Park, Peter-CS 961008 CONSULTING ENGINEERS, INC.
October 8, 1996
Mr. Walter E. Skipwith, P.E.
Project Manager and Vice-President
Halff Associates
8616 Northwest Plaza Drive
Dallas, Texas 75225
Subject: Review of Floodplain Study Report
18.9 acre Sandy Lake Road Property
City of Coppell, Texas
Dear Mr. Skipwith:
We have received a copy of your review letter dated September 10, 1996, and the related
notes, by way of facsimile transmittal from the City of Coppell (City). However, we have
not seen the two !1" X 17" maps referenced in your review letter.
All that you have been furnished by the City is a copy of the report for a Conditional Letter
of Map Revision (CLOMR) Request, based on our telephone conversation a couple of
weeks ago. Yet, there is another report for the purpose of Application for a Corridor
Development Certificate (CDC) that Nathan D. Maier Consulting Engineers, Inc. (NDMCE)
submitted to the CiW at the same time as the CLOMR Report. Most of your review
comments are addressed in the CDC Report and we are hereby furnishing you with a copy.
Following are brief responses to the items in your review letter; the notes accompanying
your review letter are not addressed below. The item, numbers correspond to those in your
review letter for ease of reference.
(1) This item is thoroughly addressed in the CDC Report.
(2) This item is thoroughly addressed in the CDC Report.
(3) The overall site has been disturbed by previous non-related activities, such as the recent
laying of a large pipeline along Sandy Lake Road. Also, the reclamation plan calls for the
t,4,,o existing ponds on the site and the stream bed of Denton Creek below the normal water
level to remain in existing conditions. Thus, NDMCE feels that the Corps of Engineers
permitting should not be an issue because most of the site has already been disturbed by
recent construction activities not related to the current project and the remaining areas that
potentially could be considered as wetlands are to remain undisturbed by this project.
Three NorthPark / 8800 N. Central Expwy. / Suite 300 / Dallas, Texas 75231 / (214) 739-4741
Mr. Skipwith
10/'8/96
Page 2
The following items correspond to your comments regarding concerns you think the Federal
Emergency Management Agency (FEMA) might have during their review for a CLOMR
request.
(1) The Floodplain Work Map (Appendix I) is the primary map of interest to the FEMA.
The Grading Plan (Appendix J) is provided only as additional information which is not
required for a CLOMR request and could be postponed until a final Letter of Map Revision
(LOMR) is requested following the completion of construction. It is noted on the Floodplain
Work Map that only existing contours are shown. This is routinely done, with reference to a
grading plan (if provided) or cross section plots for representation of proposed conditions.
The FEMA finds this approach acceptable and has never commented to the contrary during
their CLOMR reviews. However, we can add the cross section location to the Grading Plan
if it will assist you in your review for the City.
(2) The model used by NDMCE is believed to be the effective Flood Insurance Study (FIS)
model. This was verified by comparison to the most current Floodway Data Table and by
confirmation with the FEMA's Region VI Office that no LOMR's have been issued since the
effective date of the Floodway Data Table for the Elm Fork in tF, e project vicinity. Although
a CLOMR was issued for the Sandy Lake Road and Mclnnish Park Improvements, they
have not yet been constructed. The FEMA probably will not modify the effective FIS model
based on proposed modifications; they must have been physically constructed before they
will be incorporated into the effective FIS model. If the FEMA has a different effective FIS
model from what NDMCE used, then that issue can be addressed during the course of the
FEMA review.
Based on NDMCE conversations with Dallas County Public Works. construction of the
Sandy Lake Road bridge will start soon but will require 18 to 24 months to complete, which
means it will be at least this long before it could possibly be incorporated into the effective
FIS model. Current plans for the Sandy Lake Road Property reclamation are to construct
the modifications as soon as all regulatory agency approvals are obtained. In view of
agency review times and anticipated construction time. a LOMR for the completed project
should be obtained in 12 to I5 months. Therefore, the currently effective FIS model will
remain unchanged throughout the duration of this projecT.
(3) Only one cross section in the effective ~I~ model fransec~ts the project site. This ~ecfion
was modified to represent the pre-project and post-project conditions. Given the small
portion of the overall Elm Fork floodplain occupied by the project site, NDMCE felt this was
adequate representation. Further cross sections were added to the models for addressing
the CDC criteria, as illustrated in the accompanying report. As exhibited by both the
CLOMR and CDC Report results, the impact of the project site on the Elm Fork floodplain is
negligible.
Mr. Skipwith
10:"8~'96
Page
We hope these explanations and the accompanying CDC Report will serve to resolve these
issues. If you have any questions or would like to discuss these items further, please let us
know.
Sincerely,
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
Mark D. Walter, P.E.
enclosure
cc: Mr. Kenneth M. Griffin, P.E. - City of Coppell