HomeMy WebLinkAbout53 West District Maint Shop 00-1 103 Holleman DrI c
s MM.II c
August 20, 1999
Mr. Jim Holster
Holster & Associates Architects
7607 Eastmark Drive, Suite 200
College Station, TX 77845
REVIEWED FOR
cn~~PLIANCE
JAN 2 7 2000
COLLEGE STATION
ENGINEERING
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Re: Supplemental Drainage Evaluation for the Proposed West District Maintenance Building_
College Station, Texas
Dear Mr. Holster:
In accordance with your request, CSC Engineering & Environmental Consultants, Inc . (CSC) has
conducted a review of drainage issues associated with the development of the site of the proposed West
District Maintenance Building (the "Site"). The Site is located just east of the Wellborn Road and
Holleman Drive intersection in College Station, Texas.
Purpose and Scope of Drainage Review
Our review was conducted to evaluate the potential net increase of precipitation runoff resulting from the
proposed development of the Site by the construction of the West District Maintenance Building and
associated paving areas. Specifically, a drainage report was prepared for the Wayne Smith Little League
Park which includes the Site and proposed development. The development of the Site considered in that
report was limited to the construction of a 3,600 ft2 warehouse structure without ancillary paved areas .
However, final development plans for the West District Maintenance Building to be located on the Site
will entail the constrnction of a larger warehouse structure (5 ,000 ft 2) and the addition of approximatel y
I 0 ,292 ft 2 of support paving . This increase in "imp e rvious area" will result in a slight increase in runoff
flows fr o m the Site and is the subject of thi s lett e r .
Sources of Information Used in the Drainage Revi e w
Our rev ie w of drainage c o nditi o ns at th e Sit e was base d. in pa rt . on in fo rm a ti o n p rov id ed by Holster &
Assoc ia tes Archit ec ts regardin g th e prop osed stru c ture and s upport pav in g. a nd in fo rmati o n prese nt ed in
th e drain age rep o rt fo r th e W ayne Smith Littl e Lea g ue Park . That drain age re po rt wa s pre pared by Mr.
Rick Ro b e rtson , P .E . and is e ntitl ed "Dra inage Re port , Propos ed Wayn e Smith Little Leagu e Park ,
Coll ege Station, T e xas , Ma y 1997 ." A bri e f description of our evaluati o n of th e pro vid ed information and
our conclu s ions reg arding pot e ntial drainage iss ues are prese nt ed in th e foll o wing sec ti o ns of this lett er.
Description of Project
The propos e d proj e ct will include th e construction of a 5 ,000 ft 2 maintenance building and support
paving . The refer e nc ed report subdivided th e area of ir.t e re st into six distinct drainage basins based on
topographic features and drainage structures at th e sit e. The drainage basin in which the Sit e was located
was designated as basin 4 and consists of an area of approximately 2.37 acres. Runoff flows exit the Site
in a northerly direction onto an access road from Holleman Drive and th e n flow in a southerly direction
within the curb and gutter channel of the access road to a curb opening on the eastern side of the street
3407 Tabo r Road
Brya n . Texas 77808
Phone (4 09) 77 8-281 0
Fa x (409) 778-0 820
..
,,,. .. c Is I c
Mr. Jim Holster
Page 2
August 20, 1999
where the flows are routed to a flume and drainage channel. The original proposed project resulted in
calculated predevelopment and post development flows of8 .2 and 17.1 cfs , respectively . In addition, two
profile models were pre pared by Mr. Robertson for the existing channel configuration and analyzed for
discharges from the 10 , 25, 50, and 100-year storm events . The analysis indicated that th e proposed site
development would not increase flood elevations upstream or downstream of the proj ect site .
Supplemental Evaluation and Analysis
The actual anticipated flow from drainage basin 4 based upon the presentl y planned development of the
Site was computed consistent with the assumptions and procedures used in the referenced drainage report .
The new computations indicate that the post development flow rate from drainage basin 4 will be 18.4
cfs, compared to 17 . l cfs as presented in the original drainage report . This increase in anticipated flow
from the project site is due to the increased "impervious" area of 11,692 ft 2 (structure and support paving)
compared to the assumptions made in the original drainage report . This increased differential flow rate of
1.3 cfs represents a very nominal increase in runoff compared to the combined contributory area of the
project site. In fact, the total flows in the previously referenced drainage channel for the 25-year event
were formerly calculated to be approximately 139 cfs . The additional flow of 1.3 cfs is less than 1 percent
of the total channel flows.
As previousl y discussed, the increased flows from the Site in basin 4 will be directed to th e access road
and will flow via the curb and gutter channel to Inlet 5 which is an op e ning in the curb at the top of a
flume . Accordingl y, an analysis of Inlet 5 was performed to evaluate capacity issues re lated to the
increased flow rate . The anal ys is was consistent with the procedures used in the original drainage report
and indicates that the flow depth in the gutter increased from 0.41 ft to 0.43 ft for the 25-year storm . The
capacity of the designed curb inlet to handle th e additional incremental flow also appears to be adequate
for the proposed development.
Conclusion
Ba sed on the aforemen ti oned ana lys is and th e proposed de ve lopment as ou tlin ed abo ve . th e calculated
incr e me ntal in crease of 1.3 cfs for th e stormwatcr runoff from the Sit e can be accommodated by Inl e t 5
and \\ill not res ult in a sig nifi cant drainag e impact do m1 stream o f th e projec t site .
Pl ease contact either of th e und e rsign ed indi v idu a ls at (40 9) 778-281 0 if you ha \e a ny qu est ions or need
additi o nal informatio n concerning this matt er.
Respectfu ll y.
W .R . Cullen , P .E .
Senior Engineer
WRC:mf