Coppell Industrial-CS000322 Graham Associates, Inc.
CONSULTING ENGINEERS & PLANNERS
Centerpoint Two Suite 400/616 Six Flags Drive
Arlington, Texas 76011 - Metro 640-8535
March 22, 2000
Mr. Ken Griffin, P.E.
Ci:y of Coppell - Engineering
P.O. Box 478
Coppell, Texas 75019
-"~,Re: Coppell Industrial Addition - Bethel Road
Proposed by Ch,~pion. Partners
Dear Mr. Griffin,
Please consider this letter as our tectmical hydrologic calculations for the m-oposed
distribution facility on Bethel Road north of the USPS facility. Since the City's stated
criteria is to have the developed condition 100 year flood discharge no larger than the
existing condition (undeveloped) discharge, and the City does not have a specific
methodology for this sort of analysis in their drainage manual, we propose to use the
detention calculation procedure outlined in the City of Carrollton's Drainage Manual (see
att2ched). The Carrollton method has several advantages since it is compatible with the
rational equation and it provides a direct solution for determining the storm duration
which results in the maximum storage volume. The chief shortcomings are that it can not
'be used for large drainage areas (greater than 160 acres) or for multiple detention ponds~
in series, however these shortcomings are not applicable to this project. The Carrollton ') ~-~,~
method states; A..~i~-"-"'- '
- V = 60 x Qe / 2 x (Td - Tc) eq. 1
Where; V is the required storage in cubic feet
Qe is the allowable maximum discharge out of the detention
Pond; usually this is the existing condition discharge.
Td is the time to the peak outlet discharge, in minutes.
Tc is the time to the peak inlet discharge, in minutes.
When the Carrollton method is combined with a rainfall equation, instead of a rainfall
graph, Td can be determined from the follo~ving;
Qe = Qd = C x I x A where
C is the design runoff'coefficient, Cd, therefore
I = Qe / (Cd x A)
'I' is also the rainfall rate (P) in the rainfall equation. According to page 2-17 of the
TxDOT Hydraulic Manual, the 100 year rainfall equation in Dallas County is;
I = P = 106 / ((8.3 + Td)^.762 ) eq.2
The terms of this equation can be re-arranged to solve for Td as shown below;
(Td + 8.3)".762 = 106 / I
Td = (106 / I)^(1 / .762) - 8.3 eq.3
Combining equations 2 and 3 results in;
Td = ((106 x Cd x A / Qe)^1.3123) - 8.3 eq.4 lc~,"'
For our project, the existin~ condition discharge can be calculated from Qe = CIA where ~'~-~" ' '~"~
A is 98.1 acres (which is the site area excluding the Bethel Road dedication) and C is 0.3
(which represents an undeveloped condition as per the Dallas Drainage Design Manual ..........
[DDDM], page 1 of the appendix). 'l-'he variable I is dependent on the time of concen-
tration (Tc) for the existing condition which can be calculated from Tc = L / (60 x V),
where L is the length of the flow path, in feet and V is the flow velocity, in feet per '3 -' ~''~ .'"t -
second. In our case L = 2100 feet and V is 1 fps, (as per the DDDM page lb of the
appendix), therefore Tc =2100 / (60 x 1)=35 minutes. ~c: 4g ,,..:,., : ,
Using the TxDOT 100 year rainfall equation, this results in I = 106 / (8.3 + 35)^.762 or ~.j .-
I = 6.00 inches per hour. Therefore the existing discharge is;
Qe = 0.3 x 6.0 x 98.1 = 176.6 cfs
Substituting Qe = 176.6 and Cd = 0.9 into equation 4 results in;
Td = ((106 x 0.9 x 98.1 / 176.6)^1.3123) - 8.3
Td = 174.8 minutes ~'--* '5~,~,-7
Substituting Qe = 176.6, Td = 174.8 and Tc = 10 into equation 1 results in; ->'z' · .-3
V = 60 x 176.6 / 2 x (174.8 - 10) -. ¢
V = 873,110 cubic feet I :..:~'; a. ~.-~. ..
We propose to construct an on-site detention pond containing a storage volume of at least
875,000 cubic feet along the eastern edge of the property. The 'pond' will be normally
dpj' and outlet by gravity into a soon to be~m~roved ditch to the east. The pond's outlet
will be designed to pass a maximum o 7f~. 'cfs at a water level in the pond which
results in a storage of 875,000 cubic feet. Tike outlet ~structure, outlet ditch and pond
grading have not been designed at this time. \ t~>
Detailed design of the outlet structure, outlet ditch and pond grading has not been
initiated. Prior to starting detailed design, we would like your concurrence with our
proposed methodology for determining the alloxvable discharge and required storage
volume. This information will be very important to the consultant working on the
development immediately east of this project.
Please feel free to call myself or Chuck Stark with any questions you may have.
Sincerely,
Neal Chisholm P.E.
Graham Associates, Inc.
Cc; Jim Steward - Champion Partners
David Meinhardt - Meinhardt & Quintang
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~RROI~TON
. STORMWATER
AND
FLOOD PROTECTION
ORDINANCE
FEBRUARY 1994
NDM NATHAN D. MAIFR
CONSULTING ENGINEERS. INC.
D&llas, Texas
(214) 739-4741
FIGURE 24
Approximate Routing Method for Watersheds < 160 Acres
o STORAGE VOLUME' (V.)
n'- \ \C.x \ k,.x \ \,,.\ \..,~ ,
" Tcp TD TD + TCp
TIME (MINUTES')
V=(60) [ (QD[(TD -Tcp)+(TD+Tcp)]/2) - (QE[Tcp +TD]/2)]
in cubic feet.
or
V = 60 (QEt2) (TD - TCp)
Where: Qp = Peak discharge in cfs for developed watershed using storm duration equal to TCp.
QE = Peak discharge in cfs for watershed, full
existing
assuming
residential development and corresponding TC .
QD = Peak discharge in cfs for developed watershed, based on a storm
duration that yields the existing discharge for Cp and A.
TCp = Time o[ concentration in minutes for proposed development.
TD = Storm duration in minutes corresponding to ID-
ID = Rainfall intensity (inches/hour) for storm duration that
produces QD and is calculated using the following formula:
ID = :-:. ~)
(Cp A) Cf
Where:
Cp = Rational "C" for developed condition.
:
A = Drainage area in acres.
Cf = Frequency factor coefficient of 1.25 "
101
FIGURE 24, continued
Detention Basin Example:
Development Data:
Drainage Area = 160 acres
Residential C = 0.55
Residential TCR = 15 minutes
Developed Cp = 0.70
Developed TCp = 10 minutes
Cf = 1.25
For the 100-year storm:
IRES =IP 7.52 in/hour (from Figure 1)8.82 in/hour.
QE .= QD= (1.25) (0.55) (7.52) (160) = 827 cfs
Qp = (1.25) (0.70) (8.82) (160) = 1235 cfs
QD 827
ID = = = 5.91 in/hour
(Cp A) Cf (.7)(160)(1.25)
From Figure 1, for ID = 5.91 in/hour,
TD = 28 minutes
V = 60 ( 827 )' (28-10)
( 2 )
= 24,810 (18) = 446,580 cubic feet
102
CITY OlZ DALLAS
PUBLIC WORKS
btAY 1995
RUNOFF COEFFICIENTS'AND MAXIMUM INLET TIMES
Runoff Max. Inlet
' Coefficient Time
Zone Zoning District Name "C" In lttnuLes
A(A) Agriculture 0.30 20
R - lac(A) Residential 0.45 20
R - 1/2ac(A) Residential 0.45 20
R - 16(Al Residential 0.55 15
R - 13(Al Residential 0.55 15
R - 10(Al Residential 0.65 15
R - 7.5 (Al Residential 0.65 15
R -5(A) Residentia! 0.65 15
D(A) Duplex 0.70 10
TH - 1(Al Townhouse 0.80 10
TH - 2(Al Townhouse 0.80 10
TIt - 3(Al Townhouse 0.80 10
CH Clustered Housing 0.80 10
~ = I(A) 14ultifamil.y Residential 0.80 10
t~ 2(Al Multifamily Residential 0.80 10
~: - 3(Al :4ultifamily Residential 0.80 10
I~ ' 4(~) Multif~nJly Residential 0.80 10
Mt(A) Mobile Nome 0.55 15
NO(A) Neighborhood Office 0.80 10
LO - 1 Limited Office - 1 0.90 10
LO - 2 LtmiLed Office - 2 0.90 JO
LO - 3 Limited Office - 3 0.90 10
MO - 1 Midrange Office - 1 0.90 i0
MO - 2 Midrange Office - 2 0.90 10
GO(A) General Office 0.90 10
NS(A) Neighborhood Services 0.90 10
CR Community Retail 0.90 10
RR Regional Retail 0.90 10
CS Commercial Service 0.90 l0
LI Light Industrial 0.90 10
IR Industrial Research 0.90 10
II4 Industrial Manufacturing 0.90 lO
CA --I(A) Central Area - 1 0.95 10
CA - 2(Al Central Area - 2 0.95 lO
MU - 1. Mixed Use - 1 0.80 lO
MU - 2 Mixed Use - 2 0.80 l0
MU - 3 Mixed'Use - 3 0.90 10
HC ~' t.' Multiple Com~rcial - i 0.90 10
MC -.2 Multiple Comercial - 2 0.90 10
MC - 3 Multiple Con~nerc~al - 3 0.90 10
MC - 4 Multiple Co~nerc!al - 4 0.90 l0
P(A) Parking 0.95 10
NON-ZONED LAND USES
Runoff
.., Coefficient'
--- Land Use "C"
Church ......... 0.8
School 0.7
Park 0.4
Cemetery 0.4
.50 -
° /
.oz - d --
~ ~] .-. _..
.005 -
I. I I I I- I I I I I I
1 2 4 6 ]0 ., 20
Average velocity, ft/sec
Fijcurc 3'l.-A~cn~r s'th)cllles [or clttrnnlj,~;c Irnvc! lim~. rot .qhnlJow cnncenlrz~led flow.
(210-VI-TR.55, Secu,d !':,1., June !!186)
STATE DEPARTMENT OF HIGHWAY'S
AND PUBLIC TRANSPORTA~iON;'':' :
HYDRAULIC
'MANUAL ...
DECEMBER' 1985
TABLE 6, CONSTANTS FOR USE IN FORMULA I : b/(tc+d)e
2 year 5 year 10 year 25 year 50 year 100 year
COUNTY
e b d e b d e b d e b d e b d e b d
Chambers 0.789 69 8,2 0,753 66 7,4 0.742 76 7,4 0.727 83 7,4 0,711 87 7.4 0,690 85 8,2
Cherokee 0,793 61 '8.4 0,783 74 8.5 0°754 75 8,5 0,751 85 8.5 0,742 91 8.5 0.733 96 8,4
Childress 0,825 51 10.3 0,807 65 10,2 0,814 78 10,2 0,821 97 10.2 0,822 108 10.2 0.824 126 10,3
Clay 0,797 50 8,8 0.787 64 8,4 0,790 74 8,4 0,787 88 8.4 0.790 99 8,4 0.780 110 8,8
Cochran 0,829 42 9,8 0,840 60 9.5 0,782 57 9.5 0.802 70 9,5 0.813 83 9,5 0,824 100 9.8
Coke 0.773 37 8,4 0,766 51 9,3 0,777 65 9,3 0.778 77 9,3 0,787 91 9.3 0,779 98 8.4
Coleman 0,767 40 7,6 0.763 54 8.0 0.770 66 8,0 0,763 78 8,0 0,781 92 8.0 0.769 98 7.6
Collin 0,790 54 8,2 0,781 67 8.8 0.778 79 8,8 0,779 92 8,8 0,776 102 8.8 0,764 106 8,2
Collingsworth 0.833 53 10.8 0.821 68 10.5 0.822 81 10.5 0.837 102 10.5 0.825 110 10.5 0.839 135 10.8
Colorado 0.810 68 8.3 0.778 74 8.3 0.756 79 8.3 0.744 87 8.3 0.736 94 8.3 0.723 96 8.3
Comal 0.796 56 8.4 0.781 69 8.6 0.775 78 8.6 0.766 87 8.6 0.753 91 8.6 0.758 105 8.4
Comanche 0.776 45 7.5 0.770 59 7.8 0.765 68 7.8 0.773 83 7.8 0.769 92 7.8 0.763 101 . 7.5
Concho 0.760 38 7.8 0.752 50 :8.0 0.779 67 8.0 0.755 73 8.0 0.785 91 8.0 0.767 95 ' 7.8
Cooke 0.793 51 8.4 0.779 65 8.7 0.780 77 8.7 0.791 93 8.7 0.787 104 8.7 0.774 109 8.4
Coryell 0.790 52 7.7 0.774 66 8.5 0.777 76 8.5 0.774 89 8.5 0.761 95 8.5 0.758 103 7.7
Cottle 0.816 48 9.~ 0.799 61 9.8 0.805 75 9.8 0.81i 91 9.8 0.817 105 9.8 0.813 118 9 8
Crane 0,815 38 9,4 0,819 55 10.2 0,818 66 10,2 0.785 69 10,2 0,801 82 10,2 0,798 88 9 4
Crockett 0,790 40 9.0 0.791 56 9,3 0.781 63 9,3 0.782 74 9.3 0,777 82 9,3 0,775 90 9 0
Crosby 0,819 46 9,6 0.815 61 10,1 0.809 69 10,1 0,811 83 10.1 0,807 92 10.1 0.810 106 9 6
Culberson 0.810 31 8,9 0,851 53 10,8 0,831 58 10.8 0,814 62 10.8 0.818 72 10,8 0.828 84 8 9
Dallam 0,860 51 10,8 0.866 68 10.6 0,824 68 10.6 '0.846 90 10,6 0.872 111 10.6 0,840 108 10 8
Dallas 0.791 54 8,3 0.782 68 8,7 0.777 78 8.7 0.774 90 8,7 0.771 i~01 8,7.~ 0,~62..__1.Q~-'-'-'~-~.
Dawson 0,820 44 10.0 0.818 59 10,4 0,814 68 '-10~'--~0~---'7~ ..... i'~.'~"-d]'80'~' 86 ~0.4 0~/9~ 9~ 10.0
Deaf Smith ~ 0,847 48 10.7 0.844 60 9,3 0,794 61 9.3 0,831 82 9,3 0.837 94 9,3 0.830 107 10,7
Delta 0,788 54 8,2 0.783 68 9,1 0,775 77 9.1 0.770 89 9,1 0.759 94 9.1 0,753 100 8,2
Denton 0,789 51 8,0 0,777 65 8.5 0,779 77 8,5 0.781 90 8.5 0,780 102 8.5 0.769 107 8.0
DeWitt 0.810 65 8,9 0,785 75 8.7 0.758 78 8,7 0,758 90 8.7 0,747 96 8,7 0,739 102 8,9
Dickens 0.810 45 9.4 0,807 61 10.0 0.803 71 10.0 0,808 85 10.0 0.808 96 10,0 0.809 109 9,4
Dimmit 0,830 60 .9,6 0.806 74 9.4 0,795 82 9.4 0.783 94 9,4 0.781 105 9.4 0.779 113. 9.6
Donley 0,839 52 11.0- 0.832 68 10,6 0,825 79 10,6 0.836 96 10.6 0,823 103 10.6 0.845 12~ 11,0
Duv'al 0.826 70 8,8 0,802 79 9.2 0,781 84 9,2 0.772 94 9.2 0,755 98 9,2 0,750 104 8,8
Eastland 0.780 45 8,0 0,772' 58 7.8 0.771 69 7,8 0,772 81 7.8 0.775 9'2 7,8 0,770 101 8.0
Ector 0.812 39 9,5 0.821 56 10.5 0.816 65 10,5 0.789 68 10.5 0,802 82 10.5 0.800 89 9.5
Edwards 0.790 44 8,2 0,759 54 7,5 0.759 63 7,5 0.769 76 7.5 0,776 88 7,5 0,772 100 8,2
Ellis 0,798 56 8,4 0,788 71 8.8 0,777 79 8.8 0.771 91 8,8 0,766 98 8.8 0.760 105 8,4