flood insurance study

Transcription

FLOOD
INSURANCE
STUDY
STAFFORD COUNTY,
VIRGINIA
(ALL JURISDICTIONS)
COMMUNITY NAME
STAFFORD COUNTY
(ALL JURISDICTIONS)
Stafford County
COMMUNITY NUMBER
510154
Please note: this Preliminary FIS Report only includes revised coastal data and
riverine updates. The unrevised components will appear in the final FIS report.
PRELIMINARY:
August 16, 2013
Revised:
Federal Emergency Management Agency
FLOOD INSURANCE STUDY NUMBER
510154V000B
NOTICE TO
FLOOD INSURANCE STUDY USERS
Communities participating in the National Flood Insurance Program have established repositories
of flood hazard data for floodplain management and flood insurance purposes. This Flood
Insurance Study may not contain all data available within the repository. It is advisable to contact
the community repository for any additional data.
Part or all of this Flood Insurance Study may be revised and republished at any time. In addition,
part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which
does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the
responsibility of the user to consult with community officials and to check the community
repository to obtain the most current Flood Insurance Study components.
Initial Countywide FIS Effective Date:
February 4, 2005
Revised countywide FIS Date:
Please note: this Preliminary FIS Report only includes revised coastal data and
riverine updates. The unrevised components will appear in the final FIS report.
TABLE OF CONTENTS
Page
1.0
2.0
3.0
4.0
INTRODUCTION
1
1.1
Purpose of Study
1
1.2
Authority and Acknowledgments
1
1.3
Coordination
2
AREA STUDIED
3
2.1
Scope of Study
3
2.2
Community Description
6
2.3
Principal Flood Problems
8
2.4
Flood Protection Measures
9
ENGINEERING METHODS
10
3.1
Hydrologic Analyses
11
3.2
Hydraulic Analyses
15
3.3
Coastal Analyses
18
3.4
Vertical Datum
27
FLOODPLAIN MANAGEMENT APPLICATIONS
27
4.1
Floodplain Boundaries
28
4.2
Floodways
29
5.0
INSURANCE APPLICATIONS
48
6.0
FLOOD INSURANCE RATE MAP
49
7.0
OTHER STUDIES
51
8.0
LOCATION OF DATA
51
9.0
BIBLIOGRAPHY AND REFERENCES
52
i
TABLE OF CONTENTS - continued
Page
FIGURES
Figure 1 – Transect Location Map
23
Figure 2 – Typical Transect Schematic
26
Figure 3 – Floodway Schematic
48
TABLES
Table 1 - Summary of Discharges
12-15
Table 2 – Summary of Stillwater Elevations
20
Table 3 – Transect Data
24-25
Table 4 – Floodway Data
30-47
Table 5 - Community Map History
50
EXHIBITS
Exhibit 1 - Flood Profiles
Accokeek Creek
Aquia Creek
Austin Run
Claiborne Run
England Run
Falls Run
Little Falls Run
Potomac Creek
Rappahannock River
Rappahannock River - Left Channel
Rocky Run
Tributary 3 to Austin Run
Tributary 1 to Chopawamsic Creek
Tributary 1 to Rappahannock River
Whitsons Run
Exhibit 2 - Flood Insurance Rate Map Index
Flood Insurance Rate Map
ii
Panels 01P-08P
Panels 09P-17P
Panels 18P-22P
Panels 23P-27P
Panels 28P-36P
Panels 37P-42P
Panels 43P-46P
Panels 47P-48P
Panels 49P-51P
Panel 52P
Panels 53P-54P
Panel 55P
Panels 56P-58P
Panels 59P-60P
Panels 61P-64P
FLOOD INSURANCE STUDY
STAFFORD COUNTY, VIRGINIA (ALL JURISDICTIONS)
1.0
INTRODUCTION
1.1
Purpose of Study
This countywide Flood Insurance Study (FIS) revises and updates previous
FIS’s / Flood Insurance Rate Maps (FIRMs) in the geographic area of
Stafford County, Virginia, and aids in the administration of the National Flood
Insurance Act of 1968 and the Flood Disaster Protection Act of 1973.
This FIS has developed flood-risk data for various areas of the community that
will be used to establish actuarial flood insurance rates. This information will
also be used by Stafford County to update existing floodplain regulations as
part of the Regular Phase of the National Flood Insurance Program (NFIP), and
will also be used by local and regional planners to further promote sound
land use and floodplain development. Minimum floodplain management
requirements for participation in the NFIP are set forth in the Code of Federal
Regulations at 44 CFR, 60.3.
In some states or communities, floodplain management criteria or regulations
may exist that are more restrictive or comprehensive than the minimum Federal
requirements. In such cases, the more restrictive criteria take precedence, and
the State (or other jurisdictional agency) shall be able to explain them.
1.2
Authority and Acknowledgments
The sources of authority for this FIS are the National Flood Insurance Act of
1968 and the Flood Disaster Protection Act of 1973.
This FIS was prepared to include the unincorporated areas of Stafford County in
a countywide format FIS. Information on the authority and acknowledgments
included in this countywide FIS, as compiled from previously printed FIS
reports, is shown below.
For the May 1980 FIS report and November 19, 1980, FIRM, the hydrologic
and hydraulic analyses were prepared by Harris-Toups Associates for the
Federal Emergency Management Agency (FEMA), under Contract No.
H-3965. The work for the original study was completed in February 1978.
The hydrologic a n d hydraulic analyses for the Rappahannock R i v e r in the
original studies were performed previously by the Norfolk District of the
U.S. Army Corps of Engineers (USACE).
For the June 18, 1990, FIS, updated topographic and hydraulic data were
prepared by Bengtson, DeBell, Elkin & Titus, Ltd.; and Dewberry & Davis,
LLC, respectively, under agreement with FEMA. The work for that revised
study was completed in April 1989.
1
1
In the March 3, 1992, FIS, updated topographic, hydrologic, and hydraulic
data were prepared for Austin Run and Tributary 3 to Austin Run by
Springfield Engineering Corporation. That work was completed in October
1990.
The hydrologic and hydraulic analyses for the February 4, 2005, revision
were prepared by the USACE, Norfolk District, for FEMA, under InterAgency Agreement No. EMW-96-IA-0294, Project Order No. 1. That work
was completed in December 2000.
The base map information shown on the February 4, 2005, FIRM (Exhibit 2)
was derived from planimetric digital base map files provided by the Stafford
County Geographical Information System Office, 1300 Courthouse Road, P.O.
Box 339, Stafford, Virginia 22555-0339. The base map information was
photogrammetrically compiled at a scale of 1:2,400 from aerial photography
dated 2001. Within Marine Corps Base Quantico, major roads and drainage
was derived from U.S. Geological Survey (USGS) Digitial Orthophoto
Quadrangles produced at a scale of 1:12,000 from photography dated 1994 or
later.
The coordinate system used for the production of the February 4, 2005 digital
FIRM is Universal Transverse Mercator (UTM), Zone 18, referenced to the
North American Datum of 1983 (NAD 83)/ High Accuracy Reference Network
(HARN), Geodetic Reference System 1980 (GRS 80) spheroid.
For this new countywide revision, the coastal analysis and mapping for Stafford
County were conducted for FEMA by the USACE and its project partners
under Project Nos. HSFE03-06-X-0023 and HSFE03-09-X-1108. The coastal
analysis involved transect layout, field reconnaissance, erosion analysis, and
overland wave modeling including wave setup, wave height analysis and wave
runup.
The base map information shown on this new countywide revision FIRM was
provided by the Commonwealth of Virginia through the Virginia Base
Mapping Program (VBMP). The orthophotos were flown in 2009 at scales of
1:100 and 1:200.
The projection for this new countywide revision is Virginia State Plane South
zone. The horizontal datum is the NAD 83/HARN, GRS 80 spheroid.
Differences in datum, spheroid, projection, or UTM zones used in the
production of the FIRMs for adjacent jurisdictions may result in slight
positional differences in map features across jurisdictional boundaries. These
differences do not affect the accuracy of this FIRM.
1.3
Coordination
An initial Consultation and Coordination Officer's (CCO) meeting is held
typically with representatives of FEMA, the community, and the study
2
contractor to explain the nature and purpose of a FIS and to identify the streams
to be studied by detailed methods. A final CCO meeting is held typically
with representatives of FEMA, the community, and the study contractor to
review the results of the study.
For the March 3, 1992, FIS, an initial CCO meeting was held in February
1976, with representatives from FEMA, the county, the Virginia State Water
Control Board, and the study contractor to select the county base map and to
identify local flooding problems.
Regional drainage area-peak discharge relationships used for the detailed and
approximate study methods were coordinated with those used elsewhere in
the area by the USGS and the USACE. Peak discharges, flood elevations,
flood boundaries, and floodway delineations were reviewed by county
officials and officials of the State Water Control Board.
On January 9, 1980, a final CCO meeting was held with representatives
from FEMA, the State Water Control Board, the county, and the study
contractor to review the results of the original study.
For the February 4 , 2 0 0 5 revision, an initial CCO meeting was held on
November 21, 1996, and was attended by representatives of FEMA, Stafford
County, and the USACE (the study contractor) to explain the nature and
purpose of the study, the scope and limits of the work, and to obtain flood
information currently available concerning the county.
Contacts with various local, state, and Federal agencies were made during
the study in order to minimize possible hydrologic and hydraulic conflicts. A
search for basic data was made at all levels of Government.
On March 6, 2001, the results of this study were reviewed at a final CCO
meeting attended by representatives of FEMA, Stafford County, and the
USACE.
For this new countywide revision, the FEMA Region III office initiated a
coastal storm surge study in 2008 for the Atlantic Ocean, the Chesapeake Bay
and its tributaries, and the Delaware Bay. Therefore, no initial CCO meeting
for the coastal storm surge study was held.
For this new countywide revision, a final CCO meeting was held on
_____________, with representatives from FEMA, the study contractor, and
Stafford County.
2.0
AREA STUDIED
2.1
Scope of Study
This FIS covers the geographic area of Stafford County, Virginia.
In the original study, the following streams were studied by detailed
methods: Accokeek Creek, Aquia Creek, Tributary 1 to Chopawamsic
3
Creek, Claiborne Run, Falls Run, Little Falls Run, Potomac Creek, the
Rappahannock River, Rappahannock River-Left Channel around Laucks
Island, and Tributary 1 to the Rappahannock River. The first revision was
performed in order to incorporate updated topographic data and an updated
hydraulic analysis for Aquia Creek, from a point approximately 2,025 feet
downstream of the U.S. Route 1 bridge to the Beaver Dam. The 1992 FIS
was performed in order to incorporate updated topographic data and
hydrologic and hydraulic analyses for Austin Run, from a point
approximately 620 feet downstream of U.S. Route 1 to a point approximately
100 feet upstream of Interstate 95; and Tributary 3 to Austin Run, from its
confluence with Austin Run to a point approximately 5,800 feet upstream.
The areas studied by detailed methods were selected with priority given to
all known flood hazard areas and areas of projected development and
proposed construction.
For the February 4, 2005 revision, Tributary 1 to Austin Run and Tributary 2
to Austin Run had name changes, and they are now called Whitsons Run and
Rocky Run, respectively.
For the February 4, 2005 revision, the following streams were studied by
detailed methods and revised from the previous FIS dated March 3, 1992:
Limits of Revised or New Detailed
Stream Study
Accokeek Creek
From approximately 3,470 feet downstream
of Raven Road, State Route 609
to approximately 350 feet upstream of
Ramoth Church Road, State Route 628.
Aquia Creek
From the confluence with the Potomac River
to approximately 925 feet upstream of
Tacketts Mill Road, State Route 612.
Austin Run
From the confluence with Aquia Creek to
approximately 285
feet
upstream
of Winding Creek Road, State Route 628.
Claiborne Run
From the confluence with the Rappahannock
River to approximately 0.56 mile
upstream of Jefferson Davis Highway,
U.S. Route 1.
England Run
River to approximately 1.04 miles
upstream of Sanford Drive, State Route
670.
4
Limits of Revised or New Detailed
Stream Study
England Run
upstream of Sanford Drive, State Route
670.
Falls Run
upstream of Cardinal Forest Drive.
Little Falls Run
River to approximately 0.52 mile
upstream of White Oak Road, State
Route 218.
Rocky Run
From the confluence with Tributary 3 to
Austin Run to approximately 300 feet
upstream of Rockdale Road, State Route
617.
From the confluence with Austin Run to
approximately 1,510 feet upstream of
northbound Interstate 95.
Whitsons Run
From the confluence with Austin Run to
approximately 0.65 mile upstream of
Eustace Road, State Route 751.
The February 4, 2005 revision previously incorporated the determination of
two Letter of Map Revisions (LOMRs) issued by FEMA. The FIS
incorporated a LOMR for Chopawamsic Creek and Tributary 1 to
Chopawamsic Creek, effective September 30, 1992, to reflect updated
topographic information, hydraulic and hydrologic analyses. The LOMR for
Tributary 5 to Aquia Creek, effective July 24, 2002, incorporated updated
topographic information.
The February 4, 2005 revision also incorporates the as-built conditions data
for two conditional LOMRs without the issuance of as-built LOMRs. These
conditional LOMRs are as follows: conditional LOMR for Falls Run,
issued June 2, 1997, was incorporated to reflect updated topographic
information and conditional LOMR for Rocky Run, issued May 24, 2001,
was incorporated to reflect updated hydraulic analyses.
For this revision, the determination of one LOMR issued by FEMA was
incorporated. This FIS incorporates a LOMR for Tributary 5 to Aquia
Creek, effective May 17, 2012, to reflect updated topographic information, and
hydraulic and hydrologic analyses.
5
Limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and
on the FIRM (Exhibit 2). The areas studied by detailed m et h od s were
selected with priority given to all known flood hazard areas and areas of
projected development and proposed construction.
This revision incorporates new detailed coastal flood hazard analyses for the
Rappahannock River, Aquia Creek, Austin Run, Potomac Creek, and Quantico
Creek. Study efforts were initiated in 2008 and concluded in 2012.
Approximate analyses were used to study those areas having a low development
potential or minimal flood hazards. The scope and methods of study were
proposed to, and agreed upon by, FEMA and King George County.
2.2
Community Description
Stafford County is located in the northern portion of Virginia. The county
is bordered by the unincorporated areas of Prince William County to the north;
the unincorporated areas of King George County and the Potomac River to the
east; the City of Fredericksburg and the unincorporated areas of Caroline
County and Spotsylvania County to the south; and the unincorporated areas of
Culpeper and Fauquier Counties to the west. The county is approximately 40
miles south of Washington, D.C., and approximately 55 miles north of the
City of Richmond. The county has a total land area of 277 square miles. The
Quantico Marine Corps Base, located in the northern part of the county,
encompasses 21 percent of Stafford County's land (Internet web site, Stafford
County, 2000).
Stafford County was formed in 1664 and named for Staffordshire, England.
Several historical landmark structures can be found in the county. The
boyhood home of George Washington, Ferry Farm, is located on the
Rappahannock River in southern Stafford County. Others include the 18th
century Chatham manor house, the Belmont home of American impressionist
artist Gari Melchers, and Aquia Church, built in 1751. In Colonial times,
Falmouth, located on the north bank of the Rappahannock River, was a major
port for the shipment of tobacco, wheat, com, and cotton. During the Civil
War, the Union Army of the Potomac camped within the county and left much
of the land and farms in ruins (Internet web site, Stafford County, 2000).
The location of the county with respect to the main East Coast transportation
corridors (U.S. Route 1 and Interstate 95) has been favorable for growth in
the county during the 20th century, and this trend is expected to continue.
The population was 24,587 in 1970, 61,236 in 1990, 92,446 in 2000, and
128,961 in 2010 (U.S. Census Bureau, QuickFacts, 2 0 1 3 ). The Aquia
Harbour subdivision had a population of 6,400, making it the largest
subdivision in the county. Much residential and commercial growth is taking
place in the Garrisonville area at the northern end of the county and along U.S.
Route 17 in southern Stafford County (Internet web site, Stafford County, 2000).
Stafford County is located along the Fall Line, an indefinite physiographic
boundary separating the crystalline bedrock complex of the Piedmont Plateau
to the western half of the county from the sediments of the Atlantic Coastal
Plain to the eastern half. The topography is gently rolling to hilly west of the
6
Fall Line and relatively flat to the east. In general, the county's land surface
slopes toward the southeast at about 20 feet per mile. Drainage of runoff is
provided by streams which flow into the Potomac River to the east and the
Rappahannock River to the south. The county's major soil types are deep,
poorly to well-drained clays and loams that are well suited for field crop
cultivation. Granite, sand, and gravel are present in certain areas. Crops
include hay, barley, corn, and wheat. Common types of natural vegetation
include Virginia pine, oak, hickory, and scrub oak (Clements, 1991).
Sedimentary formations of the Coastal Plain fall into two general categories.
The Potomac Group of the Cretaceous Era is formed by fluvial erosion and
deposition. The more recent Tertiary formations result from variations in
ancient sea levels. Stream drainage patterns in the Coastal Plain are more
advanced than in the more erosion-resistant Piedmont Plateau (Stafford County
Planning Commission, 1975).
The soils in Stafford County can be grouped into eight different soil
associations. On the western side of the county along the Fauquier County
boundary, located in the Piedmont uplands, the soils belong to the NasonElioak Manor association, which are deep, well-drained silt loams with
predominantly clay or silt loam subsoils. Sandy loam soils of the ApplingCecil-Ashlar association lie east of the Nason-Elioak-Manor association and are
located in the Quantico Marine Base, the area around Hartwood, and in the area
around Rocky Pen Run and the Rappahannock River. These soils are deep to
moderately deep, and well-drained to excessively drained, having dominantly
clay or fine sandy loam subsoil.
One of the larger soil associations in Stafford County extends from the northern
boundary south to State Route 17. Lying just west of the Fall Line, this group is
known as the Cullen-Mecklenburg-Orange association. These soils are deep,
well-drained to poorly drained loams having dominantly clay subsoils.
These soils are also found on Piedmont uplands. The Sassafras-AuraCaroline soil group occupies the northeastern section of the county, generally
from the Fall Line eastward to the Potomac River. Found on Coastal Plain
uplands, these soils are deep, well-drained sandy loams having sandy clay loam,
heavy clay loam, or clay subsoils.
The broad, low-lying areas near the mouths of Aquia Creek and Potomac Creek
are situated in the Tetotum-Bladen-Bertie association, which consists of deep,
moderately well-drained to poorly drained loams and sandy loams having
clayey subsoils. Along the Rappahannock River in the southeastern part of the
county are soils in the Wickham-Alta Vista-Dogue association. These are
deep, well- drained sandy loams found on stream terraces. A broad belt of
soils, extending from Horsepen Run southeast to the county line, lies in the
Bourne-Caroline association. These are generally deep, moderately well-drained
sandy loams with a clay fragipan. The soils in the area north of White Oak
and south of the Potomac River are either sandy loam or loamy sand in the
Marr-Westphalia association (U.S. Department of Agriculture, 1974).
The climate is typical of the temperate mid-Atlantic states. The average annual
temperature is 56 degrees Fahrenheit (°F), with monthly averages of 35°F
and 77°F in January and July, respectively. The average annual precipitation
7
is 41 inches. There is some variation in monthly averages; however, this
rainfall is distributed uniformly throughout the year. The annual snowfall
averages 17 inches. The average growing season extends from late-April to
mid-October, approximately 175 days (Clements, 1991).
The economy of the area is highly diversified, including industry,
agriculture, construction, education, and government. Major highways such as
Interstate 95 and U.S. Route 1, and the commuter rail system to Washington,
D.C., have played a major role in the rapid urbanization of the county. With
the county's many miles of streams and shoreline, there will be pressure for
future development in the floodplains.
2.3
Principal Flood Problems
Stafford County is bordered on the east by the Potomac River estuary, which
is subject to tidal flooding. The tide of record occurred in 1933, when tidal
elevations were 9 feet. The next most severe high tide occurred in 1954,
when Hurricane Hazel raised tidal elevations to 6 feet. The normal high tide is
1 foot. The USACE intermediate regional high tide, which has an average
recurrence interval of 100 years, was estimated at 9.5 feet for the Potomac
River at Stafford County (USACE, 1969).
For the streams studied in the February 4, 2005 revision, flooding may be
caused by heavy rain occurring any time of the year. Flooding may also
occur as a result of intense rainfall produced by local thunderstorms or
tropical disturbances such as hurricanes, which move into the area from the
Gulf or Atlantic coasts. Flood heights for the streams can rise from normal to
extreme flood peaks in a relatively short period of time. The amount and
extent of damage caused by fluvial flooding depends upon the size of the
area flooded, the height of flooding, the velocity of flow, the rate of rise, and
the duration of flooding. The rate of rise and duration of flooding depend
largely on the time required for flood waters to concentrate at a particular
point, and on the duration and intensity of flood- producing rainfall. Stream
velocities during floods depend largely on the size and shape of the cross
sections, roughness conditions of the stream which tend to retard the flow,
and the bed slope, all of which vary on different streams and at different
locations on the same stream. During all major floods, high velocity flood
flows and hazardous conditions would exist in the main stream channel.
There is one stream gaging station on the Rappahannock River near
Fredericksburg (No. 01668000). Historic floods between 1937 and 1955,
their discharges in cubic feet per second (cfs), and their estimated recurrence
interval as recorded by this gage are shown in the following tabulation (U.S.
Department of the Interior, 1976; U.S. Department of the Interior, 1968).
Year of Flood
Discharge
(cfs)_
1937
1943
1955
1972
134,000
140,000
74,000
107,000
8
Recurrence Interval
135 years
140 years
20 years
60 years
From 1951 to 1957, three gaging stations were located in the northern section
of the county, two on Chopawamsic Creek and one on Beaverdam Run (U.S.
Department of the Interior, 1968). These stations were used to develop flow
data for the analysis of hydrologic conditions prior to the construction of
Lunga Reservoir.
There are no damage figures available for the 1943 flood. However, the
Rappahannock River crested 45 feet above normal levels, causing a great deal
of damage that included two fatalities and the explosion of five gasoline
storage tanks (USACE, September 1970). Damage figures are available for
the 1972 storm caused by Tropical Storm Agnes. In the Potomac River basin
as a whole, damage totaled $129,128,000, most of which was to residential
properties. The subbasin of the Potomac River, downstream of Washington,
D.C., which includes the northern section of Stafford, suffered business and
agricultural losses (USACE, November 1974).
Damage figures were
unavailable for the Rappahannock River basin.
A discontinued stream gage (No. 01660400), maintained by the Virginia
Department of Environmental Quality (VDEQ), is located along Aquia Creek
near Garrisonville. The gage was discontinued in 1997. Records from
VDEQ show a maximum discharge of 11,600 cubic feet per second (cfs) for
the 1972 storm (U.S. Department of the Interior, 1998). Another stream gage
(No. 01660500), maintained by the USGS, is located in the Aquia Creek
watershed along the Beaverdam Run tributary near Garrisonville (U.S.
Department of the Interior, 2000). For the other streams studied in the
February 4, 2005 revision, records of stream flows are not available; however,
the community has experienced minor flooding where structures have
suffered some flood damage.
In August 2011, Hurricane Irene hit the eastern coast of the United States and
caused substantial damage. In September 2011, President Barack Obama
declared a Major Disaster Declaration for numerous counties, including Stafford
County, which allowed residents affected by the hurricane to apply for federal
aid. This declaration followed the August 2011 Emergency Declaration.
In October 2012, Hurricane Sandy made landfall north of the Commonwealth of
Virginia, but caused substantial damage in Virginia. President Obama declared
an Emergency Declaration for numerous counties, including Stafford County,
which allowed assistance for emergency work and the repair or replacement of
disaster-damaged facilities.
2.4
Flood Protection Measures
There are three reservoirs in Stafford County: the Lunga Reservoir on
Beaverdam Run, Smith Lake on Aquia Creek, and Abel Lake on Potomac
Creek. The impoundment on Beaverdam Run was constructed in 1957 for
recreation and water-supply purposes. It serves the Quantico Marine Corps
Base, and normally contains 9,600 acre-feet of water (Patterson, 1976). Smith
Lake, constructed in 1968, provides water to areas around Aquia.
Rehabilitation of Smith Lake was completed in 1996, increasing the normal
9
pool elevation from 70 feet to 90 feet. This impoundment contains
approximately 6,445 acre-feet of water (Stafford County comment letter, May
14, 2004). Abel Lake, constructed in 1965, also serves as a water-supply
impoundment. However, the principal spillway was designed to release that
part of the 100-year storm that cannot be confined in the 5,000 acre-feet of
storage provided for flood control. Both Lunga Reservoir and Smith Lake
serve minor flood control roles. A non-structural flood protection measure
can be found in the floodproofing ordinance of the Virginia Uniform
Statewide Building Code (Virginia State Board of Housing, 1975).
Zoning and building codes provide a means of nonstructural measures for
floodplain management. The "Uniform Statewide Building Code" which
went into effect in September 1973 states, "where a structure is located in a
100-year floodplain, the lowest floor or all future construction or substantial
improvement to an existing structure . . ., must be built at or above that level,
except for non- residential structures which may be floodproofed to that level"
(Commonwealth of Virginia, 1973). These requirements will no doubt be
beneficial in reducing future flood damages in the county.
3.0
ENGINEERING METHODS
For the flooding sources studied in detail in the county, standard hydrologic and
hydraulic study methods were used to determine the flood hazard data required for this
study. Flood events of a magnitude which are expected to be equaled or exceeded once
on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval) have
been selected as having special significance for floodplain management and for flood
insurance rates. These events, commonly termed the 10-, 2-, 1-, and 0.2-percent annual
chance floods, have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled
or exceeded during any year. Although the recurrence interval represents the long
term average period between floods of a specific magnitude, rare floods could occur at
short intervals or even within the same year. The risk of experiencing a rare flood
increases when periods greater than 1 year are considered. For example, the risk of
having a flood which equals or exceeds the 1 percent annual chance flood in any 50year period is approximately 40 percent (4 in 10), and, for any 90-year period, the risk
increases to approximately 60 percent (6 in 10). The analyses reported herein reflect
flooding potentials based on conditions existing in the community at the time of
completion of this study. Maps and flood elevations will be amended periodically to
reflect future changes.
FEMA adopted recommendations by the National Academy of Sciences (NAS) to
include prediction of wave heights in FISs for coastal communities subject to storm
surge flooding, and to report the estimated wave crest elevations as the base flood
elevations (BFE) on the FIRM (National Academy of Sciences, 1977).
Previously, FIRMs for these communities were produced showing only the stillwater
storm surge elevations due to the lack of a suitable and generally acceptable
methodology for estimating the wave crest elevations associated with storm surges.
These stillwater elevations were subsequently stipulated in community flood plain
management ordinances as the minimum elevation of the lowest floor, including
10
basement, of new construction. Communities and individuals had to consider the
additional hazards of velocity waters and wave action on an ad hoc basis. Because
there has been a pronounced tendency for buildings to be constructed only to meet
minimum standards, without consideration of the additional hazard due to wave
height, increasing numbers of people could unknowingly be accepting a high degree
of flood-related personal and property risk in coastal areas subject to wave action.
Therefore, FEMA has pursued the development of a suitable methodology for
estimating the wave crest elevations associated with storm surges. The recent
development of such a methodology by the NAS has led to the adoption of wave
crest elevations for use as the BFEs in coastal communities.
3.1
Hydrologic Analyses
Hydrologic analyses were carried out to establish the peak discharge- frequency
relationships for each flooding source studied in detail affecting the county.
Pre-countywide Analyses
In the original study, a log-Pearson Type III analysis was carried out using
the USGS hydrologic computer program based on Bulletin 17 and the annual
peaks of each of the gaging stations shown in the following tabulation (U.S.
Department of the Interior, 1976; Water Resources Council, 1976).
Gaging Station and Location
Period of Record
Difficult Run near Fairfax (No. 6457)
Difficult Run near Great Falls (No. 6460)
Accotink Creek near Annandale (No. 6540)
Cedar Run near Catlett (No. 6560)
Broad Run at Buckland (No. 6565) Bull Run
near Manassas (No. 6570) Occoquan Creek
near Occoquan (No. 6575)
20
41
29
25
25
25
26
Gaging Station and Location
Period of Record
South Fork Quantico Creek near Independent Hill
(No. 6585)
Opequon Creek near Berryville (No. 6150)
South Fork Shenandoah River at Front Royal (No. 6310)
North Fork Shenandoah River near Strasburg (No. 6340)
Cedar Creek near Winchester (No. 6345)
Passage Creek near Buckton (No. 6355)
Rappahannock River near Warrenton (No. 6620)
Rush River at Washington, Virginia (No. 6625)
Battle Run near Laurel Mills (No. 6628)
Hazel River near Rixeyville (No. 6635)
Rappahannock River at Remington (No. 6640)
Rappahannock River near Fredericksburg (No. 6680)
South Fork Shenandoah River (No. 6285)
24 years
32 years
51 years
50 years
39 years
43 years
33 years
22 years
17 years
35 years
33 years
67 years
45 years
11
years
years
years
years
years
years
years
From the results of the 1980 analysis, a regional relationship correlating
the drainage area with the peak flow was developed. This method was also used
for the streams studied by approximate methods in the county.
For the March 3, 1992, FIS, discharges for Austin Run and Tributary 3 to Austin
Run were calculated using the Soil Conservation Service’s TR-20 computer model
(U.S. Department of Agriculture, 1987).
The discharge-frequency relationships for each stream studied in detail in the
February 4, 2005, revision were determined using the USACE HEC-1 hydrologic
computer program (USACE 1991). Each watershed was divided into subareas and
the drainage areas, percent imperviousness, times of concentration, and routing
times for each subarea were determined. The percent imperviousness was based
on soil types and land uses that existed at the time of the study. Based on the
above basin parameters and rainfall data from Technical Paper No. 40 (TP-40)
(U.S. Department of Commerce, 1961) and NWS HYDR0-35 ( U.S. Department
of Commerce, 1977), flood hydrographs were computed for each subarea, routed
downstream and combined with other subareas using the HEC-1 computer
program. Discharges were modified due to "reservoir effects" encountered at
several high embankment railroad and highway structures which have relatively
high fills and small culvert capacities. The HEC-1 computer program was used to
route the flood hydrographs through these storage areas, thereby reducing the
discharge-frequency relationships downstream of these structures.
A summary of the drainage area-peak discharge relationships for the streams
studied by detailed methods is shown in Table 1, "Summary of Discharges."
TABLE 1 -SUMMARY OF DISCHARGES
FLOODING SOURCE
AND LOCATION
ACCOKEEK CREEK
Approximately 1,200 feet
downstream of State Route 609
Downstream of CSX Railroad
Upstream of CSX Railroad
Downstream of Interstate 95
Upstream of Interstate 95
upstream of Interstate 95
upstream of State Route 62
AQUIACREEK
At Government Island
Downstream of Smith Lake Dam
Upstream of Smith Lake Dam
At State Route 641
At State Route 612
DRAINAGE AREA
PEAK DISCHARGES (cfs)
(sq. miles)
10-YEAR 50-YEAR 100-YEAR 500-YEAR
18.40
13.30
13.30
8.25
8.25
4,880
3,520
4,810
3,110
5,050
7,550
4,870
7,540
4,190
8,060
8,490
5,310
8,520
4,550
9,200
11,050
6,570
11,180
5,570
12,240
5.74
3,660
5,900
6,740
8,980
82.26
1,600
2,580
2,950
3,940
62.40
55.90
55.90
35.10
9,440
9,190
10,400
9,580
15,100
14,800
16,400
15,000
17,000
16,700
18,400
17,000
22,900
22,600
24,400
22,500
14.00
4.44
5,860
2,720
9,140
4,350
10,400
4,980
13,700
6,630
12
TABLE 1 - SUMMARY OF DISCHARGES - continued
FLOODING SOURCE
AND LOCATION
AQUIACREEK
At Government Island
Downstream of Smith Lake Dam
Upstream of Smith Lake Dam
At State Route 641
At State Route 612
AUSTIN RUN
At confluence with Aquia Creek
At Interstate 95
At State Route 784
At State Route 628
CLAIBORNE RUN
At confluence with
Rappahannock River
Upstream of tributary located
. approximately 300 feet down. stream of State Route 623
At U.S. Route 1
ENGLAND RUN
At confluence with
Rappahannock River
downstream of State
Route 670
FALLS RUN
At confluence with
Rappahannock River
At Interstate 95
At State Route 654
upstream of Cardinal Drive
LITTLE FALLS RUN
At confluence with
Rappahannock River
At State Route 682
upstream of State
Route 218
DRAINAGE AREA
(sq. miles)
62.40
55.90
55.90
35.10
9,440
9,190
10,400
9,580
15,100
14,800
16,400
15,000
17,000
16,700
18,400
17,000
22,900
22,600
24,400
22,500
14.00
4.44
5,860
2,720
9,140
4,350
10,400
4,980
13,700
6,630
11.00
5.14
2.12
0.32
5,060
2,710
1,590
390
6,720
3,330
2,550
600
7,260
3,570
2,920
680
8,680
4,000
3,880
880
880
6.86
3,010
4,930
5,640
7,550
3.74
1.68
1,450
850
2,470
1,460
2,860
1,680
3,900
2,290
2.78
1,630
2,660
2,970
4,040
1.20
540
970
1,120
1,560
0.58
250
450
520
730
6.14
3.72
1.41
3,030
1,770
750
4,410
2,820
1,150
4,910
3,200
1,310
6,010
3,640
1,790
0.31
250
370
420
540
5.27
3.33
1,920
1,810
2,930
2,920
3,150
3,340
3,660
4,450
1.00
800
1,240
1,410
1,830
13
TABLE 1 - SUMMARY OF DISCHARGES - continued
FLOODING SOURCE
AND LOCATION
POTOMAC CREEK
Approximately 4,000
feet downstream of
U.S. Route 1
At U.S. Route 1
At Potomac Creek
Reservoir
DRAINAGE AREA
(sq. miles)
36.10
34.78
1,820
1,610
3,900
3,465
5,255
4,675
10,020
8,940
29.78
380
830
1,130
2,200
1,660.00
1,605.00
59,100
30,850
103,700
54,400
130,700
68,000
211,500
112,500
1,605.00
57,200
100,300
126,400
211,500
RAPPAHANNOCK
RIVER - LEFT CHANNEL
At outlet to the
Rappahannock River
1,605.00
26,350
45,900
58,400
99,000
ROCKY RUN
At confluence with
At State Route 617
1.97
0.52
RAPPAHANNOCK RIVER
downstream of confluence
of Little Falls Run
At inlet to Laucks Island
At upstream limit of
detailed study
TRIBUTARY 3 TO
AUSTIN RUN
At confluence with
Austin Run
Upstream of confluence
with Rocky Run
1,400
550
2,000
860
2,180
980
2,950
1,310
3.54
1,980
2,560
2,770
3,390
1.48
1,300
2,080
2,370
3,140
TRIBUTARY 1 TO
CHOPAWAMSIC CREEK
At confluence with
Chopawamsic Creek
0.89
390
860
1,175
2,290
TRIBUTARY 1 TO THE
RAPPAHANNOCK RIVER
At confluence with the
Rappahannock River
At Old Ferry Road
1.45
0.04
540
50
1,180
115
1,600
160
3,095
320
2.49
2,300
3,490
3,940
5,100
1.05
1,140
1,710
1,930
2,490
0.33
440
660
740
960
WHITSONS RUN
At confluence with
Austin Run
14
The effects of tidal flooding in Stafford County were determined by a
frequency analysis of the tidal gaging station at Washington, D.C., which
was in operation from 1931 to 1977 (Darling, 1977). The results of
this analysis were then adjusted for distance above the mouth of the
Potomac River.
The stillwater elevations have been determined for the 10-, 50-, 100-,
and 500- year floods have been determined for the Potomac River and
are summarized in Table 2, "Summary of Stillwater Elevations."
February 4, 2005 Countywide Analyses
No new hydrologic analyses were developed for this FIS.
This Countywide Analyses
No new hydrologic analyses were developed for this FIS.
3.2
Hydraulic Analyses
Hydraulic analyses, considering storm characteristics and the shoreline
and bathymetric characteristics of flooding from the sources studied, were
carried out to provide estimates of the elevations of floods of the selected
recurrence intervals along each of the shorelines.
For the previous study, cross-section data for the streams studied in detail
were obtained from aerial photographs and topographic maps at scales
of 1:1,200 and 1:2,400, with a 5-foot contour interval (Toups
Corporation of McLean, Virginia, 1977); the below-water cross sections
were obtained by field measurements. In order to compute the significant
backwater effects of bridges and culverts, cross sections were located
upstream and downstream of these structures, which were field surveyed
to obtain elevation data and structural geometry.
For the February 4, 2005 revision, cross sections for the backwater
analyses of the streams were obtained from field surveys and topographic
m a p s (Stafford County, 1983 and 1988; Air Survey Corporation, 1983)
and located at close intervals to bridges and culverts in order to compute
the backwater effects of these structures. Elevation data and structural
geometry for bridges, dams, and culverts were obtained from field
surveys or available engineering plans.
Locations of selected cross sections used in the hydraulic analyses are
shown on the Flood Profiles (Exhibit 1). For stream segments for which
a floodway was computed (Section 4.2), selected cross-section locations
are also shown on the FIRM (Exhibit 2).
15
For the March 3, 1992, FIS, water-surface elevations of floods of the
selected recurrence intervals were computed using the USACE HEC-2
step-backwater computer program (USACE, HEC-2 Water-Surface
Profiles. Generalized Computer Program, October 1973; USACE,
HEC-2 Water-Surface Profiles, Users Manual, October 1973; USACE,
May 1974). For the 1980 FIS, starting water-surface elevations for the
streams studied in detail were determined by the slope/area method, except
for Aquia Creek and the 100-year flood on the Rappahannock River. For
Aquia Creek, starting elevations were taken from the tidal data presented
in Table 2 for the Potomac River. The 100-year flood starting elevation for
the Rappahannock River was taken from the 1970 USACE study
(USACE, September 1970). For the 1992 FIS, the starting water-surface
elevations for Austin Run were taken from known elevations and hand
calculated to the limit of detailed study. Flood profiles were drawn
showing computed water-surface elevations for floods of the selected
recurrence intervals.
For the February 4, 2005 revision, water-surface elevations of floods of
the selected recurrence intervals were computed using the USACE HECRAS step-backwater computer program (USACE, 1998 and 1999).
Flood profiles were drawn showing computed water-surface elevations
for floods of the selected recurrence intervals. Starting water-surface
elevations for Tributaries 1 (Whitsons Run), 2 (Rocky Run), and 3 to
Austin Run were based on backwater effects from the main stem, due to
coincidental peak flooding. For all other streams in this revision, starting
water-surface elevations were determined using the slope/area method.
The February 4, 2005 revision also incorporates the determination of the
LOMR for Tributary 1 to Chopawamsic Creek, effective September 30,
1992. The water-surface elevations for this LOMR were computed using
USACE HEC-2 step-backwater computer program (USACE, HEC-2
Water-Surface Profiles, Generalized Computer Program, October 1973;
USACE, HEC-2 Water-Surface Profiles, Users Manual, October 1973;
USACE, May 1974).
For the March 3, 1992 study, channel roughness factors (Manning's "n")
used in the hydraulic computations for the streams studied by detailed
methods, except for the Rappahannock River, were assigned on the
basis of field inspections and previously published guidelines (U.S.
Department of Agriculture, 1963). Roughness factors for the
Rappahannock River were determined from the hydraulic analyses of past
floods. This analysis consisted of matching discharges with corresponding
historical flood profiles derived from high-water marks.
February 4, 2005 Countywide Analyses
For the February 4, 2005 revision, channel and overbank roughness
factors (Manning's "n") used in the hydraulic computations were based
on engineering judgment and field observations of the stream
and floodplain areas. The ranges of channel and overbank “n”
16
values for all detailed streams are shown as follows:
Stream
Accokeek Creek
Aquia Creek
Austin Run
Claiborne Run
England Run
Falls Run
Little Falls Run
Potomac Creek
Rappahannock River
Rappahannock RiverLeft Channel
Rocky Run
Tributary 1 to Chopawamsic Creek
Tributary 1 to the
Rappahannock River
Whitsons Run
Channel "n"
0.025-0.045
0.025-0.045
0.025-0.045
0.025-0.045
0.025-0.045
0.025-0.045
0.025-0.045
0.030-0.040
0.035-0.070
Overbank "n"
0.030-0.120
0.030-0.120
0.030-0.120
0.030-0.120
0.030-0.120
0.030-0.120
0.030-0.120
0.030-0.100
0.075-0.150
0.035
0.025-0.045
0.025-0.045
0.017-0.050
0.150
0.030-0.120
0.030-0.120
0.060-0.100
0.030-0.045
0.025-0.045
0.020-0.090
0.030-0.120
For the streams studied by approximate methods, flood elevations
were determined from a regional relation defined for estimating the depth
of flooding on natural-flow streams in Virginia having a recurrence
interval of 100 years (U.S. Department of the Interior, 1977). The
drainage area is the only independent variable required, and is related to the
depth of flow by the following equation:
D = 3.2A0 2
·
where D is the flood depth of the 100-year flood, in feet, and A is the
drainage area, in square miles.
The hydraulic analyses for the February 4, 2005, FIS were based on
unobstructed flow. The flood elevations shown on the profiles are thus
considered valid only if hydraulic structures remain unobstructed, operate
properly, and do not fail.
This Countywide Analyses
No new hydraulic analyses were developed for this FIS.
Qualifying bench marks (elevation reference marks) within a given
jurisdiction that are cataloged by the National Geodetic Survey (NGS) and
entered into the National Spatial Reference System (NSRS) as First or
Second Order Vertical and have a vertical stability classification of A, B,
or C are shown and labeled on the FIRM with their 6-character NSRS
Permanent Identifier.
17
Bench marks cataloged by the NGS and entered into the NSRS vary
widely in vertical stability classification.
NSRS vertical stability
classifications are as follows:
•
Stability A: Monuments of the most reliable nature, expected to
hold position/elevation (e.g., mounted in bedrock)
•
Stability B: Monuments which generally hold their position/
elevation (e.g., concrete bridge abutment)
•
Stability C: Monuments which may be affected by surface ground
movements (e.g., concrete monument below frost line)
•
Stability D: Mark of questionable or unknown vertical stability
(e.g., concrete monument above frost line, or steel witness post)
In addition to NSRS benchmarks, the FIRM may also show vertical
control monuments established by a local jurisdiction; these monuments
will be shown on the FIRM with the appropriate designations. Local
monuments will only be placed on the FIRM if the community has
requested that they be included, and if the monuments meet the
aforementioned NSRS inclusion criteria.
To obtain current elevation, description, and/or location information
for bench marks shown on the FIRM for this jurisdiction, please contact
the Information Services Branch of the NGS at (301) 713-3242, or visit
their Web site at www.ngs.noaa.gov.
3.3
Coastal Analyses
Coastal analyses considering storm characteristics and the shoreline and
bathymetric characteristics of the flooding sources studied, were carried out to
provide estimates of the elevations of floods for the selected recurrence
intervals along the shoreline. Users of the FIRM should be aware that coastal
flood elevations are provided in Table 2, “Summary of Stillwater Elevations”,
in this report. If the elevation on the FIRM is higher than the elevation shown
in this table, a wave height, wave runup, and/or wave setup component likely
exists, in which case, the higher elevation should be used for construction
and/or floodplain management purposes.
Development is moderate along shorefront areas of Stafford County and
includes residential development, agricultural areas, small commercial
facilities and military facilities. These areas are bisected, in numerous
locations, with expansive areas of parklands and undeveloped woodlands.
Elevations vary from sea level to approximately 280 feet NAVD 88. Behind
the shoreline, development is light.
An analysis was performed to establish the frequency peak elevation
relationships for coastal flooding in Stafford County. The FEMA Region III
office, initiated a study in 2008 to update the coastal storm surge elevations
18
within the states of Virginia, Maryland, and Delaware, and the District of
Columbia including the Atlantic Ocean, Chesapeake Bay including its
tributaries, and the Delaware Bay. The study replaces outdated coastal storm
surge stillwater elevations for all FISs in the study area, including Stafford
County, and serves as the basis for updated FIRMs. Study efforts were
initiated in 2008 and concluded in 2013.
The storm surge study was conducted for FEMA by the USACE and its
project partners under Project HSFE03-06-X-0023, “NFIP Coastal Storm
Surge Model for Region III” and Project HSFE03-09-X-1108, “Phase II
Coastal Storm Surge Model for FEMA Region III”. The work was performed
by the Coastal Processes Branch (HF-C) of the Flood and Storm Protection
Division (HF), U.S. Army Engineer Research and Development Center –
Coastal & Hydraulics Laboratory (ERDC-CHL) (USACE, 2012).
The end-to-end storm surge modeling system includes the Advanced
Circulation Model for Oceanic, Coastal and Estuarine Waters (ADCIRC) for
simulation of 2-dimensional hydrodynamics (Luettich and Westerink, 2008).
ADCIRC was dynamically coupled to the unstructured numerical wave model
Simulating WAves Nearshore (unSWAN) to calculate the contribution of
waves to total storm surge. The resulting model system is typically referred to
as SWAN+ADCIRC (Luettich and Westerink, 2008). A seamless modeling
grid was developed to support the storm surge modeling efforts. The modeling
system validation consisted of a comprehensive tidal calibration followed by a
validation using carefully reconstructed wind and pressure fields from three
major flood events for the Region III domain: Hurricane Isabel, Hurricane
Ernesto, and extratropical storm Ida. Model skill was accessed by quantitative
comparison of model output to wind, wave, water level, and high water mark
observations.
The tidal surge for those areas affected by the Potomac River affect the entire
shoreline within Stafford County. The entire Potomac River shoreline
coastline, from Potomac Creek to Chopawamsic Creek, is more prone to
damaging wave action during high wind events.
The storm-surge elevations for the 10-, 2-, 1-, and 0.2-percent annual chance
floods were determined for the flooding sources shown in Table 2, “Summary
of Stillwater Elevations.” The analyses reported herein reflect the stillwater
elevations due to tidal and wind setup effects.
19
TABLE 2 - SUMMARY OF STILLWATER ELEVATIONS
ELEVATION (feet NAVD 88*)
FLOODING SOURCE
AND LOCATION
10-PERCENT
2-PERCENT
1-PERCENT
0.2-PERCENT
At confluence of Potomac Creek
4.4
5.8
6.3
7.2
At confluence of Aquia Creek
4.4
5.8
6.3
7.4
At confluence of Chopawamsic Creek
4.6
5.8
6.1
7.7
POTOMAC RIVER
*North American Vertical Datum of 1988
The methodology for analyzing the effects of wave heights associated with
coastal storm surge flooding is described in a report prepared by the NAS
(National Academy of Sciences, 1977). This method is based on three
major concepts. First, depth-limited waves in shallow water reach
maximum breaking height that is equal to 0.78 times the stillwater depth.
The wave crest is 70 percent of the total wave height above the stillwater
level. The second major concept is that wave height may be diminished by
dissipation of energy due to the presence of obstructions, such as sand
dunes, dikes and seawalls, buildings and vegetation. The amount of energy
dissipation is a function of the physical characteristics of the obstruction and
is determined by procedures prescribed in the NAS report. The third major
concept is that wave height can be regenerated in open fetch areas due to the
transfer of wind energy to the water. This added energy is related to fetch
length and depth.
The coastal analysis and mapping for Stafford County was conducted for
FEMA by RAMPP under contract No. HSFEHQ-09-D-0369, Task Order
HSFE03-09-0002. The coastal analysis involved transect layout, field
reconnaissance, erosion analysis, and overland wave modeling including
wave setup, wave height analysis and wave runup.
Wave heights were computed across transects that were located along
coastal areas of Stafford County, as illustrated on the FIRM. The transects
were located with consideration given to existing transect locations and to
the physical and cultural characteristics of the land so that they would
closely represent conditions in the locality.
Each transect was taken perpendicular to the shoreline and extended inland
to a point where coastal flooding ceased. Along each transect, wave heights
and elevations were computed considering the combined effects of changes
in ground elevation, vegetation, and physical features. The stillwater
elevations for a 1% annual chance event were used as the starting elevations
20
for these computations. Wave heights were calculated to the nearest 0.1 foot,
and wave elevations were determined at whole-foot increments along the
transects. The location of the 3-foot breaking wave for determining the
terminus of the Zone VE (area with velocity wave action) was computed at
each transect.
A review of the geology and shoreline type in Stafford County was made to
determine the applicability of standard erosion methods, and FEMA’s
standard erosion methodology for coastal areas having primary frontal
dunes, referred to as the “540 rule,” was used (FEMA, 2007a). This
methodology first evaluates the dune’s cross-sectional profile to determine
whether the dune has a reservoir of material that is greater or less than 540
square feet. If the reservoir is greater than 540 square feet, the “retreat”
erosion method is employed and approximately 540 square feet of the dune
is eroded using a standardized eroded profile, as specified in FEMA
guidelines. If the reservoir is less than 540 square feet, the “remove”
erosion method is employed where the dune is removed for subsequent
analysis, again using a standard eroded profile. The storm surge study
provided the return period stillwater elevations required for erosion
analyses. Each cross-shore transect was analyzed for erosion, when
applicable.
Wave height calculations used in this study follow the methodologies
described in the FEMA guidance for coastal mapping (FEMA, 2007b).
Wave setup results in an increased water level at the shoreline due to the
breaking of waves and transfer of momentum to the water column during
hurricanes and severe storms. For the Stafford County study, wave setup
was determined directly from the coupled wave and storm surge model. The
total stillwater elevation (SWEL) with wave setup was then used for
simulations of inland wave propagation conducted using FEMA’s Wave
Height Analysis for Flood Insurance Studies (WHAFIS) model Version 4.0
(FEMA, 2007c). WHAFIS is a one-dimensional model that was applied to
each transect in the study area. The model uses the specified SWEL, the
computed wave setup, and the starting wave conditions as input.
Simulations of wave transformations were then conducted with WHAFIS
taking into account the storm-induced erosion and overland features of each
transect. Output from the model includes the combined SWEL and wave
height along each cross-shore transect allowing for the establishment of
BFEs and flood zones from the shoreline to points inland within the study
area.
Wave runup is defined as the maximum vertical extent of wave uprush on a
beach or structure. FEMA’s 2007 Guidelines and Specifications require the
2% wave runup level be computed for the coastal feature being evaluated
(cliff, coastal bluff, dune, or structure) (FEMA, 2007b). The 2% runup level
is the highest 2 percent of wave runup affecting the shoreline during the 1percent-annual-chance flood event. Each transect defined within the study
area was evaluated for the applicability of wave runup, and if necessary, the
appropriate runup methodology was selected and applied to each transect.
Runup elevations were then compared to WHAFIS results to determine the
dominant process affecting BFEs and associated flood hazard levels.
21
Computed controlling wave heights at the shoreline range from 2.6 feet to
7.9 feet. The corresponding wave elevation at the shoreline varies from 7.9
feet NAVD 88 to 9.3 feet NAVD 88. Vertical reinforced coastlines serve to
reduce wave height z.
Between transects, elevations were interpolated using topographic maps,
land-use and land cover data, and engineering judgment to determine the
aerial extent of flooding. The results of the calculations are accurate until
local topography, vegetation, or cultural development within the community
experience major changes. Table 3, “Transect Data”, provides the 10%, 2%,
1% and 0.2% annual chance stillwater elevations and the starting wave
conditions for each transect. Figure 1, “Transect Location Map”, provides
an illustration of the transect locations for Stafford County.
22
23
FIGURE 1
STAFFORD COUNTY, VA
ALL JURISDICTIONS
FEDERAL EMERGENCY MANAGEMENT AGENCY
STAFFORD COUNTY
13
14
11
23
15
0
24
4
3
2
1
8
Aquia
Creek
7
6
19
4.5
Ü
6
Miles
TRANSECT LOCATION MAP
0.75 1.5
3
Chopawamsic Creek
Potomac Creek
18
Potomac
River
5
16
12
17
10
22
9
21
QUANTICO MARINE CORPS BASE
20
FIGURE 1
Table 3 – Transect Data
Starting Stillwater Elevations
(feet NAVD 88)
Starting Wave Conditions for the 1%
Annual Chance
Significant
Wave
Height
Peak
Wave
Period
Flood Source
Transect
Coordinates
Hs (ft)
Tp (sec)
10%
Annual
Chance
2%
Annual
Chance
1%
Annual
Chance
0.2%
Annual
Chance
POTOMAC RIVER
1
N 38.500548
3.8
4.1
4.6
5.8
6.1
7.7
4.0
4.2
4.5
5.8
6.1
7.8
4.2
4.2
4.5
5.8
6.1
7.7
4.4
4.2
4.5
5.8
6.2
7.7
4.7
4.2
4.5
5.8
6.2
7.6
4.9
4.4
4.5
5.8
6.2
7.6
4.7
4.3
4.4
5.8
6.2
7.5
4.5
4.4
4.4
5.8
6.2
7.5
3.8
4.1
4.4
5.7
6.2
7.4
1.9
3.2
4.5
5.8
6.2
7.7
2.0
2.8
4.5
5.9
6.3
8.0
1.9
2.6
4.5
5.9
6.4
8.3
1.3
2.2
4.6
5.9
6.5
9.1
2.2
2.7
4.5
5.9
6.4
8.2
2.1
2.7
4.5
5.9
6.3
7.8
W -77.302374
POTOMAC RIVER
2
N 38.494625
W -77.310541
POTOMAC RIVER
3
N 38.480996
W -77.315861
POTOMAC RIVER
4
N 38.466099
W -77.323200
POTOMAC RIVER
5
N 38.455154
W -77.325197
POTOMAC RIVER
6
N 38.438256
W -77.323230
POTOMAC RIVER
7
N 38.430096
W -77.322514
POTOMAC RIVER
8
N 38.414123
W -77.317684
POTOMAC RIVER
9
N 38.396849
W -77.312393
AQUIA CREEK
10
N 38.407618
W -77.325911
AQUIA CREEK
11
N 38.414712
W -77.334460
AQUIA CREEK
12
N 38.422469
W -77.342638
AQUIA CREEK
13
N 38.438361
W -77.368509
AQUIA CREEK
14
N 38.415887
W -77.325015
AQUIA CREEK
15
N 38.350582
W -77.155448
24
Table 3 – Transect Data - continued
Starting Stillwater Elevations
(feet NAVD 88)
Starting Wave Conditions for the 1%
Annual Chance
Flood Source
AQUIA CREEK
Significant
Wave
Height
Peak
Wave
Period
Transect
Coordinates
Hs (ft)
Tp (sec)
10%
Annual
Chance
2%
Annual
Chance
1%
Annual
Chance
0.2%
Annual
Chance
16
N 38.394415
2.2
3.3
4.4
5.8
6.3
7.5
3.8
4.1
4.4
5.8
6.3
7.5
3.6
3.8
4.4
5.8
6.3
7.3
3.3
3.7
4.4
5.7
6.2
7.2
2.8
3.8
4.4
5.8
6.3
7.3
1.7
3.0
4.4
5.8
6.3
7.3
1.7
2.7
4.4
5.9
6.4
7.4
1.7
2.8
4.5
5.9
6.4
7.4
1.6
2.5
4.4
5.9
6.4
7.4
W -77.326306
POTOMAC RIVER
17
N 38.381141
W -77.314953
POTOMAC RIVER
18
N 38.373228
W -77.301093
POTOMAC RIVER
19
N 38.361245
W -77.290271
POTOMAC CREEK
20
N 38.353228
W -77.294219
POTOMAC CREEK
21
N 38.350030
W -77.312436
POTOMAC CREEK
22
N 38.350024
W -77.325998
POTOMAC CREEK
23
N 38.348719
W -77.338730
POTOMAC CREEK
24
N 38.342647
W -77.329992
Areas of coastline subject to significant wave attack are referred to as coastal
high hazard zones. The USACE has established the 3-foot breaking wave as
the criterion for identifying the limit of coastal high hazard zones (USACE,
1975). The 3-foot wave has been determined the minimum size wave
capable of causing major damage to conventional wood frame of brick
veneer structures. The one exception to the 3-foot wave criteria is where a
primary frontal dune exists. The limit the coastal high hazard area then
becomes the landward toe of the primary frontal dune or where a 3-foot or
greater breaking wave exists, whichever is most landward. The coastal high
hazard zone is depicted on the FIRM as Zone VE, where the delineated flood
hazard includes wave heights equal to or greater than 3 feet. Zone AE is
depicted on the FIRM where the delineated flood hazard includes wave heights
less than 3 feet. A depiction of a sample transect which illustrates the
relationship between the stillwater elevation, the wave crest elevation,
25
and the ground elevation profile, and how the Zones VE and AE are
mapped is shown in Figure 2, “Typical Transect Schematic”.
Post-storm field visits and laboratory tests have confirmed that wave heights as
small as 1.5 feet can cause significant damage to structures when constructed
without consideration to the coastal hazards. Additional flood hazards associated
with coastal waves include floating debris, high velocity flow, erosion, and
scour which can cause damage to Zone AE-type construction in these coastal
areas. To help community officials and property owners recognize this increased
potential for damage due to wave action in the AE zone, FEMA issued guidance
in December 2008 on identifying and mapping the 1.5-foot wave height line,
referred to as the Limit of Moderate Wave Action (LiMWA). While FEMA
does not impose floodplain management requirements based on the LiMWA,
the LiMWA is provided to help communicate the higher risk that exists in that
area. Consequently, it is important to be aware of the area between this inland
limit and the Zone VE boundary as it still poses a high risk, though not as high
of a risk as Zone VE (see Figure 2).
The AE and VE zones were divided into whole-foot elevation zones based on
the average wave crest elevation in that zone. Where the map scale did not
permit delineating zones at one foot intervals, larger increments were used.
In cases where the 1- and 0.2-percent annual chance floodplain boundaries
are close together, only the 1-percent annual chance boundary has been
shown. Small areas within the floodplain boundaries may lie above the
flood elevations, but cannot be shown due to limitations of the map scale
and/or lack of detailed topographic data.
Figure 2 - Typical Transect Schematic
26
3.4
Vertical Datum
All FIS reports and FIRMs are referenced to a specific vertical datum.
The vertical datum provides a starting point against which flood, ground,
and structure elevations can be referenced and compared. Until recently,
the standard vertical datum used for newly created or revised FIS reports
and FIRMs was the National Geodetic Vertical Datum of 1929 (NGVD
29). With the completion of the NAVD 88, many FIS reports and FIRMs
are now prepared using NAVD 88 as the referenced vertical datum.
All flood elevations shown in this FIS report and on the FIRM are now
referenced to NAVD 88. In order to perform this conversion, effective
NGVD 29 elevation values were adjusted downward by 0.83 foot.
Structure and ground elevations in the community must, therefore, be
referenced to NAVD 88. It is important to note that adjacent communities
may be referenced to NGVD 29. This may result in differences in base
flood elevations across the corporate limits between the communities.
The BFEs shown on the FIRM represent whole-foot rounded values.
For example, a BFE of 102.4 will appear as 102 on the FIRM and 102.6
will appear as 103. Therefore, users that wish to convert the elevations in
this FIS to NGVD 29 should apply the stated conversion factor(s) to
elevations shown on the Flood Profiles and supporting data tables in the
FIS report, which are shown at a minimum to the nearest 0.1 foot.
For more information on NAVD88, see FEMA publication entitled,
Converting the National Flood Insurance Program to the North American
Vertical Datum of 1988, FEMA Publication FIA-20/June 1992, or contact
the NGS on their website (http://www.ngs.noaa.gov) or at the following
address:
NGS Information Services
NOAA, N/NGS12
National Geodetic Survey
SSMC-3, #9202
1315 East-West Highway
Silver Spring, Maryland 20910-3282
4.0
FLOODPLAIN MANAGEMENT APPLICATIONS
The NFIP encourages State and local governments to adopt sound floodplain
management programs. To assist in this endeavor, each FIS report provides 1 percent
annual-chance floodplain data, which may include a combination of the following: 10-,
2-, 1-, and 0.2 percent annual chance flood elevations; delineations of the 1 percent and
0.2 percent annual chance floodplains; and a 1 percent annual-chance floodway. This
information is presented on the FIRM and in many components of the FIS report,
including Flood Profiles, and Floodway Data tables. Users should reference the data
presented in the FIS report as well as additional information that may be available at the
local community map repository before making flood elevation and/or floodplain
boundary determinations.
27
4.1
Floodplain Boundaries
To provide a national standard without regional discrimination, the 1
percent annual chance flood has been adopted by FEMA as the base flood for
floodplain management purposes. The 0.2 percent annual chance flood is
employed to indicate additional areas of flood risk in the county. For the streams
studied in detail, the 1 percent annual chance and 0.2 percent annual chance
boundaries have been determined at each cross section. The delineations are
based on the best available topographic information.
For the June 18, 1990, FIS, floodplain boundaries for Aquia Creek were
delineated using topographic maps at a scale of 2 feet and 5 feet (Bengtson,
DeBell, Elkin & Titus, Ltd., 1987).
For the March 3, 1992, FIS, floodplain boundaries for Austin Run and
Tributary 3 to Austin Run were delineated using topographic maps at
scales of 1:360 and 1:2,400, with contour intervals of 1 foot and 5 feet,
respectively (Photogrammetric Data Services of Sterling, Virginia, 1988;
Toups Corporation of McLean, Virginia, 1977).
For the February 4, 2005 revision, between cross sections, the boundaries were
interpolated using topographic maps at a scale of 1"=200' with a contour
interval of 5 feet (Stafford County, 1983 and 1988).
For the streams studied by approximate methods, the 100-year
floodplain boundaries were delineated using regional relationships,
topographic maps, floodprone area maps, and the 1980 FIS for the
unincorporated areas of Stafford County (U.S. Department of the Interior,
1977; Toups Corporation of McLean, Virginia, 1977; U.S. Department of
the Interior, Map of Flood-Prone Areas, 1966, et cetera; U.S. Department of
the Interior, 7.5-Minute Series Topographic Maps, 1966, et cetera; and
FEMA, 1980).
The 100- and 500-year floodplain boundaries are shown on the FIRM
(Exhibit 2). On this map, the 100-year floodplain boundary corresponds to
the boundary of the areas of special flood hazards (Zones A and AE), and the
500-year floodplain boundary corresponds to the boundary of areas of
moderate flood hazards. In cases where the 100- and 500-year floodplain
boundaries are close together, only the 100-year floodplain boundary has
been shown. Small areas within the floodplain boundaries may lie above
the flood elevations but cannot be shown due to limitations of the map
scale and/or lack of detailed topographic data.
This Countywide Revision
The 3-foot breaking wave is the criterion for identifying the limit of coastal high
hazard zones, with the one exception where a primary frontal dune exists. The
28
coastal high hazard zone is depicted on the FIRM as Zone VE, where the
delineated flood hazard includes wave heights equal to or greater than 3 feet. Zone
AE is depicted on the FIRM where the delineated flood hazard includes wave
heights less than 3 feet. Where the map scale did not permit delineating zones at
one foot intervals, larger increments were used. In cases where the 1- and 0.2percent annual chance floodplain boundaries are close together, only the 1percent annual chance boundary has been shown. Small areas within the
floodplain boundaries may lie above the flood elevations, but cannot be shown
due to limitations of the map scale and/or lack of detailed topographic data.
4.2 Floodways
Encroachment on floodplains, such as structures and fill, reduces flood-carrying
capacity, increases flood heights and velocities, and increases flood hazards in
areas beyond the encroachment itself. One aspect of floodplain management
involves balancing the economic gain from floodplain development against the
resulting increase in flood hazard. For purposes of the NFIP, a floodway is
used as a tool to assist local communities in this aspect of floodplain
management. Under this concept, the area of the 100-year floodplain is
divided into a floodway and a floodway fringe. The floodway is the
channel of a stream, plus any adjacent floodplain areas, that must be kept free
of encroachment so that the 100-year flood can be carried without substantial
increases in flood heights. Minimum Federal standards limit such increases to
1.0 foot, provided that hazardous velocities are not produced. The floodways
in this FIS are presented to local agencies as a minimum standard that can be
adopted directly or that can be used as a basis for additional floodway
studies.
The floodways presented in this FIS were computed for certain stream
segments on the basis of equal conveyance reduction from each side
of the floodplain. Floodway widths were computed at cross sections.
Between cross sections, the floodway boundaries were interpolated. The
results of the floodway computations are tabulated for selected cross sections
(Table 4). The computed floodways are shown on the FIRM (Exhibit 2).
In cases where the floodway and 100-year floodplain boundaries are either
close together or collinear, only the floodway boundary is shown. Portions of
the floodway for the Rappahannock River extend beyond the county
boundary.
Encroachment into areas subject to inundation by floodwaters having hazardous
velocities aggravates the risk of flood damage, and heightens potential
flood hazards by further increasing velocities. A listing of stream velocities
at selected cross sections is provided in Table 4, "Floodway Data." To
reduce the risk of property damage in areas where the stream velocities are
high, the community may wish to restrict development in areas outside the
floodway.
29
6.8
TABLE 4
32
6.8
6.8
TABLE 4
35
Near the mouths of streams studied in detail, floodway computations are
made without regard to flood elevations on the receiving water body.
Therefore, "Without Floodway" elevations presented in Table 4 for certain
downstream cross sections of Aquia Creek, Austin Run, Claiborne Run, Falls
Run, Little Falls Run, and Tributary 1 to the Rappahannock River are lower
than the regulatory flood elevations in that area, which must take into account
the 100-year flooding due to backwater from other sources.
The area between the floodway and 100-year floodplain boundaries is termed the
floodway fringe. The floodway fringe encompasses the portion of the floodplain
that could be completely obstructed without increasing the water-surface
elevation of the 100-year flood by more than 1.0 foot at any point. Typical
relationships between the floodway and floodway fringe and their significance to
floodplain development are shown in Figure 3, “Floodway Schematic.”
Figure 3 – Floodway Schematic
5.0
INSURNACE APPLICATIONS
For flood insurance rating purposes, flood insurance zone designations are assigned to
a community based on the results of the engineering analyses. The zones are as
follows:
Zone A
Zone A is the flood insurance rate zone that corresponds to the 1 percent annual chance
floodplains that are determined in the FIS by approximate methods. Because
detailed hydraulic analyses are not performed for such areas, no base flood elevations
or depths are shown within this zone.
48
Zone AE
Zone AE is the flood insurance rate zone that corresponds to the 1 percent annual
chance floodplains that are determined in the FIS by detailed methods. In most
instances, whole-foot base flood elevations derived from the detailed hydraulic
analyses are shown at selected intervals within this zone.
Zone AO
Zone AO is the flood insurance risk zone that corresponds to the areas of 1-percentannual-chance shallow flooding (usually sheet flow on sloping terrain) where average
depths are between 1 and 3 feet. Average whole-foot base flood depths derived from
the detailed hydraulic analyses are shown within this zone.
Zone VE
Zone VE is the flood insurance rate zone that corresponds to the 1 percent annual
chance coastal floodplains that have additional hazards associated with storm waves.
Whole-foot base flood elevations derived from the detailed hydraulic analyses are
shown at selected intervals within this zone.
Zone X
Zone X is the flood insurance rate zone that corresponds to areas outside the 0.2
percent annual chance floodplain, areas within the 0.2 percent annual chance
floodplain, and to areas of 1 percent annual chance flooding where average depths are
less than 1 foot, areas of 1 percent annual chance flooding where the contributing
drainage area is less than 1 square mile, and areas protected from the 1 percent annual
chance flood by levees. No base flood elevations or depths are shown within this zone.
6.0
FLOOD INSURNACE RATE MAP
The FIRM is designed for flood insurance and floodplain management applications.
For flood insurance applications, the map designates flood insurance rate zones as
described in Section 5.0 and, in the 1-percent-annual-chance floodplains that were
studied by detailed methods, shows selected whole-foot base flood elevations or
average depths. Insurance agents use the zones and base flood elevations in
conjunction with information on structures and their contents to assign premium rates
for flood insurance policies.
For floodplain management applications, the map shows by tints, screens, and
symbols, the 1- percent-annual-chance floodplain, and the locations of selected
transects sections used in the hydraulic analyses and floodway computations.
The current FIRM presents flooding information for the entire geographic area of
Stafford County. Historical data relating to the maps prepared for each community
are presented in Table 5 , “ Community Map History”.
49
TABLE 5
50
June 9, 1978
INITIAL
IDENTIFICATION
(ALL JURISDICTIONS)
STAFFORD COUNTY, VA
FEDERAL EMERGENCY MANAGEMENT AGENCY
Stafford County
(Unincorporated Areas)
COMMUNITY NAME
None
50
November 19, 1980
FIRM EFFECTIVE DATE
June 18, 1990
March 3, 1992
February 4, 2005
FIRM REVISIONS DATE
COMMUNITY MAP HISTORY
FLOOD HAZARD
BOUNDARY MAP
REVISIONS DATE
7.0
OTHER STUDIES
The USACE published a Special Flood Hazard Report on the Potomac
River and tributary streams in November 1969 (USACE, 1969). This
report gave an Intermediate Regional Tide level of 9.5 feet, which has an
approximate recurrence interval of 100 years. Subsequent conversations
with the USACE yielded a more recent tidal curve for this area that gives an
approximate 100-year tidal elevation of 7.5 feet in the study area (Guerrini,
1976). It is the policy of the USACE that the more recent curve supersedes
all previous publications.
A Floodplain Information report on the Rappahannock River was
published by the USACE in 1970 (USACE, 1970). The base flood profile
for the Rappahannock River presented in this report agrees with the·
Intermediate Regional flood profile presented in the 1970 report.
The Soil Conservation Service published a Watershed Work Plan for the
Potomac Creek watershed in 1965 (U.S. Department of Agriculture, 1965).
That plan indicated the need for the Potomac Creek Reservoir, which was
constructed later.
No floodplain boundaries or flood elevations were
presented in that report.
The USGS has published Flood-Prone Area Maps for most of the Stafford
County area (U.S. Department of the Interior, Map of Flood-Prone Areas,
1966, et cetera). These maps served, in part, as the basis for the approximate
floodplain boundary delineations in the previous study, and are therefore in
agreement.
FISs have been prepared for the adjoining counties of Prince William (FEMA, last
revised 1995; revision in progress), King George (FEMA, last revised 1990;
revision in progress), Caroline (FEMA, 2009), Culpeper (FEMA, 2007),
Fauquier (FEMA, 2008), and Spotsylvania (FEMA, 1998), and the City of
Fredericksburg (FEMA, 2007).
Because it is based on more up-to-date analyses, this FIS supersedes the
previously printed FIS for Stafford County (FEMA, 2005). This FIS also
supersedes the FBFM for Stafford County, which was published as part of
the previously printed FIS. The information on the FBFM has been added to
the FIRM accompanying this FIS.
8.0
LOCATION OF DATA
Information concerning the pertinent data used in the preparation of this study can
be obtained by contacting the office of the Federal Insurance and Mitigation
Division, FEMA Region III, One Independence Mall, Sixth Floor, 615 Chestnut
Street, Philadelphia, PA 19106-4404.
51
9.0
BIBLIOGRAPHY AND REFERENCES
Air Survey Corporation. (1983). Topographic Maps, Scale 1:2,400, Contour
Interval 5 Feet. Sterling, Virginia.
Bengtson, DeBell, Elkin & Titus, Ltd., of Woodbridge, Virginia. (March 1988).
Topographic Map of John E. Cowles property, Scale 1:1,200, Contour Interval 2
Feet. Stafford County, Virginia.
Bengtson, DeBell, Elkin & Titus, Ltd., of Woodbridge, Virginia. (May 17, 1987).
Topographic Map of Gray property, Scale 1:1,200, Contour Interval 5 Feet.
Stafford County, Virginia.
Clements, John. (1991). Flying the Colors: Virginia Facts. Dallas, Clements
Research II, Inc.
Commonwealth of Virginia. (September 1973). Virginia Uniform Statewide
Building Code, Article 8, Part C, Section 872.6.
Darling, John, (1977). Personal communication. Floodplain Management
Branch, Baltimore District, U.S. Army Corps of Engineers.
Federal Emergency Management Agency. (2007a). Atlantic Ocean and Gulf of Mexico
Update Coastal Guidelines Update. Washington, D.C.
Federal Emergency Management Agency. (2007b). Guidelines and Specifications for
Flood Hazard Mapping Partners. Washington, D.C.
Federal Emergency Management Agency. (August 2007c). Wave Height Analysis for
Flood Insurance Studies (WHAFIS), Version 4.0. Washington, D.C.
Federal Emergency Management Agency. (February 18, 1998). Flood Insurance
Study, Spotsylvania County, Virginia (Unincorporated Areas). Washington, D.C.
Federal Emergency Management Agency. (January 5, 1995). Flood Insurance
Study, Prince William County, Virginia (Unincorporated Areas). Washington, D.C.
Study, Stafford County, Virginia. Washington, D.C.
Study, Fauquier County, Virginia and Incorporated Areas. Washington, D.C.
Federal Emergency Management Agency. (December 15, 1990). Flood Insurance
Study, King George County, Virginia. Washington, D.C.
Federal Emergency Management Agency. (March 2, 2009). Flood Insurance Study,
Caroline County, Virginia and Incorporated Areas. Washington, D.C.
52
Federal Emergency Management Agency. (June 18, 2007). Flood Insurance Study,
Culpeper County, Virginia (Unincorporated Areas). Washington, D.C.
Federal Emergency Management Agency, Federal Insurance Administration.
(May 1980; Flood Insurance Rate Map effective November 19, 1980). Flood Insurance
Study, Stafford County, Virginia (Unincorporated Areas) . Washington, D.C.
Federal Emergency Management Agency. (September 19, 2007). Flood Insurance
Study, City of Fredericksburg, Virginia (Independent City) . Washington, D.C.
Guerrini, James. (September 24, 1976). Personal Communication. U.S. Army Corps
of Engineers, Baltimore District.
Internet web site, Stafford County, Virginia. (October 2000).
http://www.co.stafford.va.us/.
Internet web site, Stafford County, Virginia. (August 2013).
http://quickfacts.census.gov/qfd/states/51/51179.html.
National Academy of Sciences, Methodology for Calculating Wave Action Effects
Associated with Storm Surges. (1977).
Patterson, William, P.E. (October 26, 1976). Personal Communication. D irector,
Engineering Branch, Public Works Division, U.S. Marine Corps Development and
Education Command.
Photogrammetric Data Services of Sterling, Virginia. (April 6, 1988).
Topographic Map, Scale 1:360, Contour Interval 1 Foot.
Stafford County. (1983 and 1988). Topographic Maps, Scale 1:200, Contour Interval
5 Feet. Stafford County, Virginia.
Stafford County Planning Commission. (July 1975). Stafford County
Comprehensive Development Plan. Stafford, Virginia.
Toups Corporation of McLean, Virginia. (1977). Topographic Maps compiled from
aerial photos, scales 1:1,200 and 1:2,400, contour interval 5 feet. Stafford County,
Virginia.
U.S. Army Corps of Engineers, Baltimore District. (November 1969). Special
Flood Hazard Report, Potomac River and Tributary Streams, Stafford County,
Virginia. Baltimore, Maryland.
U.S. Army Corps of Engineers, Galveston District. (June 1975). Guidelines for
Identifying Coastal High Hazard Zones. Galveston, Texas.
U.S. Army Corps of Engineers, Hydrologic Engineering Center. (May 1991). HEC1 Flood Hydrograph Package, Version 4.0.1E. Davis, California.
U.S. Army Corps of Engineers, Hydrologic Engineering Center. (May 1974).
Floodway Determination Using Computer Program HEC-2. Training Document No.5.
Davis, California.
53
U.S. Army Corps of Engineers, Hydrologic Engineering Center. (October 1973). HEC2 Water-Surface Profiles, Generalized Computer Program. Davis, California.
U.S. Army Corps of Engineers, Hydrologic Engineering Center. (October 1973). HEC2 Water-Surface Profiles, Users Manual. Davis, California.
U.S. Army Corps of Engineers, Hydrologic Engineering Center. (September 1998
and March 1999, respectively). HEC-RAS River Analysis System, Versions 2.2.0 and
2.2.1. Davis, California.
U.S. Army Corps of Engineers, Norfolk District. (September 1970). Flood Plain
Information, Rappahannock River, Spotsylvania and Stafford Counties.
Virginia. Norfolk, Virginia.
U.S. Army Corps of Engineers, Pittsburgh District. (November 1974). Tropical
Storm Agnes, June 1972. Post Flood Report, Volumes I and II. Pittsburgh,
Pennsylvania.
U.S. Army Corps of Engineers. (2012). ERDC/CHL TR11-X. FEMA Region III
Storm Surge Study, Coastal Storm Surge Analysis: Modeling System Validation
Submission No. 2.
U.S. Department of Agriculture. Soil Conservation Service. (1987). Technical
Release No. 20, Computer Program. Project Formulation. Hydrology. Washington, D.C.
U.S. Department of Agriculture, Soil Conservation Service. (February 1974).
Soil Survey, Stafford and King George Counties. Virginia. Washington, D.C.
U.S. Department of Agriculture, Soil Conservation Service. (September 1965).
Watershed Work Plan, Potomac Creek Watershed, Stafford County, Virginia.
Washington, D.C.
U.S. Department of Agriculture, Soil Conservation Service. (1963). Guide for
Selecting Roughness Coefficient "n" Values for Channels. Washington, D.C.
G.B. Frasken (author).
U.S. Department of Commerce, National Oceanic and Atmospheric Administration,
National Weather Service. (June 1977). NOAA Technical Memorandum NWS
HYDR0-35, Five- to 60-Minute Precipitation Frequency for the Eastern and Central
United States.
U.S. Department of Commerce, Weather Bureau. (May 1961). Technical Paper No.
40. Rainfall Frequency Atlas of the United States.
U.S. Department of the Interior, Geological Survey. (2000). Water Resources
Data. Virginia, Water Year 1999, Volume 1, Surface-Water-Discharge and SurfaceWater- Quality Records, Water-Data Report VA-99-1. Washington, D.C.
U.S. Department of the Interior, Geological Survey. (1998). Water Resources Data,
Virginia, Water Year 1997, Volume 1, Surface-Water-Discharge and Surface54
Water- Quality Records, Water-Data Report VA-97-1. Washington, D.C.
U.S. Department of the Interior, Geological Survey. (March 1977). Open-File
Report, Equation for Estimating Regional Flood Depth-Frequency Relations for
Virginia. Washington, D.C. E. M. Miller (author).
U.S. Department of the Interior, Geological Survey. (July 1976). Hydrologic
Computer Program No. E660. Washington, D.C.
U.S. Department of the Interior, Geological Survey. (1968). Water Supply Paper No.
1672, Magnitude and Frequency of Floods in the United States, Part IB, North
Atlantic Slope Basins, New York to York River. Washington, D.C. Richard H. Tice.
U.S. Department of the Interior, Geological Survey. (Sommerville, Virginia,
1966; Joplin, Virginia, 1966, Photorevised 1971; Quantico, Virginia, 1965,
Photorevised 1971; Richardsville,Virginia, 1968, Photo inspected 1972; Storck,
Virginia, 1966, Photo inspected 1972; Stafford, Virginia, 1966, Photorevised 1972;
Widewater, Virginia, 1966; Salem Church, Virginia, 1966, Photorevised 1972;
Fredericksburg, Virginia, 1966, Photorevised 1971; Passapatanzy, Virginia, 1966;
Guinea, Virginia, 1966, Photorevised 1972; Rappahannock Academy, Virginia, 1969.)
7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour Interval 10 Feet.
U.S. Department of the Interior, Geological Survey. (Sommerville, Virginia, 1966;
Joplin, Virginia, 1966, Photorevised 1971; Quantico, Virginia, 1965, Photorevised
1971; Richardsville, Virginia, 1968, Photo inspected 1972; Storck, Virginia, 1966,
Photo inspected 1972; Stafford, Virginia, 1966, Photorevised 1972; Widewater,
Virginia, 1966; Salem Church, Virginia, 1966; Photorevised 1972; Fredericksburg,
Virginia, 1966, Photorevised 1971; Passapatanzy, Virginia, 1966; Guinea, Virginia,
1966, Photorevised 1972; Rappahannock Academy, Virginia, 1969.) Map of FloodProne Areas, Scale 1:24,000, Contour Interval 10 Feet.
Virginia State Board of Housing. (November 1975). 1975 Accumulative Supplement
to the Virginia Uniform Statewide Building Code, Article 8, Part C, Section 872.6.
Richmond, Virginia.
Water Resources Council. (March 1976). "Guidelines for Determining Flood Flow
Frequency, “Bulletin 17. Washington, D.C.
Weldon Cooper Center for Public Service, University of Virginia. (1998 Edition,
June 1998). Virginia's Local Economies, RADCO, Planning District Number 16,
Fredericksburg City, Caroline County, King George County, Spotsylvania
County, Stafford County. Samuel R. Kaplan (Principal Author) and John L.
Knapp (Project Director).
55

flood insurance study

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