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: P1-12 (149) Condition: Developing Storm Retum Period.

Basin Chracterstics
Area, A 2.1 acres Basin Imperviousness' (in percent), is 50%
'Distance of Overland Flow, Lo: 3 9 ft Hydrologic Soils Group A Percent of Basin: 0.0%
Distance of Channelized Flow, L.: 0 ft Hydrologic Soils Group B Percent of Basin: 56,3%
Average Basin Slope, S O01650 ft/ft Hydrologic Soils Groups C & D Percent of Basin: ` 43.7°/,
Slope of Channelized Flow, SW: ftift Conveyance Coefficient, C,: 7

Runoff Coefficient
Runoff Coefficient Equations For 100-yr Storm Return Period: KA = -0.251 + 0.32
CA=KA+(1:31i3-1.44i2+1.1351-0.12) forCAz0else CA=O. KcD =-0.391+0.46
Cce=K,, + (0.858i3 - 0.786i2 + 0.774i + 0.04) For 10-yr Storm Return Period: K, = -0.141 + 0.17
Ca=(C'A + Cco) / 2
Kco=-0.181+0.21
For 5-yr Storm Return Period: KA _ -0.08i + 0.09
K__=-nl'ni+n
Return Period C ?y,e CA CB Cco KA Kcv
5-Year 0.136 0.019 0.101 0.182 0.086 0.105
10-Year 0.227 0.096 0.187 0.278 0.163 0.201
100-Year 0.439 0.241 0.379 0.517 0.308 0.441
Time of Concentration Rainfall Intensity
Total time of concentration equation: Rainfall Intensity Eauation:
Lesser of': Vii + 4 1=(28.5 P„„) / (10 + T.)07'6 where PIN is the 1 hr point rainfall depth
or t,=L / 180 +10 (if in urban area)
Overland flow travel time equation: V 27. min
4=(0395 ' (1.1 - C5) - sgrt(Lo)) / So.a3 4= 27 min
Channelized flow travel time equation: 1<= 0 min
ti=,L, / (V • 60) where v= (C„ • Swos) v= 0.000 ff/s
P,n
Retum Period in in / hr
5-Year 1A 2.49
10-Year 1.76 2:94
100-Year 2.78 4.64
Peak Flow Rafe
Rational Method Equation:
Q=C ;w•1*:A
Return
Period C, I
in / hr A
acres Q
CfS
5-Year 0.136 2.49 2.1 0.7
10-Year 0227 2.94. 2.1 1.4
t00-Year 0.439 4.64 21 4.3
Notes:
1: Basin imperviousness determined from guidelines in UDFCD Drainage Criteria Manual Table RO-3
2: Conveyance coefficient determined from guidelines in UDFCD Drainage Criteria Manual Table RO-2
3: Minimum tc is, 10. min. for non-urban areas and 5 min. for urban areas Date: 9/17/2009