HFLP-CS091118❑ � � Kimley -Horn
and Associates, Inc
November 18, 2009
Mr. Kenneth M. Griffin, P.E.
Director of Engineering/Public Works
City of Coppell
255 Parkway
Coppell, TX 75019
Re: 1550 E. Belt Line Road
Elm Fork of the Trinity River
Conditional Letter of Map Revision
Corridor Development Certificate
Dear Mr. Griffin:
Kimley -Horn and Associates, Inc. (KHA) is in receipt of the Conditional Letter of
Map Revision and Corridor Development Certificate submittals, prepared by Cotter
Associates LLC, dated October 5, 2009, for a property located at 1550 E. Belt Line
Road in the City of Coppell, Texas. KHA has reviewed the documents for
adherence to the City of Coppell Floodplain Management Ordinance, National
Flood Insurance Program regulations, and the Fourth Edition of the CDC Manual.
KHA offers the following comments based on a review of the above referenced
documents.
Conditional Letter of Map Revision
1. A full -size copy of the workmap should be provided with the submittal.
2. The scale of the workmap should be adjusted to show the full extent of the cross
sections through the subject reach.
The workmap should list the vertical datum of the survey information, and it
should be consistent with the FEMA vertical datum. Also, the vertical datum
should be listed on MT -2 Form 2.
4. The grading shown on the workmap included in the CLOMR submittal is
inconsistent with the grading shown on the Grading and Drainage plans
provided by the applicant. The workmap should be updated to be consistent
with the Grading and Drainage plans.
■
12700 Park Central Drive
Suite 1800
Dallas, Texas
75251.1516
TEL 972 770 1300
FAX 972 239 3820
❑ � � Kimley -Horn
and Associates, Inc
Mr. Kenneth M. Griffin
November 18, 2009
Page 2
The 100 -year and 500 -year floodplain through the subject reach should be
mapped based on results of the hydraulic model and topographic information
shown on the workmap. Separate workmaps for revised existing and proposed
conditions should be provided if both floodplain delineations cannot be shown
on the same map.
6. The existing topographic information shown on the workmap is inconsistent
with the existing topographic information shown on the Grading and Drainage
plans provided by the applicant. The workmap should be updated to be
consistent with the Grading and Drainage plans.
7. Cross section 844 +36 is incorrectly labeled as cross section 844 +86 on the
workmap. The workmap should be updated to reflect the correct stationing.
8. Based on conversations with FEMA, interpolated cross sections should not be
used for the revised existing and proposed condition hydraulic models.
Geometry for cross sections through the subject reach should be updated based
on available topographic information. The use of aerial topographic information
in the absence of on -ground survey is acceptable.
9. The FEMA effective floodway is incorrectly depicted on the workmap in the
vicinity of Grapevine Creek. The floodway boundary on the workmap should
be updated to be consistent with the FEMA effective FIRM panel.
10. There are cross sections in the hydraulic model located downstream of Belt Line
Road that are not shown on the workmap and may be impacted by the proposed
improvements. Show all cross sections on the workmap and update the revised
existing and proposed condition hydraulic models as necessary.
11. Annotated FIRM panels plotted at the same scale as the Effective FIRM panels
should be included in the submittal.
12. A floodway run was not included with the submittal package. The applicant
should include a floodway run to show that there are no negative surcharges or
surcharges greater than one foot.
13. A 500 -year floodplain run should be included with the submittal package. The
500 -year floodplain boundary should be shown on the workmap.
14. Development is proposed to encroach on the regulatory floodway. A
comparison of the revised existing and proposed condition hydraulic models
indicate a maximum increase in water surface elevation of 0.03' as a result of
this project. Article 4, Section C.5.c. of the City of Coppell Floodplain
Management Ordinance states that a project "will not increase the base flood
water surface elevations of the FIS regulatory floodway in effect at the time of
application for a floodplain development permit ". The proposed improvements
should be revised such that there is no increase in water surface elevation when
comparing revised existing and proposed conditions.
❑ � � Kimley -Horn
and Associates, Inc
Mr. Kenneth M. Griffin
November 18, 2009
Page 3
15. The report included with the CLOMR submittal references a Conditional Letter
of Map Revision based on Fill (CLOMR -F) at several locations. The report
should be revised to correctly reflect the application being submitted.
16. The report lists the pad elevation to be 442. The Grading and Drainage plans
provided by the applicant shows a pad elevation of 443. The plans or report
should be revised so they are consistent with each other.
17. The report states that the project drainage area is less than 100 square miles.
The drainage area for the Elm Fork at the location of the project is greater than
100 square miles. The report should be revised to reflect the correct drainage
area for the Elm Fork. The drainage area can be obtained from the Flood
Insurance Study for Dallas County, dated August 23, 2001.
18. Detailed volume calculations to verify the valley storage information included
in the report should be provided.
19. The report states that the City allows an increase in water surface elevation of
up to one foot. Increases up to a foot are allowed when the regulatory floodway
is not impacted. In cases where the regulatory floodway is impacted, the City
does not allow any increase in water surface elevation. This section should be
removed from the report.
20. The results tables provided in the report do not reflect the hydraulic models
provided on the CD. The report tables and HEC -RAS output should be updated
to reflect the digital models provided.
21. The applicant should be aware that FEMA's CLOMR application fee is
currently $4,400, not $4,500 as listed on MT -2 Form 1.
22. The effective FIRM panels show the communities of Dallas, Irving, and
Carrollton are located within the revision area. The applicant should notify
these communities of the project and signed copies of MT -2 Form 1 should be
provided prior to City of Coppell approval.
23. All affected communities and FIRM panels should be listed on MT -2 Form 1.
24. MT -2 Form 1 should be revised to list the affected FEMA zone designations as
AE and X.
25. MT -2 Form 1 lists a bridge /culvert as an affected structure, but no new
structures are proposed or existing structures revised. This structure should not
be listed, or additional information regarding this structure should be provided.
26. MT -2 Form 3 should be included with the submittal.
rui n Kimley -Horn Mr. Kenneth M. Griffin
and Associates, Inc November 1 8, 2009
� Page 4
27. Ground geometry at cross section 87191 is the same in the revised existing and
proposed hydraulic models; however, proposed grading is shown on the
workmap at this location. The hydraulic models should be revised to reflect
accurate revised existing and proposed conditions.
28. There are several cross sections through the subject reach where revised existing
and proposed geometry matches the effective geometry, but the Manning's "n"
values have been revised. Explain this discrepancy or modify the revised
existing and proposed hydraulic models to be consistent with the effective
model where geometry is not revised.
29. The applicant should submit proof that the Dallas County Utility and
Reclamation District has approved the proposed grading and drainage
improvements prior to City of Coppell approval.
Corridor Development Certificate
30. The Post - Project Boundary Map should be revised to show the full extent of the
cross sections through the subject reach.
31. Topographic information should be added to the workmap outside of the extents
of the on- ground survey information through the subject reach. The cross
sections within the subject reach should be modified based on available
topographic information.
32. The interpolated cross sections should be revised so they are based on available
topographic information.
33. The 100 -year ultimate condition floodplain should be mapped on the workmap.
34. The FEMA effective floodway is incorrectly depicted on the workmap in the
vicinity of Grapevine Creek. The floodway boundary on the workmap should
be updated to be consistent with the FEMA effective FIRM panel.
35. The report indicates a loss of valley storage in the 100 -year ultimate condition
flood. The drainage area of the Elm Fork is greater than 100 square miles;
therefore, the City of Coppell does not allow a decrease in valley storage in the
100 -year event.
36. Section 2.1.1.2 of the CDC Manual states that a base discharge of 4,000 cubic
feet per second should be used to determine the ineffective storage area for the
valley storage calculations. The valley storage calculations should be revised
based on this guidance.
r � Kimley -Horn Mr. Kenneth M. Griffin
and Associates, Inc Novembe 18, 2009
+ Page 5
37. The CDC application indicates the project will result in a maximum increase in
water surface elevation of 0.03 feet. Article 4, Section C.5.a of the City of
Coppell Floodplain Management Ordinance states a project must demonstrate
that it "will not increase the water surface elevations of the design base flood
(fully urbanized watershed) ". The proposed improvements should be revised
such that it does not result in an increase in water surface elevation.
38. The information on the CDC application is inconsistent with the valley storage
table in the report and provided hydraulic models. The application should be
revised such that it is consistent with the information provided by the applicant.
39. The CDC application lists cross section 871 +91 as the upstream boundary of the
project. There are additional cross sections between 871 +91 and Belt Line Road
that will be impacted by this project. The hydraulic model should be updated to
reflect these impacts, and the CDC application should be revised to list the
actual limits of the project.
40. The SPF ground geometry in the hydraulic models is inconsistent with the 1 -100
year ground geometry. The models should be revised so they are consistent
with each other.
The applicant should revise the Conditional Letter of Map Revision and Corridor
Development Certificate submittals 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 these comments.
Sincerely,
KIMLEY -HORN AND ASSOCIATES, INC.
N
Brad W. Pickering, P.E., CFM
Project Manager
Cc: Mr. Glen A. Dixon, P.E., CFM; Cotter Associates LLC