W Sandy Lk Addn-CS040625 2L4 3~,L 5573 ~.4K
06/25/04 FRI 05:39 FAX 214 361 5573 HALFF ASSOC INC ~001
III
· "... Halff Associates,, Inc.
ENGINEERS ARCHITECTS SCIENTISTS PLANNERS SURVEYORS
8616 No~hwest Plaza Drive
Dallas, Taxes 75225-4292
(214)346-6200
Fax(214) 361-5573
FAX TRANSMITTAL
TO:
Ken Griffin, P.E., City of Coppe[I
c: Richard Crow, Myers & Crow Company
DATE: June 25, 2004
AVO: 21905
FAX #:
FROM:
972-304-3570; 214-520-2015
B. David Littleton, P.E.
Email: dlittleton @ halff.com
PROJECT: Sandy Lake Road Site
Coppell, Texas
# OF PAGES 3 (including cover sheet)
[] URGENT
[] PLEASE REPLY
[] FOR REVIEW
COPY TO FOLLOW BY MAIL:
[] YES [] NO
ITEMS SENT:
Memo regarding storm water flow
Reduced D/A Map
COMMENTS:
Ken, here is the analysis for the section at the east property line.
SIGNED: B. David Littleton, P.E.
NOTE: The comments on and attachment to this cover sheet are inter.led only for the use of the individual or entity to which it is
addressed, and may contain information that is privileged, confidentiat, and exempt from disclosure under applicable law. If the reader
of this message is not the intended recipient, or the employee or Agent responsible for delivering the message to the intended recipient,
you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received
this communication in error, please notify us immediately by telephone and return the original to us, at the above address, via the U. S.
Postal Service. Thank you.
06/25/04 I:RI 05:40 FAX 214 361 5573 HALFF ASSOC INC [~]002
· ..'" Halff Associates, Inc.
ENGINEERS ARCHIT~:CT$ SCIENTISTS PLANNERS SURVEYORS
8616 Northwest Plaza Drive
Dallas, Texas 75225-4292
(214) 346-6200
Fax (214) 361-5573
TO: Mr. Ken Griffin, P.E.
City of Coppell
FROM:
SUBJECT:
B. David Littleton, P.E.
Emaih dlittleton @halff.com
Clint Philpott, E,I,T.
Emaih cphilpott @halff.com
Storm Water Flow
MEMORANDUM
DATE: June 25, 2004
AVO; 21905
PROJECT:
Sandy Lake Road Addition
A summary drainage analysis was prepared for the drainage area on and around the proposed West Sandy Lake
Road Addition. A significant area of off-site land drains through the subject property. The off-site area contains
approximately 51.6 acres of undeveloped land and approximately 9.0 acres of developed land. These areas drain
from an existing box culvert on the west side of the proposed Sandy Lake Road Addition by way of existing
channels. The total contributing drainage area from the subject tract is approximately 35.8 acres.
Flow calculations for both the existing basin conditions and for the subject property post-development conditions
were developed. The calculated flows can be found in the table on the Drainage Area Map provided. Once flows
were determined, a cross-section (A-A) of the east outlet channel was studied. This channel conveys all of the
flow from the property. An existing channel conveys the flow off the site at a s{ope of approximately 1.0%. A new
channel will be constructed to convey the storm water from the culvert and outlet along the south and east
property lines to connect back to the existing channel outlet. The new channel will have an approximate slope of
0.35%. The existing channel conveys approximately 246 cfs, and the proposed channel will convey
approximately 380 cfs {allowing for increased flow from the developed subject tract). This increase of flow and
decreased slope result in an increase in the flow depth of approximately 0.74 feet. Cross Section A-A on the
Drainage Area Map shows this increase. Also, the spread of water across the channel is increased approximately
34 feet and the velocity is decreased by approximately 1.2 fps. This decrease in velocity results in less erosive
conditions downstream.
This summary analysis does not include fully developed conditions upstream of ~he subject tract. Aisc, we have
not included potential drainage detention volumes in the new channel and in the truck court.
[] Attachments:
Copies: File
K:L?. 1000¢,21905\ad min\memoLM m 06-16-04.doc
06/25/04 FRI 05:40 FAX 214 361 5573 HAI,FF ASSOC INC ~003
llli Halff AssOciates, Inc.