FIS 1980 ...
..
-., ;FLOOD
A tl i AlreH/ A
1.17 ,
INSURANCE
STUDY 0 - wit � 1'
i I I I I 1 b r ,. f , ;∎ 0,.. , •
- (- I -..t, y 1 ft,^ --jet
CITY OF COPPELL,
TEXAS'
DALLAS AND DENTON COUNTIES
•
PRELIMINARY
MICHAEL BAKER, JR., INC.
NOV 0 M 1982
N cY M,N FEBRUARY 1980
+(' i i s ry a 7 G F
�Q REVISED:
\ \' �1 , = > Federal Emergency Management Agency
_ COMMUNITY NUMBER - 480170
\ 1
TABLE OF CONTENTS
1 , Page
1.0 INTRODUCTION
1.1 Purpose of Study 1
1.2 Authority and Acknowledgments
1.3 Coordination 1
2.0 AREA STUDIED 2
2.1 Scope of Study 2
2.2 Community Description 4
2.3 Principal Flood Problems 4
2.4 Flood Protection Measures 5
3.0 ENGINEERING METHODS 7
3.1 Hydrologic Analyses 7
3.2 Hydraulic Analyses 9
4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS 10
4.1 Flood Boundaries 10
4.2 Floodways 10
5.0 INSURANCE APPLICATION 15
5.1 Reach Determinations 15
5.2 Flood Hazard Factors 15
5.3 Flood Insurance Zones 16
5.4 Flood Insurance Rate Map Description 16
REVISED:
TABLE OF CONTENTS - continued
t
Page
6.0 OTHER STUDIES 18
7.0 LOCATION OF DATA 18'
8.0 BIBLIOGRAPHY AND REFERENCES 1 8
FIGURES
Figure 1- Vicinity Map 3
Figure 2- Flood heights at Moore Road 6
Figure 3- Floodway Schematic 11
•
TABLES
Table I- Summary of Discharges 8
Table 2- Floodway Data 12-14
Table 3- Flood Insurance Zone Data l 7
EXHIBITS
Flood Profiles
Elm Fork of Trinity River Panel s O1P -03P
Grapevine Creek Panels 04P -08P
Denton Creek Panels 09P -13P
Cottonwood Branch Panels 14P -17P
Flood Boundary and Floodway Map Panel 480170 0005C
PUBLISHED SEPARATELY:
Flood Insurance Rate Map Panel 480170 0005C
ii
REVISED:
FLOOD INSURANCE STUDY
CITY OF COPPELL, TEXAS
1.0 INTRODUCTION
1.1 Purpose of Study
This Flood Insurance Study investigates the existence and severity of
flood hazards in the City of Coppell, Dallas and Denton Counties,
Texas, and aids in the administration of the National Flood Insurance
Act of 1968 and the Flood Disaster Protection Act of 1973. This study
will be used to convert the City of Coppell to the regular program of
flood insurance by the Federal Emergency Management Agency (FEMA).
Local and regional planners will use this study in their efforts to
promotes sound flood plain management.
In some states or communities, flood plain management criteria or
regulations may exist that are more restrictive or comprehensive than
these on which these Federally- supported studies are based. These
criteria take precedence over the minimum Federal criteria for purposes
of regulating development in the flood plain, as set forth in the Code
of Federal Regulations at 24 CFR, 1910.1 (d). In such cases, however,
it shall be understood that the state (or other jurisdictional agency)
shall be able to explain these requirements and criteria.
1.2 Authority and Acknowledgments
The source of authority for this Flood Insurance Study is the National
Flood Insurance Act of 1968 and the Flood Disaster Protection Act of
1973.
The hydrologic and hydraulic analyses for this study were performed by
the U.S. Army Corps of Engineers, (COE), Fort Worth district, for the
Federal Insurance Administration,(FIA) under Interagency Agreement No.
(IAA)- H -7 -76, Project Order No. 21 and (IAA)- H- 10 -77, Project Order
No. 2. This study was completed in December 1978. Additional analy-
sis for this study was performed by Carter and Burgess Inc. in November
1981, and reflects information on Denton Creek and Cottonwood Branch.
Additional analysis was performed by Albert H. Halff Associates Inc.
in November 1981. Levee improvements along the Elm Fork of Trinity
River, below Ledbetter Road were incorporated in this study.
•
1.3 Coordination
Community base map selection and the identification of streams requir-
ing detailed study were done during the initial coordination meeting
held on July 12, 1976, attended by the Community Executive Officer (CEO),
the Community Coordination Office (CCO), a Texas Department of Water
REVISED:
Resources (TDWR) representative, and a COE representative. The Soil
Conservation Service (SCS), the US Geological Survey (USGS), the State
Department of Highways and Public Transportation, and the TDWR were
contacted for information related to the study. A final coordination meeting
was held on July 18, 1979, in Coppell, at which time the results of this study
were reviewed with community officials. COE and FIA officials were repre-
sented at this meeting.
2.0 AREA STUDIED
2.1 Scope of Study
This Flood Insurance covers the incorporated areas of the City of Coppell.
The area of study is shown on the Vicinity Map (Figure 1).
Detailed hydrologic and hydraulic studies were made on four streams affect-
ing the City of Coppell. It was agreed between the COE, the FIA CCO,
and the city that the detailed studies, cis shown in this report, cover the
flood hazard areas needing analysis.
All areas studied in detailed were chosen with consideration given to all
forecasted development until December 1983.
This study was prepared as part of a larger study entitled "Dallas County
- - Metro Area, Texas," covering all of Dallas County and portions of Collin,
Denton, Rockwall, and Tarrant Counties. In order to facilitate the manage-
ment, filing, and retrieval of the large amount of data produced during
' the study and to insure compatibility of data provided to adjoining communi-
ties, and to simplify future changes due to changes in city boundaries, the
following plan of study was developed.
USGS 7.5 minute quadrangle maps (Reference I) covering the entire area
to be studied were enlarged to a scale of I" = 1,000'. The upper and lower
halves of the enlarged maps were used to prepare master work maps for
the entire metro area study. As the engineering data, developed on a stream
or watershed basis, were completed, they were transferred to the appropri-
ate work map. Floodway data and flood insurance zone data tables were
also prepared as the engineering on each stream was completed. When
the master work maps contained all the data necessary for the completion
of the Coppell flood inusrance study, copies were made and used to prepare
the work maps for this report. The flood profiles were prepared in a similar
manner. Data was extracted from the previously mentioned floodway
data and flood insurance zone data tables to prepare similar tables for
this report.
2
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Although some data may be displayed on the work maps which are
outside the corporate limits of the community, this should not
present any problems in the preparation of the final insurance
maps for public distribution. In addition, as corporate boundaries
change, the data will be readily available for making alterations
in the final community maps.
2.2 Community Description
The City of Coppell lies on the Dallas- Denton County line in north
central Texas. The city is bounded on the north by unincorporated
areas of Denton County, on the east by Carrollton, and unincorporated
areas of Dallas County, on the south by Irving and Dallas, and on the
west by Grapevine. The chamber of commerce lists the 1980 population
as 3,826. Coppell is a sparsely developed residential community of
approximately 12 square miles. The city is drained by the Elm Fork
of the Trinity River and its tributaries. The Elm Fork flows in
a southerly direction, while the tributaries flow in an easterly
direction. Figure 1, the vicinity map, shows the location of Coppell
with respect to the streams which drain it. The Coppell area has
terrain characteristic of the Blackland Prairie. The topography is
gently rolling to almost level with narrow streams being well incised.
The soils in the area are mainly of the Houston Black, Haiden, and
Austin series. The native vegetation consists of bunch and short
grasses with scattered mesquite trees on the uplands and hardwood,
mainly elm, hackberry, and pecan occurring along the streams. Most
of the existing development in Coppell lies in the southwestern
part of the city. Little development exists on the flood plains in
Coppell at this time.
The climate of the study area is warm, temperate, and humid. Summers
are hot, and winters are short and mild. Extremes of temperatures
and precipitation is about 35 inches. The mean relative humidity
is 63 percent, and average temperature is 65.8 degrees F. The record
temperature extremes range from a maximum of 111 degrees F in July
1954 to a minimum of -3 degrees F in January 1930.
2.3 Principal Flood Problems
Most of the flood producing storms that occur in the Coppell area
are experienced in the spring and fall. Most of the higher floods
that have occurred in the general geographical region have resulted
from prolonged or successive storms that produce heavy rainfall
during this period; however, severe flooding can be produced by
intense local thunderstorms at any time.
Coppell has experienced few flood problems in the past, due primarily
to the fact that little development exists on the flood plains at this time.
4
• REVISED
There are two US Geological Survey stream gages in the study area. The
•
gage on the EIm Fork of the Trinity River located at Sandy Lake Road
was established in November 1943. The gage on Denton Creek located
at Highway 121 was established in October 1947 (Reference 2). Histori-
cal data for ungaged watersheds are dependent on local resident obser-
vations, news media records, published reports, and analysis of other near-
by watersheds with gage data and similar characteristics. Significant flooding
is known to have occurred within the vicinity in 1908, the early 1930's,
1942, 1947, 1949, 1957, 1962, 1963, 1964, 1965, 1969, 1973, 1974, 1976,
and 1977; however, little specific data is available.
Grapevine Creek and Cottonwood Branch undoubtedly experienced flooding
during the periods listed above, but no details are available.
According to local resident interviews, historical data for Denton Creek
begins in 1908 with a major flood which is the maximum known in the lower
basin. However, no high water marks or related stage heights have been
recorded. A flood in April 1942 reached 35.9 stage -feet (from high water
marks) at the gage and is thought to be the second largest. Grapevine
Dam, completed in 1952, regulates flows at the gage except those from
a 10.3 square mile local area between the dam and the gage.
The maximum flood of record on the EIm Fork near Coppell prior to con-
struction of the upstream reservoirs occurred in May 1908. An estimated
discharge of 145,000 cfs was experienced. The second largest discharge
of record was 90,700 cfs which occurred in April 1942. The existing up-
stream reservoirs would have reduced the 1908 and 1942 floods near Carroll-
ton from 145,000 and 90,700 cfs to 26,000 and 24,100 cfs, respectively,
based upon reservoir regulation studies. In September 1964 a flow of
- - 33,000 cfs was experienced at the Carrollton gage. This flow was generated
entirely from the uncontrolled area below the reservoirs and approaches
the magnitude of the I00 -year flood in the Coppell area (Reference 2).
It should be noted that the frequencies assigned to the historical floods
should be viewed with caution since the estimates are made by comparing
high water marks or discharge estimates obtained from historical records
with determinations made in connection with this or adjacent studies.
It is seldom possible to determine the conditions that existed at the sites
of the historical high water mark or discharge estimate. The hydrologic
determinations for this study are based on existing stream and watershed
conditions that existed at the time of the historical flood. Additionally,
the estimates may not be valid except in the immediate area of the esti-
mate.
Figure 2 shows the heights that could be reached by the respective future
floods on Grapevine Creek at Moore Road.
2.4 Flood Protection Measures
Grapevine Dam on Denton Creek and Lewisville Dam on the Elm Fork of
the Trinity River are the only major flood control projects affecting the
5
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FIGURE 2: FLOOD HEIGHT 1 1
1
This photograph shows 8 .•
future flood heights on
Grapev Creek at Moore • 1
Road. . . C •
. .,. y M • Lp O . ..
; i'500 YEAR FLOOD t 1
f '� 100 YEAR FLOOD ' ,, ,,=
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5 ,4 .:.1 1- "a+� Y -�.
6
study area. These reservoirs, providing flood control, water supply, and
recreation, were completed in 1952 and 1955, respectively. Additionally,
several short reaches of stream straightening and /or enlarging have taken •
place in connection with road construction. The City of Coppell regulates
flood plain development through a zoning ordinance.
3.0 ENGINEERING METHODS
For the flooding sources studied in detail in the community, 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 equalled or exceeded once on the average during any 10 -, 50 -, 100 -,
and 500 -year period (recurrence intervals), have been selected as having
special significance for flood plain management and for flood insurance
premium rates. These events, commonly termed the 10 -, 50 -, 100 -, and
500 -year floods, have a 10, 2, I, and 0.2 percent chance, respectively, of
being equalled or exceeded during any year. Although the recurrence inter-
val 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 one year are considered. For example, the risk of having
a flood which equals or exceeds the 100 -year flood (one percent chance
of annual occurrence) in any 50 year period is about 40 percent (four in
10), and for any 90 year period, the risk increases to about 60 percent (six
in 10). The analyses reported here 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.
3.1 Hydrologic Analyses
Hydrologic analyses were carried out to establish the peak discharge- frequency
relationships for floods of the selected recurrence intervals for each stream
studied in detail affecting the community.
The hydrologic procedures used in developing discharge- frequency curves
for the East Fork of the Trinity River are based on the method recommended
in the Water Resources Council Bulletin No. 17, "Guidelines for Determining
Flow Frequency" (Reference 3). Historical discharge - frequency curves
were developed at six gages in the Trinity River basin near Dallas. The
final discharge - frequency curve for each location is a composite curve
using observed discharge data with consideration given to rare hypotheti-
cal floods. The 100- and 500 -year events are based on the values reflected
by the composite or final curves plotted on log probability paper. The
only stream gage on the Elm Fork of the Trinity River is located at the
Sandy Lake Road bridge just east of Coppell in Carrollton, Texas. Each
7
of the remaining streams were divided into subareas, and synthetic unit
and flood hydrographs were developed at selected locations. National
Weather Service Technical Paper Number 40 (Reference 4) was used in
developing the 10 -, 50 -, and I00 -year storms. The 500 -year storm was
based on extrapolated data. Frequency peak discharges at selected loca-
tions were computed. Additionally, numerous headwater areas of Tess than
1 square mile were modeled using the rational method, where Q = CIA.
The variables in this method are defined as follows: Q is the peak discharge
in cfs, C is a runoff coefficient, 1 is the rainfall intensity in inches per
hour for the watershed time of concentration, and A is the drainage area
in acres. Drainage area peak discharge relationships for streams in the
study area are shown in Table I, "Summary of Discharges." The decrease
in peak discharge with an increase in drainage area for some streams is
due to watershed shape and /or overbank storage effects.
TABLE 1 - SUMMARY OF DISCHARGES
DRAINAGE AREA PEAK DISCHARGES (cfs)
FLOODING SOURCE AND LOCATION (sq. miles) 10 -YEAR 50 -YEAR 100 -YEAR 500 -YEAR
ELM FORK OF TRINITY RIVER
USGS gage located at
Sandy Lake Road 104 4/ 16,400 30,200 37,400 65,000
GRAPEVINE CREEK
Confluence with Elm Fork 11.48 3/ 5,900 8,600 9,700 12,700
At South Fork 10.55 6,900 9,700 11,800 15,200
At Moore Road 9.65 7,500 10,500 11,800 15,100
Below Stream 7F1 8.14 7,600 10,600 11,900 15,100
Above Stream 7F1 7.17 6,700 9,400 10,500 13,400
At intersection with
extension of Cotton Road 5.95 7,300 10,00 11,200 14,200
At Radio Road 3.68 5,100 7,000 7,900 9,900
DENTON CREEK
Confluence with Elm Fork 24.23 1/ 10,600 15,500 17,800 36,200 2/
Below Cottonwood Branch 19.45 T/ 13,300 18,900 21,300 36,200 2/
Above Cottonwood Branch 12.52 1/ 9,400 13,200 14,900 36,200 2/
At Highway 121 10.30 1/ 10,000 13,800 15,600 36,200 2/
COTTONWOOD BRANCH
Confluence with Denton
Creek 6.93 4,500 6,400 7,300 9,400
At Sandy Lake Road 5.69 4,200 5,900 6,700 8,600
At State Road 4.69 3,600 5,100 5,700 7,300
At Bethel Road 3/ 3.64 3,600 5,000 6,200 7,800
1/ Drainage area below Grapevine Lake.
2/ Discharge for Denton Creek below Grapevine dam controlled outflows from
Grapevine Lake.
8
3/ Outside corporate limits.
• 4/ Drainage area below Grapevine Lake and Lewisville Lake.
3.2 Flydraulic Analyses
Analyses of the hydraulic characteristics of the flooding sources
studies in detail in the community were carried out to provide
estimates of the elevations of floods of the selected recurrence
intervals along each of these flood sources. Water- surface eleva-
tions of floods of the selected recurrence intervals for each of
the smaller streams were computed through use of the COE HEC -2
step- backwater computer program (Reference 5). Water- surface
elevations for the Trinity River were computed using the LRD -I
(Modified) water - surface profile computer program (Reference 6).
Cross sections for the backwater analyses of the streams studied
were filed surveyed and were located at close intervals above or
below bridges and culverts in order to compute the significant
backwater effects of these structures. Channel roughness factors
(Manning's "n ") for these computations were assigned on the basis
of field inspections of flood plain areas and on previous studies
by the COE. Following is a list of the "n" value ranges.
Stream Name Channel Overbank
Elm Fork of Trinity River .030 -.055 .035 -.085
Grapevine Creek .045 -.055 .060 -.080
Denton Creek .045 -.060 .050 -.060
Cottonwood Branch .050 -.050 .060 -.070
Flood profiles were drawn showing computed water - surface elevations
to an accuracy of 0.1 foot for floods of the selected recurrence
intervals. The computer backwater models for the Elm Fork of the
Trinity River were compared to previous studies for verification
of results. Starting water- surface elevations for the Elm Fork of
the Trinity River and Denton Creek were based on coincident con-
ditions. The remaining streams were based on slope -area determina-
tions. All elevations are measured from National Geodetic Vertical
Datum of 1929 (NGVD). Elevation reference marks used in the study
are shown and described on the maps.
For study purposes, it was assumed that no clogging would occur
and that all bridge structures would stand intact. Significant
changes in this premise, imposed by differing conditions of a future
flood, could alter the estimated flood elevations and flood limits
shown on profiles and maps. Locations of selected cross sections
used in the hydraulic analyses are shown on the Flood Profiles.
For stream segments for which a floodway is computed (Section 4.2),
selected cross section locations are also shown on the Flood
Boundary and Floodway Map.
9
REVISED.
LOQDELAIN_MANAGEMENT APPLICATI.ONS
I � The National Flood Insurance Program encourages state and local governments
to adopt sound flood plain management programs. Therefore, each Flood In-
surance Study includes a flood boundary map designed to assist communities
in developing sound flood plain management measures.
1
4.1 Flood Boundaries
In order to provide a national standard without regional discrimina-
tion, the 100 -year flood has been adopted by FEMA as the base flood
for purposes of flood plain management measures. The 500 -year flood
is employed to indicate additional areas of flood risk in the commun-
ity.
For each stream studied in detail, the boundaries of the 100 -year and
the 500 -year flood have been delineated using the flood elevations
determined at each cross section. Between cross sections, the i
boundaries were extrapolated using available topographic maps with
a contour interval of 10 feet (Reference A topographic map,
contour interval 2 feet, supplied by Carter and Burgess Incorporated
(Reference 7), was available for Denton Creek. In cases where the
100 -year and the 500 -year flood boundaries are close together, only
the 100 -year boundary has been shown. Small areas within the flood
• boundaries may lie above the flood elevations and therefore not be
subject to flooding owing to limitations of the map scale, such
areas argot slrowrf.
• To assist users of the flood insurance report data in locating the '.
actual boundaries of the base flood or for determining the elevation
of specific sites or structures in relation to the base flood, eleva-
tion reference marks are shown on the maps. These reference marks
include existing US Coast and Geodetic Survey bench marks, as well
as bench marks established for the current study.
Flood boundaries are indicated on the Flood Insurance Rate Map. On .
this map, the 100 -year flood boundary corresponds to the boundary of
the areas of special flood hazards; and the 500 -year flood boundary;
corresponds to the boundary of areas of moderate flood hazards (Zone B).
1
4.2 Floodways 1
Encroachment on flood plains, such as artificial fill, reduces the
flood- carrying capacity, increases the flood heights of streams, and
increases flood hazards in areas beyond the encroachment itself. One
aspect of flood plain management involves balancing the economic gain
from flood plain developmentagainst the resulting increase in flood
hazard. For purposes of the National Flood Insurance Program, the
concept of a floodway is used as a tool to assist local communities
in this aspect of flood plain management. Under this concept, the
area of the 100 -year flood is divided into a floodway and a floodway
fringe.--The-floodway is —the - channel- of - a- stream - plus -any. adjacent_
flood plain areas that must be kept free of encrachment in order that
the 100 -year flood may be carried without substantial increases in
flood heights. Minimum standards of FEMA limit such increases in
flood heights to 1.0 foot, provided that hazardous velocities are not
produced. 10
REVISED:
The floodway proposed for this study was computed on the basis of
equal conveyance reduction from each side of the flood plain. The
results of these computations are tabulated at selected field cross
sections for each stream segment for which a floodway is computed
(Table 2). As shown on the Flood Boundary and Floodway Map, the
floodway boundaries were determined at cross sections; between cross
sections the boundaries were extrapolated.
The floodways in this report are presented to local agencies as minimum
standards that can be adopted or that can be used as a basis for additional
studies. The area between the floodway and the boundary of the 100 -year
flood is termed the floodway fringe. The - floodway fringe thus encompasses
the portion of the flood plain that could be completely obstructed without
increasing the water - surface elevation of the 100 -year flood more than
1.0 foot at any point. Typical relationships between the floodway and the
floodway fringe and their significance to flood plain development are shown
in Figure 3.
•
I . 100 YEAR FLOOD PLAIN
1 FLOODWAY FLOODWAY
-
FRINGE FLOOOWAY �•w FRINOE
STREAM ••
CHANNEL
FLOOD ELEVATION WHEN
CONFINED WITHIN FLOODWAY
ENCROACHMENT ENCROACHMENT
4URCHARGE•
A
AMA OF FLOOD PLAIN THAT COULD FLOOD ELEVATION
BE USED FOR DEVELOPMENT BY ` BEFORE ENCROACHMENT
RAISING GROUND ON FLOOD PLAIN
LINE A - B IS THE FLOOD ELEVATION BEFORE ENCROACHMENT
LINE C • 0 IS THE FLOOD ELEVATION AFTER ENCROACHMENT
'SURCHARGE NOT TO EXCEED 1.0 FOOT OR LESSER AMOUNT IF SPECIFIED BY STATE.
FLOODWAY SCHEMATIC Figure 3
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17
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3
N 01 tnN N r r r N N N M z
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A w L O
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to 3 ;"' w O
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REVISED: TABLE 2
5.0 INSURANCE APPLICATION
In order to establish actuarial insurance rates, FEMA has developed a process
to transform the data from the engineering study into flood insurance criteria.
This process includes the determination of reaches, Flood Hazard Factors
(FHFs), and flood insurance zone designations for each significant flooding
source affecting the City of Coppell.
5.1 Reach Determinations
Reaches are defined as lengths of watercourses having relatively the
same flood hazard, based on the average weighted difference in water -
surface elevations between the 10- and 100 -year floods. This difference
does not have a variation greater than that indicated in the following
table for more than 20 percent of the reach.
Average Difference Between
10- and I00 -Year Floods Variation
Less than 2 feet 0.5 foot
2 to 7 feet 1.0 foot
Eight reaches meeting the above criteria were required for the flooding
sources affecting the City of Coppell. The location of reaches are shown
on the Flood Profiles.
5.2 Flood Hazard Factors (FHFs)
The Flood Hazard Factor is used to correlate flood information with
insurance rate tables. Correlations between property damage from
floods and their assigned FHFs are used to set actuarial insurance premium
rate tables based on FHFs from 005 to 200.
The FHF for a reach is the average weighted difference between the
10- and 100 -year flood water - surface elevations expressed to the nearest
one -half foot, and shown as a three -digit code. For example, if the diff-
erence between the water - surface elevations of the 10- and 100 -year
floods is 0.7 foot, the FHF is 005; if the difference is 1.4 feet, the FHF
is 015; if the difference is 5.0 feet, the FHF is 050. When the differ-
ence between the 10- and 100 -year flood water- surface elevations is
greater than 10.0 feet, the accuracy for the FHF is to the nearest foot.
j5
REVISED:
5.3 Flood Insurance Zones
After the determination of reaches and their respective FHFs, the entire
• incorporated area of Coppell was divided into zones, each having a specific
flood potential or hazard. Each zone was assigned one of the following
flood insurance zone designations:
Zone A: Special flood hazard areas inundated
by the 100 -year flood, determined
by approximate methods; no base flood
elevations or FHF determined.
Zone A2, A3,
A7
A4, A5, Special flood hazard areas inundated
by the 100 -year flood, determined
by detailed methods; base flood ele-
vations are shown and zones subdivided
according to FHF.
Zone B: Areas between the Special Flood Hazard
Area and the limits of the 500 -year
flood; areas that are protected from
the 100 -year or 500 -year flood by
dike, levee, or other water control
structure; areas subject to certain
types of 100 -year shallow flooding
where depths are Tess than 1.0 foot;
and areas subject to 100 -year flooding
from sources with drainage areas less
than I square mile. Zone B is subdi-
vided.
Zone C: Areas of minimal flooding.
Table 3, Flood Insurance Zone Data, summarizes the flood differences,
FHF, flood insurance zones, and base flood for each flooding source in
the community.
5.4 Flood Insurance Rate Map Description
The Flood Insurance Rate Map for the City of Coppell is, for insurance
purposes, the principal result of the Flood Insurance Study. This map
(published separately) contains the official delineation of flood insurance
zones and base flood elevation lines. Base flood elevation lines show
the locations of the expected whole -foot water - surface elevations of
the base (I00 -year) flood. This map is developed in accordance with
the latest flood insurance map preparation guidelines published by
FEMA.
16
REVISED:
O. 0 0 � a a s b M. (0 no W ! i
I-I CD X ca
H Z CC
W W to to N to W N In CU to _
tf)
a W 1 1 1 1 1 1 1 1 W V
W O O O O a N O N II- .... Q
•r r ./....r. •r r •r •r Q > CC
L L L L L L L L Q CO
W Q C
21C tr CD
O C7
Z ¢ Q as a aQQ 4.1
1%.1 1 z
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w ° z ' 0
l
in CC I=v
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0 �o 0 0 oU)L) A N 1.- Y
N U M N r-1N r, r+Nr -1 z Z = W
4. a 00 00 O 000 1.1,1
k.
_ 4.) O 0" C-7
a 0 w go (tai.. 0 0
N n ; �-, NCO 1-0 0 I-. toO 0 be Z
U O O N • - I 0 r-1 r-1 Co .--I r� 0 W
s N ++ ++ + + ++ r, °[ Op
tT IL
wn
H>" W CnID Mtn M M ^� W W Cn
• Z0 00 00 O 000 N
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F a
a t--I
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4 .3 v
a W d W •::1 •-• O 01 M 0 LC) to J
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Er 0 t 1 1 1 1 1 1 1 a)
v ry a U
in z
w
a (.9
W LC) to in to co 1.11111 Lo
Z CD 0 0 0 0 0 0 0 0 0 0 0 0 i... E
a o0 00 O 000 ro Z N
a g J C.)
w J z
in Q 1.1.1 O
z z Z
W 44 CL. o
W " a O
u _c x - c 'a U V
O
cn L a L v z z
0) L Y 07 U w LL Q
C
cd CC
CD O Cei
H CC • N a) •-1 N L .-•i 0 r•+ N M 0 W
t0
QO L >..C..0 r.0 - U .0 3.C to U.1
Q
O 0 4." O U > U U C U C U U c_)
H J — G
.] L •r b b a) RS (0 0 (0 0 b R) < (44.) C
I,, C a) a) a a) C) 4) a) 4-) a) C) a) ,� C V
E ..- CC Z' roCCC4 CCC +- IY1:4 0
W F- C7 0 U
- W
.-1
U.
REVISED: TABLE 3
• 1 1 • 1 ES
A report entitled "Partial Hydrologic and Hydraulic Data foh Flood Plain
Delineation, Grapevine Creek, Cit,Y of Coppell, Texas," was published in
November 1976 (Reference 8). That report covers a reach of Grapevine
Creek located between Moore Road arid Denton Tap Road.
The 100 -year frequency flood elevations and discharges developed in this
report are based on a fully developed watershed and as would be expected
are higher than those developed for the Coppell flood insurance study.
Flood insurance studies for the adjacent communities of Carrollton, Grape
vine, and Irving, Texas (References 9 -11) were prepared concurrently with
this study and are in total agreement. Dallas County (Reference 12) was
prepared before levee improvementdata along the Elm Fork of Trinity River
was available and does not match this study. No published Flood Insur-
ance Study has been prepared for the City of Dallas or Tarrant County.
This study is authorative for thepurposes of the Flood Insurance Program,
and the data presented here either supersede or are compatible with previous
determinations.
7.0 LOCATION OF DATA
Information concerning the pertinent data used in preparation of this
study can be obtained by contacting the Natural and Technological Hazards
Division, Federal Emergency Management Agency, Federal Center, Denton,
Texas 76201
•
8.0 BIBLIOGRAPHY AND REFERENCES
1. US Geological Survey 7 1/2 Minute Quadrangle Maps: Carollton, Texas,
dated 1959 and photorevised In 1968 and 1973; Grapevine, Texas, dated
1959 and photorevised in 1968 and 1973.
2. US Geolgoical Survey, Stream Gaging Records.
3. Water Resources Council Bulletin No. 17, Guidelines for Determining
Flow Frequency, March, 1976.
4. National Weather Service, Technical Paper er Number 40, Rainfall Fre-
quency Atlas of the United States, May, 1961.
5. Corps of Engineers, HEC -2, Water Surface Profiles, Hydrologic Engineer -
ing Center, Davis California; November, 1976 updated August, 1977.
6. Corps of Engineers, LRD -1 (Modified) Water Surface Profiles, Little;
Rock District, Corps of Engineers, modified by the Fort Worth Dis-
trict, Corps of Engineers.
7. Carter and Burgess Incorporated, topographic map, Univest, Coppell,
Texas, 2' contour interval, Scale 1:2400 July 10, 1981.
. I i
-$- REVISED:
8. Albert H. Halff Associates, I Engineers, Partia Hy•ro oqic an•
Hydraulic Data for Flood Plain Delineation, Grapevine Creek, City of
Coppell, Texas, for North Lake Woodlands Addition, Furguson and Deere,
Inc., November 18, 1978.
9. Federal Emergency Management, Agency, Flood Insurance Study, City of
Carrollton, Texas, January, 980. (Revision in progress)
10. Flood Insurance Study, City of Grapevine, Texas, May, 1982.
� I
11. Flood Insurance Study, City of Irving, Texas, May, 1980. 1
(Revision in Progress)
12. Flood Insurance Study, Dallas County, Texas, Unincorporated
Areas, January, 1982.
Albert H. Halff Associates, nc., Engineers, Irving Flood Control.
District -- Section III, Irvine, Texas. November, 1981.
i I
_ 16 _ REVISED: