Cottonwood Est-CS150629
Via email
June 29, 2015
Mr. Michael Garza, P.E.
Assistant Director of Engineering
City of Coppell
265 Parkway Boulevard
Coppell, Texas 75019
RE: 157 Cottonwood Drive
Cottonwood Branch
Floodplain Study
Dear Mr. Garza:
Kimley-Horn and Associates, Inc. (Kimley-Horn) is in receipt of theFloodplain Study for 157
Cottonwood Driveprepared by DEH Consulting, LTD (DEH), dated June 19, 2015. Kimley-Horn has
reviewed the documents for adherence to the City of Coppell Floodplain Management Ordinance and
National Flood Insurance Program regulations. Kimley-Horn offers the following comments based on
a review of the above referenced study.
1. The report indicates several new cross sections are based on copies of effective cross
section 6710 or are interpolated cross sections. New or modified cross sections should be
based on the topographic information shown on the workmap.
2. Two accessory structures were previously constructed in the floodplain without permits.
These structures should also be included in the proposed hydraulic models to show they
cause no adverse impact to the floodplain. In addition, evidence should be provided that the
construction of these accessory structures meets the requirements of City of Coppell
Floodplain Management Ordinance, Article 5, Section A.
3. There are existing and proposed improvements located within the FEMA effective floodway
associated with Cottonwood Branch. This analysis also needs to be performed using FEMA
effective flows to show no-rise in floodplain elevation.
4. The proposed mitigation swale has upstream and downstream connections to the
Cottonwood Branch channel. What erosion protection is proposed in these areas to protect
against potential scour?
5. The HEC-RAS model shows the proposed mitigation swale has a 0.0% longitudinal slope.
The swale should be graded to maintain positive drainage. Kimley-Horn recommends a
minimum 1% longitudinal slope.
kimley-horn.com12750 Merit Drive, Suite 1000, Dallas, TX 75251972 770 1300
Page 2
6. A 30’ wide sanitary sewer easement is located in the rear of this lot. The existing easement
should be shown on the Floodplain Workmap to verify the proposed mitigation swale is
located outside of the easement.
7. Overbank reach lengths in the existing and proposed hydraulic models for cross section
7213 do not appear to be consistent with the cross section locations shown on the
Floodplain Workmap. The reach lengths should be verified and revised as necessary.
8. Discussion regarding USACE 404 permitting requirements should be added to the report. If
one is required, a 404 permit for the proposed mitigation swale must be obtained prior to
issuance of the Floodplain Development permit.
9. Evidence of compliance with the Endangered Species Act should be provided. The
applicant should refer to FEMA Procedure Memorandum 64 for additional information. An
official species list should be obtained from the U.S. Fish and Wildlife Service Information for
Planning and Conservation (IPaC) online system (https://ecos.fws.gov/ipac/).
The applicant should revise the study based on the above comments and resubmit to the City of
Coppell for further review. The applicant should include a written response to each comment as part
of the resubmittal package. Kimley-Horn may offer additional comments as a result of the review of
the revised submittal.
Please don’t hesitate to contact me at 972-776-1781 if you have any questions or comments
regarding this letter.
Sincerely,
Brad Pickering, P.E., CFM
Project Manager
Cc:Dale Hoelting, P.E. – DEH Consulting, LTD (via email)
kimley-horn.com12750 Merit Drive, Suite 1000, Dallas, TX 75251972 770 1300