FS9903-CS 990330 8174610322
MAR--~O--99 TUE 84:25 P~dak!ORRISON HYDROI_OGY ~4618~22 P. 81
Morrison Hydrology Engineering, Inc.
EMNL: ronmcr'7777C~l.com
Fax Transmittal
Date: Ivbreh 30, 1999
Number of Pages Sent Including This Cover Sheet; 5
'to:
Mr, Kenneth M, Gri~n, P.E,
Assistant City Marroger
City Engineer
City of Coppeli
255 Parkway Blvd.
P.O. Box 478
Coppell, .texas 75019
Off 2 14-304-3679
Metre 214-471-2251
Fax 214-304 3673
Subjet't:
Review of CLOME-F and CDC subnxittal for a 10 acre and 48 acre tract south of Sandy Lake Road and
West of McARhur Blvd.
Comments:
We just received a fax copy of the attached review by Kinfley Horn and Associates. Please note that Lhc
review recommendations include the statement, "This study is approved fez submittal to FEMA...'. We
would like this subinitial to occur as seen as possible. Please let me know if we can help in this process in
any way.
Relating to the other comments, we will provid~ a nSpoDse tomenow evenin$. We believe that these
comments relate to issu~ that would not affect FEMA approval of the project. Mo~t of the comments
require explanations of the repofi and relate to future site development plans. We will be most happy to
provide these quickly,
Thank you in advance for yottr quick response to this important proju,'t.
8i74610322
/ 9 11 5~ FAX 9~3938~0 D~LA8
' 03/30 9
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4616
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Kimley-Hem
and Assooiatas, Inc.
March 28, 1999
I
SU~e 1800
12100 Pafg CennJ Drive
Oilas, Tens
75951
VIA FACSIMILE'
el -Tz\ Baq- 55'-70
Ken Griffin, P.E.
Director ofl~ngineering and Public Works
City of Coppell
P.O. Box 478
Coppell, TX 75019-440~
iF 79 -
L
F,e, r'c,r-
Review of a CLOM'R -F and CDC submittal for a 10 and 48 Acre
Tract south of Sandy Lake Road and west of MeArthur BIrd.
Dear Mr. Griffin:
We have completed Cur initial review of the FloodStudy for a C£OMR.F on a
I0 and a 48 acre tract in Co]~pell, Texas South o/Sandy/,a/ca Road and Wast of
MMrthur Blvd. pr~p~ed by Morrison Hydrology Engineering Inc. dated
September 2 l, 1999 (nOte this signature date appears incorrect as this iS only
March). Our review comments, which 0r0 summarized below, are divided into
two categories; CLOMR-F and CDC.
The following are comments regarding the CLOMR-F submittal:
General
I. A site pla~ or exhibit was not been included in the CLOMR-F submirtal whh
proposed topography. and therefore cross-section information in the model
was not verified. When plans axe snbmitted to the City, they should be
checked to match the topography and conditions as indicated in the study.
2. In general, the exhibits are missing legends for hatch marks, the font scare is
unreadable (tom names, contour labels). and information is hard to find.
Exhibits do not need to be resubmitted for this CLOMR-F subminal to the
City, but for the FEMA submittal and the future LOMR-F Submittal tO the
City, pleas~ revise these workmaps. This includes using a larger overall
scale for the e.~hibits, larger font scales, identifying roads and site f'eaturcs
more Clearly, and providing a legend per line or hatch marks. Please include
the location of all exhibits, maps, and tables in the table of contentS, The
existing and proposed floodplan should be clearly identified.
Coat,
II
TEL 97'Z 770 1300
FAX rr4 239 M20
8174610322
MAR--~--~9 TU~ ~4~6 Ph~ORRISON HYDROLOGY ~4610~22 Pfo~
03/~0/89 ~ 11:56 F~ 9722393&~0 D.t~$ ~002
KImley-Horn
and Associales, Inc.
Ken Griffin, ]vf~rch 2 S. I ~, Iss 2 or2
City Requirements
3. Do tthe hatched areas on the "FLOODPLAIN FILL PP, OJECT PROPOSED
FLOODPLAIN FLOODPLAIN" exhibit represent the resulting floodplain
after gading o~' the areas that will be graded?
4. Page 3 of the report states" A chcck ~'as made to ensure that this elevation is
higher than the design flood plus one foot and higher than the current Corps
of Engineers study in this area." The reviewer is assuming the term "this
elevation" is referring to the FEMA FIS elevation plus two feet, Or in other
words, the finished floor (FF) elevation. lfthe FF elevations were computed,
v/here iS this information? The reviewer is assuming this is based on Table 1
elevations, plus the required one or two feet of freeboard. Please provide this
information, reference table I in the report text. and state the conclusions of
this comparison.
5. Please clarify in Table I that the stormwater management information is
based on ultimate flows and the FI~MA FIS ia based on existing flows. The
FEMA FIg hydroloiy is based on parameters for what year(i.e. I996, 1970s,
etc)? What is the hydrology of the COE model based on (existing or
ultimate)?
6_ Was the Nathan D, Maier CLO1ViK then submitted as a LOMR to FEMA. In
other words, wM this project actuaily constructed or modified as specified in
the CLOM_P, submittal to FEMA. Please clarify with a note by Table I that
the FEMA FIS study referenced is the Nathan D. Maicr study,
7, There appears to be a 75-ft to100-ft wlde chmmel alonl Sandy Lake P, oad
on the property. Information must be provided during the site planning
process to ensure that
· the fill does not interrupt historical flow from upland areas into Denton
Creek
· there is adequate capacity in the channel to convey site and upland runoff
without impacting the site
· flood elevations are determined for the creek and finished floor
elevations meet City criteria for this area
8. This channel must remain part of the mapped F3EY-,A floodplain. It is unclear
based on exhibits and discusSiOn in the report whether this is the case.
Currently, the floOdplain for this channel is mapped up to MacArthur
Boulevard.
9. Agree with statement that there iS no conveyance in the southwest area of the
site; however, please confirm once the site is regraded that the proposed pond
area will function similarly to current conditions. Will the fill restrict
floodwater from reaching the pond? How does the water flow into this area?
10. Methodology for hydrology has not been provided. Please explain how the
discharge for the 48-acre tract was determined to be 5000 cubic feet per
second (cfs) for the 100-year event and standard project flood. Please
explain how the discharge for the 10-acre tract was determined to be I000 cfs
for the 100-year event and standard project flood.
1 I. The report text specifies that the City-Wide Storm Water Management Study
was used tO determine design flood elevations. The Nathan D. Maier study
from/uly 1996 was used as the ~SMA) existinS (;Ondltions for the site.
Please explain how the ~vater surface elevations were determined in the
and Ass0ciales,
storage pond computations. It appears for the 4S-acre tract that the water-
surl~ce elevation begins at the 100-year or 500-year water-surface elevation
of the StOrmwater management study section 936;20 (cross-section 1) and
ends at se,~tion 92300 (cross-seet~on 8). Please confirm. Also, please show
on the exhibit how cross-sections 93620 end 92300 relate to cross-sections ]
and 8.
12. Please explain how the water-surface elevation was determined for cross-
sections 2 through 7 oFthe 48-acre tract modeling run.
13. For the 10-acre tract modeling runs how were the 100-yeai~ and SPF ~vater-
surface elevations determined for crosS-sectionS 1 through 47 This
informallen needs to be explained in the text oFthe report and calculations
provided.
14. For the exhibits corresponding to the cross-sections for the 48-acre and 10-
acre tract
· please include north arrows on both exhibits
· for the l O-acre tract exhibit, the scale is readable, however it is difficult
to understand how this blown up area relates to the entire site and cross-
sections along Denton Creek. Please Frovide more area on the exhibit
(24"x36" instead of 8 l/2"x ] ] ")
· for the 48*acre tract exhibit, please use a larger scale For the map and a
larger font seals| the area of the site shown is adequate
15. Please include the storage table located in Appendix 7 in the body of repor~
as Table 2. PZease state specific information and conclusions regarding this
table and ana[ysis ~ the body of the report.
F~M .4 R~quiremente.
16. This submittal appears to meet the intent oEthe requirements for a
Conditional Letter of Map P, evision based on fill.
17. Before the study is submitted to FEMA, please complete and use the latest
FSMA forms, These crux be downloaded from: w~w.fema,eov
If the engineer does not have access to the Internal, these can be provided by
the City upon request.
The study is approved for submittal to FEMA based on the intent of the
CLOMR-F submittal. However, the study is not approved for meeting City
requirements, Additional infom~ation will need to be provided to the City to
ensure proper drainage standards are met. All comments above most be satisfied,
and any additional comments arising out of the site planning process (where
more detailed information on topography and specific site drainage is provided)
must be met.
The following comments pertain to the CDC application:
]- The City should be copied on the transmittel form for the CDC application to
USACE, FEMA. TNRCC, NCTCOG. and all other cities. counties, and
agencies tcqulred.
2. The CDC application cannot be apprOved until a site plan is submitted.
3. The above comments on storage must be resolved before approval.
8174610522
A s H
MAR--~--99 TUE ~4:28 P~ !0RRI 0
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and Assodales. Inc.
Very truly yours,
larMrLEY-I'IORN AND ASSOCIATES, INC,
Suzanne She"fret
Project Manager
G:~-iYDRO\projeaS%c~,ppcll~gri~In2.dOC
cc: Ron Morrison
MorrisOR Z4ydrology ~ngi~eermg
viafaosimile, 8171274.1338