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: P1=7 (H8) & P1--8 (H9) Condition: Developing Storm Return Period:

Basin Chracteristics
Area, A 9.5 acres Basin Imperviousness (in percent), is 15.0%
pistance of Overland Flow, L, 0 ft Hydrologic Soils Group A Percent of Basin: 1.7%
Distance of Channelized Flow, L, 1,651 R Hydrologic Soils Group B Percent of Basin: 72.6%
Average Basin Slope, S: 0.01028 ft%ft 'Hydrologic Soils Groups C & D Percent of Basin: 25.7%
Slope of Channelized Flow, SW,: 0.01162 ft/ft Conveyance Coefficiene, C,:' 10

Runoff Coefficient
Runoff Coefficient Equations For 100-yr Storm Return Period: KA _ -0.251 + 0.32
CA=KA + (1.311 1.44i2 + 1.135i - 0.12)»forCq 0 else'CA= O Kcp = -039i + 0.46
C,-,)=Kcp + (0.858i3 - 0.786i2 + 0.774i + 0.04) _ For 10-yr Storm Return Period: KA - -0.14i + 0.17
CB=(C'A + Cco)/2 Kc _ -0.18i + 0:21 .
For 5-yr Storm Return Period: KA = -0-08i + 0.09
Kr„=-0.10i+0.11
Return Period Co Pi ile CA CB CCD KA Koo
5-Year 0.185 0.100 0.168 0.236 0.078 0.095
10-Year 0.266 0.171 0.248 0.324 0.149 0.183-
100-Year 0.452 0.305 0.424 0.543 0.283 0.402
Time of Coricentration Rainfall Intensit
Total time of concentration eauationt Rainfall Intensity Equation:
Lesser of : t,=t; + t, 1=(28.5 • P,,) /.(10 + T,)0786 where Pit„ is the 1hr point rainfall depth
or t,=L / 180 +10 (if in urban area)
Overland flow travel time equation: t?= 29 min
4=(0.395- (1.1 - Ce) * Sgrt(L.)) / SO-33
$- 0 min
Channelized flow travel time equation: 4= 29 min
4=L, / (V 60) where V= (C, ' S,'-S) V= 1.078 ft /s

Pin.
Return Period in In / hr
5-Year 1.49 2.38
10-Year 1.76 2.82
100-Year 2.78 4.45
Peak Ffnw Rata
Rational Method,Eau6bon:
.A .
Return
Period i
in / hr A
acres Q
CfS
5-Year 0.185 2.38 9.5 4.2
10-Year 0.266 2.82 9.5 7.1
100-Year 0.452 4.45 9.5 19:2
Notes:
1: Basin imperviousness determined from guidelines in UDFCD Drainage Criteria Manuai Table RO-3
2: Conveyance coefficient determined' from guidelines in UDFCD Drainage Criteria ,Manual Table RO-2
3: Minimum t, is 10 min. for non-urban areas and 5 min. for urban areas Date: 9117/2009