ST9301A-CS 950525
Federal Emergency Management Agency
2 5 1995
CERTIFIED MAIL IN REPLY REFER TO:
RETURN RECEIPT REQUESTED Case No.: 95-06-096R
The Honorable Tom Morton Community: City of Coppell, Texas
Mayor, City of Coppell Community No.: 480170
P.O. Box 478
Coppell, Texas 75019 104
Dear Mayor Morton:
This is in response to a letter dated April 11, 1995, from Mr. Walter E. Skipwith, P.E., Vice President,
Halff Associates, Inc., to the Federal Emergency Management Agency (FEMA) regarding the effective
Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FIS) report for the City of Coppell,
Texas. With his letter, Mr. Skipwith provided additional information to support a December 20, 1994,
request for a Conditional Letter of Map Revision (CLOMR) from Ms. C. Jean Hansen, P.E., Project
Manager, Halff Associates, Inc. Ms. Hansen requested that FEMA evaluate the effects that a proposed
Sandy Lake Road bridge replacement, raising of the bridge approach embankment, and construction of
a swale/pond downstream of Sandy Lake Road along the Elm Fork of the Trinity River would have on
the effective FIRM and FIS report.
All data required by FEMA to evaluate this request were submitted by Ms. Hansen with her letters dated
December 20, 1994, and January 27, 1995; with letters dated March 27, March 29, and April 11, 1995,
from Mr. Skipwith; and with a letter dated February 15, 1995, from Mr. Allen Bud Beene, P.E.,
Director of Public Works, Dallas County.
In a letter dated March 27, 1995, Mr. Skipwith certified that the project is a flood-control project that
is sponsored by a Federal, State, or local government, is for public benefit, and is intended for flood loss
reduction to insurable structures in identified flood hazard areas that were in existence prior to
commencement of the flood-control project. Therefore, in accordance with Section 72.5 of the National
Flood Insurance Program (NFIP) regulations, the fees associated with our review of this CLOMR have
been waived.
We have reviewed the data submitted and the flood data used to prepare the effective FIRM for the City
of Coppell, Texas. The submitted existing conditions HEC-2 hydraulic computer model, dated June 23,
1994, based on updated topographic information, was used as the base conditions model in our review
of the proposed conditions model for this CLOMR request. We believe that if the proposed project is
constructed as described in the report entitled "Request for Conditional Letter of Map Revision on the
Elm Fork of the Trinity River - Sandy Lake Road Bridge Hydraulic Study," and as shown on Figure 8,
"Proposed Sandy Lake Road Bridge Section," of this report, dated June 1994, and prepared by Halff
Associates, Inc., a revision to the FIRM would be warranted. CLOMRs for this project have been issued
on this date for the Cities of Dallas and Carrollton, Texas.
2
As a result of the proposed bridge replacement project, new topographic information, and a more detailed
hydraulic analysis, the base flood elevations (BFEs) will be revised from just upstream of Beltline Road
to the confluence with Denton Creek along the Elm Fork of the Trinity River, and from the confluence
with the Elm Fork of the Trinity River to approximately 15,000 feet upstream along Demon Creek. (The
base flood is defined as a flood having a 1-percem probability of being equaled or exceeded in any given
year.) The BFEs will increase in some areas and decrease in other areas. The increases in BFEs are due
to new topographic information and a more detailed hydraulic analysis. The maximum increase, 0.8 foot,
will occur approximately 1,300 feet upstream of Beltline Road. Decreases in BFEs will occur from just
downstream to just upstream of Sandy Lake Road. The post-project BFEs will decrease throughout the
revised reach compared to the existing (pre-project) BFEs. The maximum decrease is 1.4 feet,
immediately upstream of the proposed bridge. The floodway will be reduced in the reach from Beltline
Road to approximately 6,000 feet upstream of Sandy Lake Road. The Special Flood Hazard Area will
be unchanged as a result of this project.
Upon completion of the project, your community may submit the data listed below and request that we
make a final determination on revising the effective FIS report and FIRM.
/ · A floodway designation with backup calculations for Demon Creek from approximately~x
' 3,000 feet upstream to approximately 13,000 feet upstream of the confluence with the x~
/ Elm Fork of the Trinity River
~i · As-built plans, certified by a registered professional engineer, of all proposed project~
~ elements
/
· Copy of the public notice distributed by the community stating the community's intent/
property owners and affected adjacent jurisdictions
to revise the floodway, or a statement by the community that it has notified all affected/
After receiving appropriate documentation to show that the project has been completed, FEMA will
initiate a revision to the FIRM and FIS report. Because the BFEs would change as a result of this
project, a 90-day appeal period would be initiated, during which community officials and interested
persons may appeal the revised BFEs based on scientific or technical data.
Because the existing floodway will need to be modified as part of the revision, we would require a letter
from you stating that the community would adopt and enforce the modified floodway. If the State of
Texas has jurisdiction over either the floodway or its adoption by your community, we would need a copy
of your letter to the appropriate State agency notifying it of the floodway modification and a copy of a
letter from that agency stating its approval of the modification.
The basis of this CLOMR is, in whole or in part, a proposed channel-modification and bridge project.
Paragraph 60.3(b)(7) of the NFIP regulations requires that communities "assure that the flood-carrying
capacity within the altered or relocated portion of any watercourse is maintained." This provision is
fincorporated into your community's existing floodplain management regulations. Consequently, your
community must agree to accept responsibility for the maintenance of the modified channel before
allowing its construction.
This response to Ms. Hansen's request is based on minimum floodplain management criteria established
under the NFIP. Your community is responsible for approving all proposed floodplain development,
including this request, and for assuring that the necessary permits required by Federal or State law have
been received. State and community officials, based on knowledge of local conditions and in the interest
of human safety, may set higher standards for construction or may limit development in floodplain areas.
If the State of Texas or your community has adopted more restrictive or comprehensive floodplain
management criteria, those criteria take precedence over the minimum NFIP requirements.
If you have any questions regarding floodplain management regulations for your community or the NFIP
in general, please contact the Consultation Coordination Officer (CCO) for your community. Information
on the CCO for your community may be obtained by contacting the Director, Mitigation Division of
FEMA in Denton, Texas, at (817) 898-5127. If you have any technical questions regarding this
CLOMR, 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, ·
~ Michael K.)e~,i ~j~.~"~.E., Chief
Hazard Id.__ lcation Branch
MitigationLIJ~ 'ectorate
Enclosures
cc: Mr. Walter E. Skipwith, P.E.
Vice President
Halff Associates, Inc.
Mr. Kenneth M. Griffin, P.E.
Assistant City Manager/Director
of Public Works
City of Coppell
Mr. Allen Bud Beene, P.E.
Director of Public Works
Dallas County