FIRM-921125Federal Emergency Management Agency
Washington, D.C. 20472
NOV 2 5
1992
Mr. Timothy M. Tumulty, P.E. Case No.: 6 -91 -169
Carrollton City Engineer Community: City of Carrollton,
P.O. Box 110535 Dallas, Denton, and
Carrollton, Texas 75011-0535 Collin Counties, Texas
Community No.: 480167
Dear Mr. Tumulty:
This is in response to your July 23, 1992, letter of appeal to the April 17,
1992, preliminary Flood Insurance Study (FIS) and Flood Insurance Rate Map
(FIRM) for the City of Carrollton, Texas. With your letter, you forwarded a
July 13, 1992, letter from Mr. William L. Wallace, P.E., Vice President of
Nathan D. Maier (NDM), Consulting'Engineers, Inc., in which he expressed his
concern with the following three issues: the U.S. Army Corps of Engineers
(USAGE) Reconnaissance Study for the Elm Fork Trinity River; the 100 -year
floodplain and floodway for the Elm Fork Trinity River; and an existing
conditions HEC -2 hydraulic model for Stream 6D5.
The first concern questioned the use of the USACE Reconnaissance Study to
revise flood hazards for the Elm Fork Trinity River. In his July 13, 1992,
letter, Mr. Wallace expressed doubt that the USACE Reconnaissance Study was
reviewed in sufficient detail for use as a FIS model. The HEC -2 hydraulic
model for the Elm Fork Trinity River that was used in the preparation of the
April 17, 1992, preliminary FIRM for the City of Carrollton was the same model
used to prepare the December 18, 1991, preliminary FIRM for the contiguous
City of Coppell. This model, which underwent technical review during the
preparation of the preliminary FIRM for the City of Coppell, used the 1986
USACE Elm Fork Trinity River HEC -2 model as a base and incorporated the
changes described below to better reflect existing conditions.
o This model utilized revised discharges contained in the March 1990
technical report prepared by the Fort Worth District USACE,
entitled Reconnaissance Report Upper Trinity River Basin, Texas.
We received a December 13, 1990, letter from Mr. Jimmy D. Baggett,
P.E., Chief of Hydrology and Hydraulics for the Fort Worth Dis-
trict USACE, stating that the revised discharges contained in this
report were appropriate for use in the preparation of the FIS for
the City of Coppell.
o The Elm Fork Trinity River model reflected three additional field -
surveyed cross sections not reflected in the 1986 USACE model and
two cross sections revised to correct errors in the 1986 USACE
model. This revised cross - sectional information was obtained from
the existing conditions HEC -2 model submitted in support of a
July 24, 1990, conditional Letter of Map Revision request for the
City of Carrollton for a proposed ring levee construction and
swale excavation. This model was prepared by NDM.
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o The floodway for the Elm Fork Trinity River was revised just
upstream of the St. Louis and Southwestern Railroad at the HRWS
tract to better reflect ineffective flow areas. This information
was taken from a HEC -2 model prepared by NDM that was submitted
with a July 3, 1990, letter from Ms. M. Shohre Daneshmand, City of
Coppell Floodplain Administrator.
o The revised HEC -2 model for the Elm Fork Trinity River reflected
the completion of the new bridge at Beltline Road.
Therefore, the revised HEC -2 model for the Elm Fork Trinity River more
accurately depicted existing conditions than the 1986 USACE model and, thus,
was used to revise the City of Coppell FIRM and, subsequently, the City of
Carrollton FIRM. In addition, our files indicate that NDM was informed of
these changes to the model for the Elm Fork Trinity River in letters from the
Federal Emergency Management Agency (FEMA) dated September 18 and November 30,
1990, to the Honorable Mark Wolfe, Mayor of the City of Coppell. NDM was also
sent a copy of the December 18, 1991, preliminary revised FIRM for the City of
Coppell reflecting these changes.
The second concern questioned the 100 -year floodplain and floodway delineation
/ for the Elm Fork Trinity River. Mr. Wallace indicated that the floodway for
the Elm Fork Trinity River should be revised upstream of Beltline Road and
upstream and downstream of Sandy Lake Road. In order to revise the floodway
upstream of Beltline Road, a revised HEC -2 hydraulic model with the revised
floodway should be submitted. The model should include any other floodway
changes made along the Elm Fork Trinity River. The data supporting a floodway
revision upstream and downstream of Sandy Lake Road, which were prepared by
Don A. Tipton, Inc., in a report entitled, Elm Fork Trinity River. City of
Carrollton Dallas County Texas Floodway Study. Southwest Landscape Nursery,
are currently under review by our Technical Evaluation Contractor (TEC).
�j Additional data necessary to complete their review were requested in a letter
` from FEMA dated September 3, 1992. If the requested data are received within
&30 days of the date of this letter, then they will be incorporated into a
\/l revised preliminary FIS and FIRM for the City of Carrollton.
✓� ���The third concern questioned the 100 -year water- surface elevations for Stream
6D5. This concern is being considered as an appeal. A revised model is being
prepared by our TEC for Stream 6D5 to incorporate the existing conditions
HEC -2 hydraulic model from the Nelson Corporation report entitled, Addendum to
Hydrology and Hydraulic Study. Hutton Branch Tributary Stream 6D5. Wellington
Run Development, Carrollton, Texas, dated January 1992. A revised preliminary
FIS and FIRM will be prepared incorporating the results of this revised model.
Please submit the requested data, to the Federal Emergency Management Agency,
Federal Insurance Administration, Office of Risk Assessment, 500 C Street SW,
Room 422, Washington, D.C. 20472, to my attention. If additional data
supporting a revision to the Elm Fork Trinity River are not received within 30
days of the date of this letter, a revised preliminary FIS and FIRM will be
issued to include the revised model for Stream 6D5, which will resolve this
appeal.
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Should you have any questions regarding this matter, please do not hesitate to
contact the Chief, Natural and Technological Hazards Division of FEMA in
Denton, Texas, at (817) 898 -5127, or Matthew B. Miller of our Headquarters
staff in Washington, D.C., at (202) 646 -3461, or by facsimile at (202) 646-
3445.
Sincerely,
U-� �j , '-S2 -
William R. Locke
Chief, Risk Studies Division
Federal Insurance Administration
cc: Mr. William L. Wallace, P.E.
State Coordinator