particularly along major roadways and near the
Pawtuxet Village, are developed and provide more limited flood storage protection.
Proposed Impacts
According to HEC-RAS modeling performed for the hydraulic analysis (Appendix F), surface
water elevations upstream of the dam will decrease with partial removal of the dam.
Downstream of the existing dam, WSEs will remain unchanged. Since any change in WSE is a
decrease, the change in WSEs for proposed conditions were determined to have no negative
impacts on existing flood storage capacity. In addition, the partial removal of the dam will help
to restore river flow to pre-dam conditions. Refer to the hydraulic analysis for further
information. As noted above, proposed action will improve flood protection and public safety in
the LPR and will reduce property flooding impacts upstream of PFD.
3.1.4.4
Groundwater and Surface Water Supplies
Drainage characteristics of the Pawtuxet River within the proposed project area have been
previously described. The Pawtuxet River is classified by RIDEM as a Class 5 water body under
the state’s CALM under RIDEM’s 2008 Integrated Water Quality Monitoring and Assessment
Report. This classification indicates that the lower Pawtuxet is “Impaired or threatened for one
or more designated uses by a pollutant(s).”
According to RIDEM’s “Rules and Regulations for Groundwater Quality”, groundwater in the
project area is classified as GB. Groundwater classified as GB may not be suitable for drinking
water use without treatment due to known or presumed degradation. There is no goal to restore
groundwater classified GB to drinking water quality.
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Wetland Functions and Values
The LPR and associated project area are set within a highly urbanized environment with
extensive pavement and non-porous surfaces. As such, areas surrounding the project area do not
function to provide groundwater recharge to the local aquifer. The Pawtuxet River does not
provide water to any public drinking water reservoirs in the project area.
Proposed Impacts
The proposed project will have no expected effect on groundwater and surface water supplies.
The project footprint will not increase impermeable surfaces within the already highly developed
LPR watershed.
The proposed project will restore more natural flow characteristics to the LPR. Immediately
upstream of the PFD, surface water elevations will decrease as a result of the partial removal of a
portion of the PFD. Downstream surface water elevations will experience little to no change.
Springtime floods will continue to influence vegetation communities within adjacent wetlands.
The reach of the LPR within the project area will remain a perennial stream with year-round flow
following the completion of the proposed project.
3.1.4.5
Water Quality
Drainage characteristics of the Pawtuxet River within the proposed project area have been
previously described.
Wetland Functions and Values
The Pawtuxet River is classified by RIDEM as a Class 5 water body under the state’s
consolidated assessment and listing methodology (CALM) under RIDEM’s 2008 Integrated
Water Quality Monitoring and Assessment Report. This classification indicates that the lower
Pawtuxet is “Impaired or threatened for one or more designated uses by a pollutant(s).”
The Pawtuxet River has a long history of industrial use, such as the Ciba-Geigy facility located
upstream of the dam in the LTRA, that has resulted in poor water and sediment quality. The
fringing floodplain wetland adjacent to the river helps to slow storm flows and filter out
sediment, helping to improve water quality.
Water Quality Analysis
The proposed project will improve water quality in the Lower Pawtuxet River, primarily by
reducing thermal and residence time impacts of the existing PFD impoundment. The partial
removal of the dam will not result in stormwater inputs. Dam removals and the restoration of
natural riverine function have been shown to increase water quality due to increased dissolved
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oxygen levels and improved water temperatures. By reducing temperature and residence time,
the project may reduce bacterial production and is expected to reduce nuisance algae production
and eutrophication.
Proposed Impacts
The proposed project will not result in negative impacts to water quality and, in fact, is expected
to provide significant improvements. As stated in Section 1.3.3, water levels in the LPR will be
lowered, and flow velocities will be restored to more natural conditions as a result of partial dam
removal. These changes, however, will not result in significant changes in river characteristics,
such as sediment transport, under existing versus proposed conditions. As a result, negative
impacts in water quality functions and values are not anticipated.
3.2
Soil Erosion and Sediment Control
Erosion and sediment control best management practices (i.e., hay bales, silt fencing, absorbent
boom, and possibly cofferdams) will be installed prior to the start of construction. The proposed
project involves the removal of the southern portion of the dam. A cofferdam may be installed if
necessitated by construction requirements. The project also involves stabilization and restoration
of the riverbanks post-construction. All disturbed areas will be stabilized with specific seed
mixes, containerized plantings, or other bioengineering elements as discussed in Section 1.4.
3.3
Alternatives to the Proposed Action
In developing the LPRRP, the project team, including RIDEM, evaluated all potentially feasible
alternatives, including the no-action alternative, before agreeing unanimously that the proposed
partial dam removal provides the greatest ecological benefits to the fisheries, wetlands and
waters of the Pawtuxet River, its watershed and Narragansett Bay. Two alternatives analysis
reports have been developed for this project (Pawtuxet River Anadromous Fish Passage
Restoration Project Feasibility Study by Kleinschmidt and Pawtuxet River Restoration
Alternatives Assessment by MMI) which evaluated a number of alternatives. Alternatives to the
proposed action include: full removal of the PFD, placement of a rock ramp, construction of a
Denil-style fish ladder, and the no action alternative, as described below.
3.3.1
Full Dam Removal Alternative
The Full Dam Removal Alternative at PFD was evaluated and rejected by the project team
because this alternative would not provide sufficient depths for migratory fish passage at
Pawtuxet Falls under all flow conditions without the need for extensive modification of the
bedrock. The reason this alternative would not provide historic depths at Pawtuxet Falls is
believed to be the interbasin transfer of roughly millions of gallons of water per day from the
Scituate Reservoir, which reduces main stem flow in the LPR particularly under low-flow
conditions. The full dam removal option would therefore not provide optimal restoration or
fisheries benefits and would not provide comparable restoration of wetland functions and values
as the selected alternative.
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3.3.2
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Placement of a Rock Ramp
Rock ramps are gradually sloping constructed riffles created to allow fish migration over an
existing dam. These structures are typically located at the downstream face of the dam and
extend downstream, but they can be placed in other locations as well. They are used where a
dam cannot be removed due to pool usage, the need for sediment retention, or flood control
issues.
Rock ramps do not fully restore the function of a river system since in typical applications the
subject dam remains in place when they are installed. They do not convert the pool to a freeflowing river. Their sole purpose is the provision of fish passage by easing the transition in
grade that occurs at a dam or other obstruction in the channel bed.
Placement of a rock ramp on the downstream face of the existing PFD was initially considered
for this project but was determined to be unbuildable. Construction of such a structure would
have aesthetic impacts at Pawtuxet Village given that with an average spillway height of four
feet and bedrock sloping downstream, the required length of the rock ramp would extend under
the Broad Street Bridge.
Moreover, even if the engineering and regulatory challenges presented by this alternative could
be met, it would not provide comparable ecological, water quality and flood control benefits as
the selected alternative, as it would not restore more natural flow characteristics to the LPR.
3.3.3 Construction of a Denil Fish Ladder
Structural fishways are designed to allow one or more target fish species to migrate upstream
past an existing dam. These man-made structures are designed to pass specific species and life
stages of fish with design accommodating the weakest of the target fish species, or the most
behaviorally limited species in the system. For example, in the Pawtuxet River system, shad is
the limiting species for fish ladder design. Since shad will not easily pass an Alaskan steep pass
and the amount of potential upstream habitat is well suited for shad, use of a Denil fishway was
evaluated here.
Denil fish ladders are rectangular chutes or flumes typically two to four feet wide and four to
eight feet deep with baffles that extend from the sides and bottom that act to dissipage the
water’s energy. This type of ladder can accommodate a variety of fish species and has a great
deal of success in passing diadromous and riverine fish. Proper inlet location must be considered
in placing the ladder to maximize fish passage efficiency. The fish inlet must provide a highly
attractive entrance for fish at the base of the dam.
Aesthetically, fish ladders are not always attractive features and often stand out in the
surrounding landscape. Fish ladders require regular maintenance to clean out debris and
maintain the structural integrity of the ladder. The most intensive maintenance occurs during the
upstream migration season, between late March and early April through mid-June. During that
time period, the primary concern is to keep the fishway clean from debris that can block passage.
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This maintenance is typically conducted twice each week; however, depending on the site, it
could be more or less frequent. Some fish ladders are inspected and cleaned on a daily basis.
This regular maintenance is normally done manually and so access to the fish ladder is
imperative. Minor adjustments to the stop logs in the entrance channel are also periodically
required. This would typically be done two or three times a season for this type of fishway and
its location. RIDEM estimates annual maintenance costs of a fish ladder at $20,000 to $30,000,
typically borne by the agency.
The fish ladder alternative was considered and rejected by the project team because this
alternative would not provide comparable ecological, water quality, and flood control benefits as
the selected alternative, as it would not restore more natural flow characteristics to the LPR.
Moreover, although well-designed fish ladders can be quite successful in passing target species
such as herring and shad, they do not pass as wide a range of species as do dam removals, and
therefore would not restore wetland wildlife diversity to the same extent. In the case of the
Pawtuxet River, for example, American eel and striped bass are two of the many species which
are expected to utilize the LPR habitat following partial dam removal, but which do not generally
ascend Denil fish ladders.
3.3.4 No Action Alternative
The No Action Alternative would leave the PFD in its current state. The dam would remain an
obstruction to fish passage and benefits to the State’s fisheries, wetlands, and water quality
associated with the LPRRP would not be realized. The existing dam structure would continue to
deteriorate, requiring maintenance or replacement at a future date. The project team therefore
rejected this alternative.
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References
Page 1 of 1
June 2010
REFERENCES
American Rivers. 2002. The Ecology of Dam Removal: A Summary of Benefits and Impacts.
American Rivers, Washington D.C.
Ciba Geigy Corporation. 1996. RCRA Facility Investigation: Pawtuxet River Corrective
Measures Study. Woodward-Clyde, Wayne, New Jersey.
Ciba Geigy Corporation. 2003. Sediment Sampling Report for the Pawtuxet River, Former Ciba
Geigy Facility, Cranston, Rhode Island. Woodward-Clyde, Wayne, New Jersey.
Cronon, W. 1983. Changes in the land: Indians, colonists, and the ecology of New England.
Hermes, O.D., L.P. Gromet, and D.P. Murray. 1994. Bedrock Geologic Map of Rhode Island.
Office of Rhode Island State Geologist.
Kleinschmidt. 2005. Pawtuxet River Anadromous Fish Passage Restoration Project Feasibility
Study. Kleinschmidt Energy and Water Resource Consultants, Essex, CT.
Milone & MacBroom, Inc. 2008. Pawtuxet River Restoration Alternatives Assessment. Milone &
MacBroom, Inc., Cheshire, CT.
National Oceanic and Atmospheric Administration. 2008. Technical Memorandum: Pawtuxet
River Wetlands and Potential Impacts.
Public Archaeology Laboratory, Inc. 2006. Technical Memorandum National Register
Eligibility Evaluation: Pawtuxet Falls Dam, Cranston and Warwick, Rhode Island. PAL
No. 1893. September 5, 2006.
Rector, D. 1981. Soil Survey of Rhode Island. U.S. Department of Agriculture, Soil
Conservation Service.
Rhode Island Department of Environmental Management. 2007. Rules and Regulations
Governing the Administration and Enforcement of the Fresh Water Wetlands Act.
Rhode Island Department of Environmental Management Division of Fish and Wildlife. 2005.
State Wildlife Conservation Strategy.
http://www.dem.ri.gov/programs/bnatres/fishwild/swgindex.htm
Rhode Island Department of Environmental Management Division of Fish and Wildlife. 2002.
Strategic Plan for the Restoration of Anadromous Fishes to R.I. Coastal Streams.
Walter, R. and D. Merritts. 2008. Natural streams and the legacy of water-powered mills.
Science, 18 January 2008, pp. 299-304.
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Pawtuxet River Restoration Project Pawtuxet River

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