Stratford Manor-CS 970723 Federal Emergency Management Agency
Washington, D.C. 20472
CERTIFIED MAIL IN REPLY REFER TO:
RETURN RECEIPT REQUESTED Case No.: 97-06-503P
The Honorable Candy Sheehan Community: City of Coppell, Texas
Mayor, City of Coppell Community No.: 480170
255 Parkway Boulevard Panel Affected: 0010 E
Coppell, Texas 75019 Effective Date of
This Revision:
102-I-A-C
Dear Mayor Sbeehan:
Tbis responds to a request that the Federal Emergency Management Agency (FEMA) revise the effective
Flo<xl Insurance Rate Map (FIRM) and Flood Insurance Study (FI S) report for your community in accordance
with Part 65 of the National Flood Insurance Program (NFIP) regulations. In a letter dated May 6, 1997,
Ms. Sabine Borgnet-Harris, Halff Associates, Inc., requested that FEMA revise the FIRM and FIS report to
show the effects of corrections to the effective hydraulic analysis and effective FIRM and FIS report along
Denton Creek from just downstream of the convergence to approximately 1,450 feet upstream of the
divergence of Old Denton Creek and along Old Denton Creek from its convergence with to its divergence
from Denton Creek. The corrections made as part of this revision are listed below.
· The effective hydraulic analysis shows Denton Creek and Old Denton Creek share a common
floodplain. This study is incorrect because high ground separates Denton Creek from Old Denton
Creek so that each stream has its own floodplain. As part of this revision, the effective hydraulic
analysis was separated so that each stream has its own hydraulic analysis.
· The eff~tive floodway analyses for Denton Creek and Old Denton Creek showed floodway topwidths
that were greater than the topwidths of the floodplain of the flood having a 1-percent chance of being
equaled or exceeded in any given year (base flood). The topwidths were corrected as part of this
revision.
· The eft~tive floodway analysis for Old Denton Creek showed floodway topwidths that did not match
those shown on the effective FIRM. These discrepancies were corrected.
· The cross-sectional distances shown in the effective hydraulic analyses along the revised reach for both
Denton Creek and Old Denton Creek did not match the distance shown on the effective FIRM and
Flood Profile panels 08P, 09P, and ! IP. These discrepancies were corrected.
· The configuration of Denton Creek and Old Denton Creek in the effective hydraulic analysis did not
match the configuration shown on the effective FIRM. Minor changes were made to the geometry at
Cross Sections 23800, 24400, and 24700 to correct this discrepancy.
All data required to complete our review of this request were submitted with letters from Ms. Harris. Because
this letter of Map Revision (LOMR) is being issued to correct a mapping or study analysis error, fees were
not assessed for the review.
7hr/?z
We have completed our review of the submitted data and the flood data shown on the effective FIRM and FIS
report. We have revised the FIRM and FIS report to modify the elevations and the floodplain and floodway
boundary delineations of the base flood along Denton Creek from just downstream of the convergence to
approximately 1,450 feet upstream of the divergence of Old Denton Creek and along Old Denton Creek from
its convergence with to its divergence from Denton Creek. As a result of the modifications, the base flood
elevations (BFEs) along Denton Creek increased and decreased compared to the effective BFEs; the width of
the Special Flood Hazard Area (SFHA), the area that would be inundated by the base flood, decreased
compared to the effective SFHA width; and the width of the regulatory floodway increased and decreased
compared to the effective floodway width. In addition, the BFEs along Old Denton Creek increased and
decreased compared to the effective BFEs; and the SFHA width decreased compared to the effective SFHA
width. All affected property owners were notified of the changes in BFE, SFHA width, and floodway width
in a public notice published in the Citizen's Advocate on February 14 and February 21, 1997. The
modifications are shown on the enclosed annotated copy of FIRM Panel(s) 0010 E, Profile Panel(s) 08P, 09P,
and 11P, and affected portions of the Summary of Discharges Table and Floodway Data Table. This LOMR
hereby revises the above-referenced panel(s) of the effective FIRM and the affected portions of the FIS report,
both dated April 15, 1994.
The modifications are effective as of the date shown above. The map panel(s) as listed above and as modified
by this letter will be used for all flood insurance policies and renewals issued for your community. The
changes in BFEs, when rounded to a whole foot, are equal to zero; therefore, we will not republish the BFEs.
A review of the determination made by this LOMR and any requests to alter this determination should be made
within 30 days. Any request to alter the determination must be based on scientific or technical data.
Because this LOMR will not be printed and distributed to primary users, such as local insurance agents and
mortgage lenders, your community will serve as a repository for these new data. We encourage you to
disseminate the information reflected by this LOMR throughout the community, so that interested persons,
such as property owners, local insurance agents, and mortgage lenders, may benefit from the information.
We also encourage you to prepare a related article for publication in your community's local newspaper. This
article should describe the assistance that officials of your community will give to interested persons by
providing these data and interpreting the NFIP maps.
We will not physically revise and republish the FIRM and FIS report for your community to reflect the
modifications made by this LOMR at this time. When changes to the previously cited FIRM panel(s) and FIS
report warrant physical revision and republication in the future, we will incorporate the modifications made
by this LOMR at that time.
The floodway is provided to your community as a tool to regulate floodplain development. Therefore, the
floodway modifications described in this LOMR, while acceptable to FEMA, must also be acceptable to your
community and adopted by appropriate community action, as specified in Paragraph 60.3(d) of the NFIP
regulations.
This LOMR is based on minimum floodplain management criteria established under the NFIP. Your
community is responsible for approving all floodplain development, and for ensuring all necessary permits
required by Federal or State law have been received. State, county, and community officials, based on
knowledge of local conditions and in the interest of safety, may set higher standards for construction in the
SFHA. If the State, county, or community has adopted more restrictive or comprehensive floodplain
management criteria, these criteria take precedence over the minimum NFIP criteria.
3
This determination has been made pursuant to Section 206 of the Flood Disaster Protection Act of 1973 (Public
Law 93-234) and is in accordance with the National Flood Insurance Act of 1968, as amended (Title XIII of
the Housing and Urban Developmem Act of 1968, Public Law 90-448), 42 U.S.C. 4001-4128, and 44 CFR
Part 65. Pursuant to Section 1361 of the National Flood Insurance Act of 1968, as amended, communities
participating in the NFIP are required to adopt and enforce floodplain management regulations that meet or
exceed minimum NFIP criteria. These criteria are the minimum and do not supersede any State or local
requirements of a more stringent nature. This includes adoption of the effective FIRM to which the regulations
apply and the modifications described in this LOMR. Our records show that your community has met this
requirement.
A Consultation Coordination Officer (CCO) has been designated to assist your community. The CCO will be
the primary liaison between your community and FEMA. For information regarding your CCO, please
contact:
Mr. James LeGrotte
Director, Mitigation Division
Federal Emergency Management Agency, Region VI
Federal Regional Center, Room 206
800 North Loop 288
Denton, Texas 76201-3698
(817) 898-5127
If you have any questions regarding floodplain management regulations for your community or the NFIP in
general, please contact the CCO for your community at the telephone number cited above. If you have any
technical questions regarding this LOMR, please contact Mr. Alan Johnson of our staff in Washington, DC,
either by telephone at (202) 646-3403 or by facsimile at (202) 646-4596.
Sincerely,
j ~Hazard Identification Branch
Mitigation Directorate
Enclosure(s)
cc: Mr. Kenneth M. Griffin, P.E.
Director of Public Works
City of Coppell
Ms. Sabine Borgnet-Harris
Halff Associates, Inc.
Tills AREA PROTECTED FROM THE IO0-YEAR FLOOD
BY LEVEE, DIKE, OR OTHER STRUCTURES SUBJECT KEY TO NUMBERED
TO FAILURE OR OVERTOPPING DURING LARGER' FLOODS. STREETS
~ ~ 1 CAMBRIDGE MANOR LANE
\~'~ ZONE X 2 PRINCE EDWARD LANE
~f --/ ~ ~ 3 KINGS CANYON COURT
/' L \ ~z- ' / I~ 4 CASTLE CREEK DRIVE '
o;' .~ ~ i .......... ' ,.:.~:~'.' ...' 480170 ~10 E
R~vlsed Floodw~ ~, '! ......
~ Revised 50~Y~r Floodplain ~'1 ....... .~,
TABLE 1 SUMMARY OF DISCHARGES continued
FLOODING SOURCE DRAINAGE AREA PEAK DISCHARGES (cfs)
AND LOCATION (sq. miles) 10-YEAR 50-YEAR 100-YEAR 500-YEAR
DENTON CREEK
At confluence with
Elm Fork of
Trinity River 24.23~ 10,600 15,500 17,800 36,200m
Below Cottonwood
Branch 19.45~ 13,300 18,900 21,300 36,2002
Above Cottonwood
Branch 12.52~ 9,400 13,200 14,900 36,200~
At State Route 121 10.30~ 10,000 13,800 15,600 36,200:
OLD DENTON CREEK REVISED DATA
Denton Creek * * * 4,000 *
COTTONWOOD BRANCH
At 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 3.64 '3,600 5,000 5,600 7,100
· Data not available
~Drainage area below Grapevine Lake
:Discharge for Denton Creek below Grapevine Dam controlled outflows from
Grapevine Lake
~lO0-ye~r disch~rgs for Old Dgnton Cresk u~od only in cplit floodway analyoi=.
For 10 , 50 , 100-, and 500-ygar natural con4i;ione, Old Denton Creek was
modelled au part of Denton Creek
The decrease in peak discharge with an increase in drainage area for some
streams is due to watershed shape and/or overbank storage effects.
3.2 Hydraulic Analyses
Analyses of the hydraulic characteristics of flooding from the
sources studied were carried out to provide estimates of the
elevations of floods of the selected recurrence intervals.
Cross sections were obtained from Texas State Highway Department
bridge plans, field surveys, and studies prepared by Albert H. Halff
and Associates, Inc., URS Engineers, Nathan D. Maier and Associates,
Inc., Freeze and Nichols, and Caffey and Morrison, Inc.
Locations of selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1). For st:~f.p~s _.~
for which a floodway was computed (Section 4.2), sel~
/U
REFt[CT LOMR
BASE FLOOD
FLOODING SOURCE FLOODWAY WATER SURFACE ELEVATION
WIDTH AREA VELOCITY REGULATORY FLOODWAY FLOODWAY INCREASE
CROSS SECTION DISTANCE (FEET) (SQUARE (FEET PER
FEET) SECOND) (FEET NGVD)
Denton Creek
A 21,140~ 329 5.316 3.9 452.4 452.4 453.4 1.0
J B 22,7002 263 3,182 5.2 452.7 452.7 453.6 0.9 9 ,
I
C 25,5201 ~ 571 3,677 5.8 454.7 454.7 455.~ ~.~
, o 0.7
D 29,2801 1 134 8,383 2 5 456.3 656.3 457.0
· 0.7
E 36,866~ 931 7,271 2.1 466.7 466.7 467 4
F 39,200~ 499 3,526 2.9 468.8 468.8 469.6 O. REVISED DA],
Old Denton Creek
[ ^ 900~ e5 1,075 3.7 452.9 452.e 453.0 o.e[
Cottonwood Branch
A 3,850z 356 1,780 4.1 463.7 463.7 664.5 0.8
B 6,710z 587 2,554 2.9 470.1 470.1 671.1 1.0
C 11,335z 270 2,156 3.1 487.4 487.4 488.1 0.7
D 14,7052 223 1,411 4.0 495.1 495.1 495.8 0.7
1Feet above confluence with Eim Fork of Trinity River R VISFD TO
ZFeet above convergence with Denton Creek
*Data not available RFF] FIT~OMR
DATED
FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA J'~j! "3 ..'
CITY OF COPPELL TX
(DALLAS & DENTON COS.) DENTON CREEK - OLD DENTON CREEK - COTTONWOOD BRANCH