Park West CC(1)-CS 900206PAAE 1 OF 2
DONALD E. DAVIS
CONSULTING ENGINEERS
5506 COCKRELL HILL ROAD
DALLAS, TEXAS 75236
(214) 337-2332
FEB. 6, 1~'~0
RO .... ELL D~YLE
CITY ENGINEER
CITY OF/COPPELL
DEPT. ~= PUBLIC WORKS
P.O. ~OX 478
732)F~EFOREST
COP~ELL, TEXAS 7501~
RE: PAR[( WEST COMMERCE CENTER - FINAL PLAT
C0190013. ARD
THIS IS A REQUEST FOR A MEETING WITH YOU AND YOUR STAFF CONCERNING THE STUDY
OF GRAPEVINE CREEK. THE F.E.M.A. LETTER OF AUGUST 18, 1987 OUTLINES THE LAST
SUBMITTALS AND INDICATES THAT A CONDITIONAL LETTER OF MAP REVISION WAS
APPROVED SUBdECT TO A NUMBER OF ITEMS BEING FURNISHED TO F.E.M.A..
WE ARE NOW WORKING IN COOPERATION WITH PAT ACKER, P.E. TO FURNISH THESE ITEMS.
AT THIS TIME PAT IS ADDRESSING THE PROBLEM OF THE HIGH VELOCITIES IN THE CREEl(
AND WILL FOLLOW THROUGH WITH ALL OF THE ITEMS REQUESTED BY F.E.M.A,. THIS
WORK MUST PROCEED ALONG WITH THE PLAT WORK AND CONSTRUCTION WORK BECAUSE
F.E.M.A. REQUIRES THAT THE STUDIES INCLUDE THE "AS-BUILT" DEVELOPMENT.
AS FAR AS PARK WEST COMMERCE CENTER IS CONCERNED - THE WORK PREVIOUSLY DONE TO
OBTAIN THE CONDITIONAL LETTER DEFINES THE FLOOD PLAIN AND WATER SURFACE
THROUGH THE PROdECT. THE HIGH VELOCITIES MENTIONED DO NOT OCCUR DURING THE
REACH THAT OCCURS WITHIN THE PROJECT. I UNDERSTAND THE NECESSITY OF CONTINUING
AND COMPLETING THE STUDY BUT I REQUEST THAT OUR PLAT WORK BE ALLOWED TO
CONTINIJE AS WAS DONE FOR THE PREVIOUS PLAT. ~ ~%f~l~ ~ ~,/~
THE SECOND SUBJECT TO BE DISCUSSED IN THE MEETING IS THE STORM WATER DESIGN
CRITERIA TO BE USED IN THE SUBDIVISION. THE RAINFALL INTENSITY CURVES IN THE
DOCUMENT CALLED FOR I~L~k~I~C~PELL SUBDIVISION ORDINANCE (TECH. PAPER 40) HAS
BEEN FOUND TO BE~CORRECT~ THE METHOD USED TO DERIVE THE FINAL RAINFALL
~~-~O~ED I~THAT WERE NOT CORRECT. LATER WORK RESULTED IN
~'~EVISIONS BEING PUBLISHED IN THE FORM OF "HYDRO~[5" gY~CONSERVATION
SERVICE. THIS REVISION HAS BEEN ADOF'TED BY THO"CITY OF DALL~ ALONG WITH
OTHER MUNICIPALITIES. THE RAI]~IF-~-{~, INTENSITY~MINUTE TIME OF
CONCENTRATION (100 YEAR RAIN) ~11.5 ~NCHES PER HOUR FRO~ T.P.40 WHEREAS TH~
INTENSITY FROM THE NEWER DATA ~S 6Sg//NCHES PER HOUR. i %~/, ~
i
FEB. 67 1990
CO190013. ARD
PAGE 2 OF 2
I HAVE WORKED ON A MAdOR PROdECT FOR THE CITY OF DALLAS RECENTLY AND THE 8.9
INCHES PER HOUR FIGURE WAS USED. ~-~-~q~T~
THE CITY OF COPPELL SUBDIVISION ORDINANCE ALLOWS A "~' VALUE FOR INDUSTRIAL
AREAS OF FROM 0.7 TO 0.9. IN ORDER TO COMPLY WITH T~4E ORDINANCE AND ALSO BE
REALISTIC ABOUT THE STORM WATER VOLUMES - I RECOMMEN/B THAT THE 11.5 INCHES PER
HOUR FIGURE BE USED BUT THAT A "C" OF 0.7 BE USED.' THE RESULT IS PRACTICALLY
THE SAME AS IF THE 8.9 INCHES PER HOUR WERE USED WITH A RUNOFF FACTOR OF
DONALD E. DAVIS
CONSULTING ENGINEERS
CC: DON GERKEN
LEE HANSEN
MIKE TUCKER
PAT ACKER