2009-10-16_PERMIT FILE - M2009082 ‎(13)‎

• Permit No: M2009082
• IBM Index Class Name: PERMIT FILE
• Doc Date: 10/16/2009
• Doc Name: Attachment G-4, Preliminary Drainage Report
• From: Lafarge West, Inc.
• To: DRMS
• Media Type: D
• Archive: No

Parsons Mine - Lafarge West, Inc
Preliminary Drainage Report
Peak Runoff Calculations Using the Rational Method
Basin P?-2 (H8) Condition: Developing Storm Return Period:
Basin Chracteristics
Area, A: 27 acres Basin Imperviousness' (in percent), is 15.0°0
Distance of Overland Flow, Lo: 0 ft . Hydrologic Soils Group A Percent of Basin: ` 2.9"'
Distance of Channelized Flow, L.: 1,395 ft- Hydrologic Soils Group B Percent of Basin: 84.5%
Average Basin Slope, S 0.01028 ft/ft Hydrologic Soils Groups C & D Percent of Basin: 12.6%
Slope of Channelized Flow, S,,,: 0.00212 Will Conveyance Coefficient2, C,: ; 10
Runoff Coefficient
Runoff Coefficient Equations `For 100-yrStorm Return Period: KA = -0.25i + 0.32
CA=KA + (1.31 i3 - 1.4412 + 1.1351 0.12). for CA z 0 else CA= 0 KcD = -0.39i + 0,46
Cco=Kco + (0.85813 - 0.786i2 + 0.7741,+ 0.04) For Rl-yr Storm Return Period: KA = -0.141 + 0.17
Ca=(CA + CCD) / 2
Kco =-0-181 +0.21
For 5-yr Storm Return Period: KA = -0.08i + 0.09
K
Return Period Cam,,, w CA C. Co KA Kco
5-Year 0:175 0.236 0.078 0.095
10 Year 0:255 = 0.324 0.149 0.183
100-Year 0.435 0 0.424 0.543 0.283 0:402
CD --0.IW U.11
Time of Concentration Rainfall Intensity
Total time of concentration equation: Rainfall Intensity Equation-
Lesser of : t,=t; + t, 1=(28.5 - P,,) / 10 + T o'er where Pp, is the 1 hr
in) ( ?) ?r? point rainfall depth
or t,=L / 180 +10 (if in urban area)
Overland flow travel time eguatiom tc= 51 min
t=(0.395 - (1.1 - C5) ' sgrt(L.o)) / S0.33 _ p min
Channelized flow travel time equation: 4= 51 min
4=Lc / (V ' 60) where V= (C„ - S,,,os)' V 0.460 ftis
P,? 1
Return Period in in/hr
5-Year 1.49 1.68
10-Year 1.76 1.98
100-Year 2.78 3.13
Peak Flow Rate
Rational Method Eauation-_
Q C?? ' l ! A
Return
Period CW-p- I
in / hr A
acres Q
efs
5-Year 0.175 1.68 2.7 0.8
10-Year 0.255 1.,98 2.7 1.4
100-Year 0.435 3.13 2.7 .3.7
Notes:
1: Basin imperviousness determined from guidelines in UDFCD-Drainage Criteria Manual Table RO-3
2: Conveyance coefficient determined ;from guidelines in UDFCO, Drainage Criteria Manual Table RO-2
3: Minimum:t, is 10 min. for non-urban areas and 5 min. for urban areas Date: 911712009