PA1301-CS141216
www.tnpinc.com
December 16, 2014
engineers
surveyors
landscape architects
Mr. Russell Erskine, P.E., CFM
Halff Associates
1201 North Bowser Road
Richardson, TX 75081-2275
RE: Response to City of Coppell comments
Conditional Letter of Map Revision (CLOMR) for Denton Creek Pedestrian Bridge
TNP# CPL14036
Dear Mr. Erskine,
This letter serves as a response to City of Coppell review comments provided by Halff Associates on
November 14, submittal of the above-referenced CLOMR. As you are
aware, the CLOMR is being prepared on behalf of the City of Coppell Parks Department.
In addition to the responses below, please also find attached revised digital models and a revised
workmap. Upon your approval of the submitted data, TNP will provide finalized copies of the entire
CLOMR packet to the City and DCLID.
Response to City of Coppell Comments:
1.Be advised that the bridge geometry in the FEMA models does not match that shown
in Exhibit 2.1. The low chord of the bridge in the model is approximately 1 foot lower
at the center of the bridge than that shown in the exhibit. Please revise and resubmit.
The model has been revised to match the low chord elevation seen in
Exhibit 2.1.
2.Topwidths determined by the proposed conditions FEMA model do not compare to
those shown on the workmap at cross-sections 24585 and 25530. Please revise the
workmap and/or the model to be consistent as far as topwidths are concerned.
The Regarding cross-section 24585, we have confirmed that the top width
shown in Standard Table 1 of HEC-RAS does not match the total top-width
measured in the HEC-RAS cross-sectional view. This is a result of the high
ground located between Denton Creek and the Andy Brown Park east lake.
This appears to be a nuance of HEC-RAS reporting. We have found the
measured top-width on the workmap to be in close accord with the top
width measured in cross-sectional view of HEC-RAS.
Regarding cross-section 24585, the models and workmap have been revised
such that all topwidths match.
Fort Worth 1100 Macon StreetFort Worth, Texas 76102817.336.5773 Dallas 17304 Preston Road, Suite 1340Dallas, Texas 75252214.461.9867
Denton 1517 Centre Place Drive, Suite 320Denton, Texas 76205940.383.4177 Sherman 200 North Travis Street, Suite 500Sherman, Texas
75090903.870.1089
Registered by the Texas Board of Professional Engineers, Firm No. F-230 Registered by the Texas Board of Professional Surveyors, Firm No. 100116-00
3.Be advised that the bank stations in the revised existing and proposed conditions
floodway models do not match that of the revised existing and proposed conditions
multi-profile models. Please revise the models so that they are consistent with each
other and resubmit.
The bank stations have been revised in the multi-profile and floodway
models.
4.The right overbank floodway encroachment at cross-section 23800 falls within the
channel based on the bank station locations. Please revise the floodway model so that
the floodway encroachment falls outside the bank station at this location.
The bank station has been revised as recommended.
5.The un-encroached 100-year water surface elevations in the floodway model should
match the 100-year water surface elevations of the multi-profile model. Please revise
and resubmit.
After adjusting the bank stations, the un-encroached 100-year water surface
elevations in the floodway model match the 100-year water surface
elevations in the multi-profile model.
Please feel free to contact me should you have any questions.
Sincerely,
tnp
teague nall & perkins
Niraj Acharya, P.E., CFM