DR9202-CS 911230 (2) ALBER'I- H. H:\I.FF ASS()(~IA'I'E5. INC.
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'":'""':'-':':" ' December 30, 1991
AVO 12033
City of Coppell
P.O. Box 478
Coppell, TX 75019
Ami: Richard Terry, Fire Chief - Emergency Plan Coordinator
Re: FEMA Relief Grants - Brooks Lane
Dear Mr. Terry:
As requested by tile City of Coppe!l Engiueering Depm'tment we are providing
information m: the City-Wide Storm Water Management Study and in particulm' the Brooks Lane
flood relief project curremly under design. Tke City-Wide Storm Water Management Study was
commissioned in March of 1990 and accepted by city council on January 29, 1991. This study
covered over 2000 acres of flood plain land within tile city as well as 179 indMdual drainage
complaints. :\pproxirnate!y 50 flooding and erosion control projects aotal!ing over S8,000,000
were recommended :u,,d an implementation plan was developed to aid in budgeting for these
projects. In addition, .:t planning inventory was prepared x¥1,.ich includes an evaluation of land
uses and environment in the city. An open space plan consisting of over 200 acres of greenbelt
acquisition and three miles of additional hike and bike trails was iucluded in the final City-Wide
Storm Water Management Plan.
One of the projects identified in the Management Plan was the Brooks Lane/l lvnterxvood
Subdivision Draim',ge hnprovements. The garage at 415 Brooks Lane wats flooded during tile
Spring 1989 a:~d 1990 flood even.'.s. Ana!vsis of the storm sewer system within ttfis subdivision
showed approxim:ue!y 5-year capaci:y x¥ith no existing emergency overflow path. The following
factors contributed to this lack of capacity:
· Increases in flood ware,' surface elevations on Stream G1 due to
urbanization, thereby, increasing tile starting hydraulic grade at the storm
sewer outfall;
· lnconsismnciel in t!:e drainage design for the subdivision (drainage area
map and grading plan); and
· h:let time (time of concentration) utilized in design of tile system was too
long for the size of the drainage areas.
ALBERT H. HALFF ASSOCIATES, INC.
ENGINEERS · SCIENTISTS * SURVEYORS
City of Coppell
December 30, !991
Page 2
A copy of the report write-up including recommendations is included with this letter as
Attachment "A".
The ultimate recommended plan for improving drainage within this subdivision consists
of the installation of additional inlets and a sto, tn sewer diversion to relieve the existing system.
All of these improvements are estimated to cost S225,000 and will be implemented in stages.
The City of Coppell has chosen to begin implementation of the Stage 1 drainage
improvemen, ts by installing two storm sewer inlets on Brooks Lane in the ama where the
residence at 415 Brooks Lane was flooded. This will help to provide a small measure of relief
to this property owner. While this construction project in ongoing, preliminary design and
easement acquisition will be accomplished for the Stage 1 diversion.
The Brooks Lane/Humerwood Subdivision Stage 1 - Inlets Only project has an estimated
construction cost of $l 1,000 (see Attachment B - Estimate of Probable Construction Cost). This
project is currently under design. The following is a summaD, of actual and estimated costs of
completion of this first phase of construction.
Stage 1 Inlets Only
Constructi6n Plans & Specs. - Engineering Cost $3,896 ~
Bidding & Contract Award - Estimated $1,000
Construction - Estimated $11,000
Geotechnical Sen'ices During Construction - Estimated S800
Total Project Cost $16,696
: Carrentiy under contract Mth Albert H. Halff Associates, Inc.
The preliminary design and easement acquisition for the Stage 1 - Diversion will cost $4,500 in
engineering fees.
As a part of the Flood Plain Management Plan included in the "City-Wide Storm Water
Management Study" the reach of Stream G1 containing the existing ouffall for the Hunterwood
Subdivision stom~ sewer system is designated for preservation. It is a scenic wooded area
providing habitat for numerous smaU animals and birds. As mentioned previously, the flood
water surface elevations on this stream are a major reason for the lack of capacity in this storm
sewer system. However, in keeping with the flood plain management plan for the stream,
downstream channelization to lower the hydraulic gradient at the outfall was not considered a
viable option. The diversion plan will avoid all but a very minor amount of disturbance to this
ALBERT H. HALFF ASSOCIATES. INC.
ENGINEERS · SCIENTISTS · SURVEYORS
City of Coppell
December 30, 1991
Page 3
environment~ly significant area. The proposed improvements will 'also help to relieve standing
water problems within the subdivision.
The City of Coppell is currently "last-tracking" the inlet design and construction to
provide additional protection for this residence prior to the Spring 1992 rains. The current
schedule is:
Completion of Construction Plans 1-03-92
Specifications 1-10-92
Construction Bids Received 2-03-92
City Council Presentation - Contract Award 2-11-92
Completion of Construction 3-15-92'
* Dependent upon Weather Conditions
Please let us know if there is any flexibility in this March 15th deadline since winter is
a tough time of the year for construction projects.
We hope this information is helpful. Please feel free to call if you need further
information and/or back-up for this project.
Yours vex), truly,
ALBERT H. HALFF ASSOCIATES, LNC.
C.lean Hansen, P.E.
cc: Kenneth Griffin, P.E., City Engineer
Shohre Daneshmand, P.E.