Lakewood B-SY080904
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P.O. BOX 294527
LEWISVILLE, TEXAS 75029
LETTER OF TRANSMITTAL
PHONE 972-906-9985
F"AX 972-906-99B7
From: Steven R. Homeyer, P.E.
shomeyer@homeyer-engineering.com
Date: 9/4/08
Re: HolI ood Drive Draina e
Pro'ect Number: HEI-08-132
I To: I City of Coppell
AU": Ken Griffin, P.E.
WE ARE SENDING YOU C8:I Attached D Under separate cover the following items:
D Shop Drawings
D Copy of Letter
D Submittals
D Change Order
C8:I Plans
D Other
D Samples
COPIES DATE NO. DESCRIPTION
1 9/4/08 Hydrology Study for 224 & 228 Hollywood Drive
"1f'<; s~ CA()~":> c,..e....:, -. q ~.~
S ~ 0(,..(2 r\tl O\Of', 1.-- v.;Ti ~t ~ b~
THESE ARE TRANSMITTED as checked below:
D For approval D Approved as submitted D Resubmit _ copies for approval
C8:I For your use D Approved as noted D Submit _ copies for distribution
D As requested D Returned for corrections D Returned corrected prints
D For review and comment D Other
REMARKS:
If you have any questions, please feel free to call me at 972-906-9985.
COPY TO: FILE
SIGNED: Steven R. Home er P
,.-.-
Hydrology Study in Support
Of a Fence at 228 and 224 Hollywood Drive
Coppell, Texas
/'
By
Morrison Hydrology Engineering, Inc.
861 HCR 1313 Hillsboro, Texas 76645
Phone 254-580-9636
Email ronmorrison@hughes.net
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Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page -2
Table of Contents
Introduction
Data Research
Hydraulic Analysis
Summary
Appendix I FEMA Information
Appendix 2 Plotted Drawing of the 100 year floodplain on the property.
Disk provided with the following information.
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HECRAS models
Work-maps
Plotted Cross Sections
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Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page-3
INTRODUCTION
Two residences at 224 and 228 Hollywood Drive would like to construct fences along their east
property boundary. Normally, this would not be a problem except for the fact that the east
portion of the lots for these residences is within a defined Federal Emergency Management
Agency (FEMA) floodplain (see appendix 1). It is the responsibility of the City ofCoppell to
insure that any work in the floodplain in their jurisdiction must not increase 100 year flood
elevations.
The purpose of this study is to determine a location for these fences that would not increase the
100 year flood elevation as defined by FEMA.
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DATA RESEARCH
In order to complete this study it was necessary to obtain the following information.
1. Morrison Hydrology Engineering, Inc. (MHE) sent a request to the FEMA library in
Alexandria Virginia on July 14,2008 for the FEMA Effective model of the Elm Fork of
the Trinity River, which is the stream controlling flooding on the subject lots. FEMA
responded by providing a HECRAS model and work-maps. Unfortunately the work-maps
did not match the effective HECRAS models. After some discussion it was discovered
that FEMA could not find the correct work-maps. The information received from FEMA
is included on a disk accompanying this report.
2. MHE contacted Mr. Mike Danella, P.E. U.S. Army Corps of Engineers - Fort Worth
District and obtained the correct work-map for the Elm Fork of the Trinity River. This
information is included on a disk accompanying this report.
3. The City ofCoppell provided a two foot topographic map of the area. This topography
was added to the Corps work-map. This information is included on a disk accompanying
this report.
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Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page -4
4. Finally, a detailed topographic survey of the two lots in question was provided by the
client. This was added to the City of Coppell topographic map and the Corps work-map
to provide a map of the entire floodplain.
HYDRAULIC ANALYSIS
This study was completed using the HECRAS Computer Model. The HECRAS program is
intended for calculating water surface profiles for steady gradually varied flow in natural or man-
made channels. Both sub-critical and supercritical flow profiles can be calculated. The effects
of various obstructions such as bridges, culverts, weirs, and structures in the floodplain may be
considered in the computations. The computational procedure is based on the solution of the
one-dimensional energy equation with energy loss due to friction evaluated with Manning's
equation.
The analysis began by duplicating the FEMA effective model. Next two cross sections 98200
and 98282 were added to the FEMA effective model by duplicating the closest FEMA cross
section and adding local topography based on the topographic survey provided by the client.
This existing condition model was run and the results shown on the drawings in appendix 2. The
area in question is shown below;
UpperT.nitySludJ - 22 lIIy1_ PI",,: 1..1 A__y.......d lII27/20OI
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100Xl
11000 12lXXl
&dat(II)
131Dl
A portion of Cross Section 98200 is shown above without fences.
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"......
Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page-5
UPllllrHnltySludy-22.,,_
PI...: ...1 Road..'.....aed 8/2712001
.(17
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v.s 10) YR
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10lJXl 10!Dl 1100J 1100> 12011 12!DJ 1300J
SlaIat (II)
A portion of Cross Section 98282 is shown above without fences.
.".- The result of the analysis at this location is shown below:
River: Elm Fork Reach: ef3 Profile: 100 YR
Reach River Sta Profile Q Total W.S. Elev.
(efs) (ft)
ef3 99708 100 YR 42900.00 448.36
ef3 98884 100 YR 42900.00 448.26
ef3 98282 100 YR42900.00 447.85
813 98200 100 YR42900.00 447.66
ef3 97919 100 YR429oo.00 447.44
ef3 97178 100 YR 42900.00 447.07
It should be noted that the FEMA model through this area elected to use an ineffective flow
option. This means that while the 100 year floodplain extends onto the property it is a stagnant
flow and does not contribute to the actual flood elevations.
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Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page -6
Based on a conversation with the City Engineer our next step was to place an 8' fence at the
property boundary. All flow behind this fence was blocked out using ground profile data. The
resulting model was run and the results shown below:
I.41*TrNySl:ucIy~ 22M-,.199U PIlIn fl1llllfbodfrtlr;'rllWil<<twthfence PiZ1f1.fX:S
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Stltien (ft)
13lXXl
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l.Q:)Ir Trfty' a:Ultt ~ 72 M., 1998 PIIn: f. fIoc:ldMIy' reriMd WIIh 'JInce tnlQ/D
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w; 100 YR
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100Jl 1100) l200J 13lXXl
Slaten (ft)
River: Elm Fork Reach: ef3 Profile: 100 YR
Reach River sta. Profile Q Total W.S. Elev.
(ets) (ft)
ef3 99708 100 YR 42900.00 448.36
ef3 98884 100 YR 42900.00 448.26
ef3 98282 100 YR 42900.00 447.85
ef3 98200 100 YR 42900.00 447.66
,,-. ef3 97919 100 YR 42900.00 447.44
ef3 97178 100 YR 42900.00 447.07
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Hydrology Study in Support of a Fence at
228 and 224 Hollywood Drive Coppell, Texas
Page -7
SUMMARY
A comparison between the model with and without fences shows that an 8' fence placed at the
east property boundary (or any other location on the property) would not result in an increase in
100 year flood elevations. This is as would be expected for two reasons.
1. The 100 year floodplain for the Elm Fork of the Trinity River is 1.8 miles wide, and our
area is only affecting 50 to 70 feet.
2. FEMA has modeled an area which contains lots 224 and 228 Hollywood Drive as
ineffective flow. This means the floodplain is stagnant in this area and does not
contribute to flow, thus it has no impact on flood elevations.
MHE has provided drawings and computer model on an attached disk. Please note that although
a fence would not affect the 100 year flood elevations at this location, there are still floodwaters
on the property during the 100 year flood. MHE has made no effort to predict the impact on
fences during a 100 year flood. Any fences completed in this area should be verified as viable
during a flood of this magnitude.
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PLOTIED DRAMNG OF T$E
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100- YEAR FJ.t,OODPLAIN~
ON THE PIlOPEIlTY
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