Carter Ph 3 FS-CS110316 cur l Kimley -Horn
and Associates, Inc.
March 16, 2011 •
12700 Park Central Drive
Suite 1800
Dallas, Texas
75251 -1516
Mr. Kenneth M. Griffin, P.E.
Director of Engineering/Public Works
City of Coppell
255 Parkway
Coppell, TX 75019
Re: Carter Addition Phase III
Grapevine Creek
Conditional Letter of Map Revision
Dear Mr. Griffin:
Kimley -Horn and Associates, Inc. (KHA) is in receipt of the Conditional Letter of
Map Revision submittal for Carter Addition Phase III, prepared by Dowdey,
Anderson & Associates, Inc., dated January 2011. KHA has reviewed the
documents for adherence to the City of Coppell Floodplain Management Ordinance
and National Flood Insurance Program regulations. KHA offers the following
comments based on a review of the above referenced documents.
1. The fully developed flows used in the study do not match the City -Wide Storm
Water Management Study. Fully developed flows used in the hydraulic models
should be revised to be consistent with the City's study.
2. Cross section numbering in the converted HEC -RAS model is inconsistent with
the effective hydraulic model. KHA recommends the applicant revise the cross
section numbering to be consistent with the effective hydraulic model for
clarity.
3. There are water surface elevation inconsistencies between the effective HEC -2
hydraulic model and the converted effective HEC -RAS hydraulic model. The
inconsistencies should be fully documented and explained in the CLOMR
submittal in accordance with the attached FEMA memorandum, dated April 30,
2001.
4. Floodway modeling was not included in the submittal. Floodway modeling
should be included in future submittals.
5. The FEMA MT -1 forms should not be included in the submittal. These forms
are not applicable for CLOMR submittals.
•
TEL 972 770 1300
FAX 972 239 3820
' - Kimley -Horn Mr. Kenneth M. Griffin, P.E.
„ and Associates, Inc. Mar 16, 201 2
Page 2
6. Geometry for existing and proposed cross sections 60 and 61 should be revised
based on the topographic information provided on the workmaps. In addition,
the channel geometry at cross section 60 differs between effective and
existing/proposed conditions. The existing/proposed hydraulic models should
be revised to be consistent with the effective model, or the applicant should
provide topographic information to support the revision.
7. The 500 -year floodplain should be shown on the existing and proposed
workmaps.
8. A fully developed workmap should be included with the study showing the
limits of the fully developed floodplain. The minimum finished floor elevation
should be shown for each lot adjacent to the creek.
9. KHA recommends the proposed grading and retaining wall be shown on the
proposed workmap, or the cross sections be added to the proposed grading plan.
10. Floodplain top widths shown on the existing and proposed workmaps are
inconsistent with the top widths in the hydraulic model.
11. The applicant should add a cross section to the hydraulic model through the lot
at the southwest corner of Heritage Oak Court and Legacy Drive to assess the
impacts of the proposed retaining wall and fill at this location.
12. The applicant should provide evidence of compliance with the Endangered
Species Act (ESA) per the attached FEMA Procedure Memorandum 64, dated
August 18, 2010. FEMA will not review the CLOMR without an Incidental
Take Permit, Incidental Take Statement, "not likely to adversely affect"
determination from the National Marine Fisheries Service or U.S. Fish and
Wildlife Service, or an official letter from the Services that the project has "No
Effect" on listed species or critical habitat.
13. The FEMA submittal letter should be revised to list Kenneth Griffin as the
Floodplain Administrator.
14. The property owner notification letter should be revised to list the specific
location and amount of maximum widening and narrowing of the Special Flood
Hazard Area, as required on the attached sample letter which is included in the
MT -2 instructions.
15. References to Beck Branch should be removed from the CLOMR report.
16. FEMA MT -2 Form 1 should be revised to indicate fill (Section 5.b).
17. FEMA MT -2 Form 1 should be signed by the requester prior to submittal to
FEMA.
18. The downstream tie -in location is cross section 59, downstream of the proposed
improvements. FEMA MT -2 Form 2 should be revised accordingly.
c 0 , 1 Kimley -Horn Mr. Kenneth M. Griffin, P.E.
and Associates, Inc. March 1 6, 2011
Page 3
19. The report should be signed and sealed by a Professional Engineer licensed in
the state of Texas, and should also include the Firm's registration number.
20. The vertical datum of the on- ground topographic information should be listed on
the workmaps and FEMA MT -2 Form 2.
The applicant should revise the Conditional Letter of Map Revision submittal 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. KHA may offer additional comments as a result of a technical
review of the revised submittal.
Please don't hesitate to give me a call at 972 - 776 -1781 if you have any questions or
comments regarding this letter.
Sincerely,
KIMLEY -HORN AND ASSOCIATES, INC.
■
Brad W. Pickering, P.E., CFM
Project Manager
Attachments: Policy for Use of HEC -RAS in the NFIP (FEMA; April 30, 2001)
Procedure Memorandum 64 (FEMA; August 18, 2010)
Property Owner Notification Sample Letter (FEMA)
Cc: Mr. Casey Ross, P.E., CFM; Dowdey, Anderson & Associates, Inc. (via email)