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August 28, 2014
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Board of Directors
Denton County Levee Improvement District No. 1
C/O Julianne Kugle
1980 Post Oak Blvd., Suite 1380
Houston, Texas 77056
Re: Review of Floodplain Study Submittal by Teague Nall & Perkins — Conditional Letter
of Map Revision (CLOMR) for Denton Creek Pedestrian Bridge
Dear Board of Directors,
We have completed a technical review of the Conditional Letter of Map Revision (CLOMR) for
Denton Creek Pedestrian Bridge prepared by Teague Nall & Perkins, dated April 30, 2014,
revised on August 13, 2014, and received on August 14, 2014. This general review consists of
checking the submittal package for potential impacts to the levee and channel improvement
section of Denton Creels operated and maintained by the Denton County Levee Improvement
District No. 1 (DCLID-1), and checking the submittal package for completeness and compliance
with the City of Coppell floodplain ordinances, regulations, and policies.
The following comments are a result of this review:
DCLID-1
1. The proposed bridge crossing causes an increase in water surface elevations on Denton
Creels for the 500 -year fully developed watershed condition by 0.05 feet. This increase is
considered insignificant compared to the water surface elevation increases that will be
caused when the fully developed discharge (55,500 cfs) determined by the U.S. Army
Corps of Engineers (USACE) becomes the effective discharge for Denton Creels for
Federal Emergency Management Agency (FEMA) mapping purposes. Adoption of this
discharge for the 500 -year flood event may be up to 40 plus years away. Under existing
FEMA discharge conditions, the proposed trail bridge crossing will not decrease the 500 -
year plus 3 feet of freeboard protection required for the leveed section of the District.
Therefore, the proposed trail crossing has no significant impact hydraulically on the
DCLID-1.
2. An easement from DCLID-1 for the proposed trail crossing will be required.
3. A final set of drawings for the trail crossing should be provided to DCLID-1 prior to
construction. A construction schedule should also be provided.
HALFF ASSOCIATES, INC.
1201 NORTH BOWSER ROAD TEL (214) 346-6200 WWW.HALFF.COM
RICHARDSON, TX 75081-2275 FAX (214) 739-0095
No HALFF
4. All damage to District property caused by the contractor shall be promptly repaired and
restored at contractor's expense (this includes grassing).
All track equipment and vehicle(s) weighing in excess of a gross of 20,000 pounds
proposed to be used on the levee requires advanced written approval from the District.
6. No equipment or vehicles shall use the levee after a rainfall event (defined as more than
one (1) inch of rain in a 12 hour period) until cleared for use by the District.
7. The District and its representatives shall have the right to inspect all work which pertains
to District facilities (channel and levee) at all reasonable times and shall have full and
complete access to all inspection and testing reports.
City of Coppell Criteria and FEMA
1. Please verify the `n' values used in the right overbank just upstream and downstream of
the proposed trail bridge crossing. The response letter dated August 13, 2014, states that
the city will maintain a 50' clearing around the bridge for safety and visibility.
2. Please verify the bridge topwidth in all models; the fully developed model shows 12 ft.,
the FEMA conditions model shows 14 ft., and the plans show 12 ft. 3 in. Revise and
resubmit accordingly.
Be advised that the bridge geometry in the FEMA models does not match that shown in
Exhibit 2.1. Please revise and resubmit.
4. Topwidths determined by the proposed conditions FEMA model do not compare to those
shown on the workmap at cross-sections 24585, 24700 and 25530. Please revise the
workmap and/or the model to be consistent as far as topwidths are concerned.
5. Floodway topwidths determined by the proposed conditions FEMA model do not
compare to those shown on the workmap at cross-sections 23800 and 24700. Please
revise the workmap and/or the model to be consistent as far as topwidths are concerned.
6. Please verify the location of the right bank station at cross-sections 24585, 24620, 24660,
and 24700 of the proposed conditions FEMA models. The cross-sectional geometry of
these cross-sections do not differ much from the cross-sectional geometry shown in the
fully developed model, however the location of the right bank stations differ between the
models. The response letter dated August 13, 2014, states that this item was "Revised",
however, our review shows differently. Please revise and resubmit.
This review was performed for the benefit of the Denton County Levee Improvement District
No. 1 and the City of Coppell. This is not a detailed engineering review of any construction
,;; HALFF
plans, and Halff Associates, Inc. assumes no liability for the adequacy of the planning, design or
construction of the project.
Do not hesitate to call me at 214-346-6245 if you have further questions or comments
concerning this review. Please include the reference "AVO 28540" on all correspondence.
Sincerely,
HALFF ASSOCIATES, INC.
Russell P. Erskine, P.E., CFM
Project Manager
Attachments (1)
cc: Kyle J. Dykes, P.E.
Teague Nall & Perkins
Mike Garza, P.E.
City of Coppell
John Elias
City of Coppell