Connell Skaggs-CS 870402POWELL&POWELL
Engineers and Consultants
RECEIVED APl)
W. J. Powell P.E. -- 1925-1967
W. Llewellyn Powell P.E.
Richard L. Powell P.E.
J. Michael Milllcan P.E.
Michael D. McKenzle
April 2, 1987
P&P No. 3354-87-1-2
Connell Skaggs Addition
Lots 1, 2 & 3
Ms. Shohre Daneshmand
City of Coppell
255 Parkway Blvd.
Coppell, TX.
Dear Ms. Daneshmand:
This letter is in response to your concerns expressed at the DRC Meeting on March 24
regarding Powell & Powell's proposed "sheet flow" drainage across the refer,need site.
In reply we respectfully offer the following comm ,fits for your consideration:
1. During a 100 year storm event, the depth of flow at the center of the drainage I~ath'
(q=70 CFSe) will be approximately 0.7 feet deep with a velocity of 4.4 feet per
se,end. In contrast, based on the city subdivision ordinance, the City of Coppell
would allow a maJor arterial street to be designed at a 5% grsde to convey 60 'CFS
with a depth of flow at the gutter of 0.5 feet and a veloeity of 10.9 feet per
second. It is our opinion that the proposed drainage condition on our site is much
safer than the condition which would be allowed on the arterial street.
2. The contributing drainage area of the site runoff is relatively small (14 acres), and
therefore the design storm event will begin and pass quickly (20 minutes±).
3. We feel that our design, which will allow the site runoff to be conveyed in a wide,
slow moving manner, will cause much less erosion in the existing swale along the
west property line than if the on-site runoff were to be collected into a storm sewer
system and discharged at a concentrated point in the unprotected swale.
4. Upon the development of Lot 3 and the construction of a box culvert, extending
south to north near the west property line of the site, the sheet flow will be
collected in a series of combination curb-grate inlets which in turn will discharge
directly into the top of the future box.
Enclosed for your review are the following items:
A nomograph for flow in triangular gutters (City of Fort Worth Drainage Manual)
indicating the flow rate, depth and velocity of flow for a major arterial street on a
5% slope with one lane remaining open.
2. Calculations for the depth and velocity of flow in the front and rear of the site for
the 100, 50, 25, and 10-year storm events.
3. Sections at the center of the proposed drainage path showing the relationship of
existing, proposed and future grades in the area of the existing south/north swale.
3354b/0320
3988 North Central Expressway, Suite 1130 / Dallas, Texas 75204 / (214) 5224660
We trust that this information adequately responds
overland drainage across the site. If you have any
information, please contact James Koch of this office.
to your concerns regarding the
questions, or need any further
Very sincerely,
JMM:ck
enclosure
POWELL & POWELL
J. Michael Millican
Mr. Kevin White - Connell Development Co.
Mr. Bill Stapp - Connell Development Co.
Mr. Richard Watson - American Stores Properties, Inc.
Ms. Ann Gunning -Powell & Powell
3354b/0320
POWELL & ,Pp'"~LL
ENGINEERS & COI~.,aLTANTS
3988 N, Central Expwy. Suite 1130
DALLAS, TEXAS 75204
(214) 522-4660
SHEET NO. ~
CALCULATED BY ~
CHECKED BY
OF
DATE
SCALE
RECEIVED APR 0 2,1987
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POWELL & P.~,..LL
ENGINEERS & COho0LTANTS
3988 N. Central Expwy. Suite 1130
DALLAS, TEXAS 75204
(214) 522-4660
SHEET NO,
CALCULATED BY
CHECKED BY
SCALE
OF
DATE
DATE
..... o. 5 ~. t~
0/1
r3
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9000
8OO0
7000
&ODD
5000
4OO0
3000_
20OO
~000
9O0
8OO
70o j
600 _~
500 ~>
400
300
200
I00
'90
~- 80
~ 70
'-40
20
I0
RECEIVED APR 0 2 1987
I1 IS ROUGHNESS COEFFICIENT IN MANNING
FORMUL& ~PROP~IATE TOMATERIAL IN
BOTTOM OF CHANNEL
~ IS RECIPROCAL OF CROSS SLO~'E
N[.E,E.c[ mR m ,,OCEED,NGS ,,AG ,,GE ,so.
.01l ~/8,1~00
y.o. zz v
20
INSTRUCTIONS
~CT Z/n ~&TtO wrrH SLOP[ (S~
· NO CONNECT DISCHARGE(~.) WITH
DEP*~ H(ye~ THESE TWO LINES MUST
INTERSECT AT PIVOT LINE FOR
COMPLETE SOCUTION.
F0~ SH&LL0W V-
ID
7
z
S ~
.S
S
~ .o?
05
C~ ol C)
Sa'~Ja~ O CHANNEL
AS SHOWN USE
NOMOGR APH WITH
T
TO DETERMINE
DISCHARGE qelN
yoFOe TOTAL mS- -'-~------X-----J '
CHARGE IN ENTIRE
SECTION O THEN USE HOMOGRAPH TO
DETERMINE QblN SECTION b FOR DEPTH
JO
.08
.O5
.OI 0
_,
- .008
- .oo7 co
: .oo6 uJ
.005 bJ
- r'~
.OO4
0
,003
,002
-.OOI ~'~
TO DETERMINE DIS- ~ y'
CHARGE IN COMPOSITE
SECTION FOLLOW ~- ~i
INSTRUCTION 3.
TO O~TAIN DISCHARGE IN
SECTION O &T ASSUM[O ~ ~ ' - - '
DEPTH ~ OBTAIN OkFOR
SLO~ ~aTIO E k &ND DEPTH yl THEN ~,
(DEVELOPED BY U.S. BUREAU OF PUBLIC ROaOS
-2.0
-80
- .70
-- .60
- .40
'-.ao
.20
. .10
· .03
.02
.01
NOMOGRAPH FOR.FLOW IN TRIANGULAR GUTTERS
III-6
IFIGURE ]]]:-I