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Parsons Mine - Lafarge West, Inc <br />Preliminary Drainage Report <br />Peak Runoff Calculations Using the Rational Method <br />Basin: H5 Condition: Existing Storm Retum Period. <br /> <br /> Basin Chracteristics. <br />Area, A: 28.2 acres Basin Imperviousness' (in percent), I: 0.0% <br />Distance of Overland Flow, L9: 1,061 ft Hydrologic Soils Group A Percent of Basin: 12.3% <br />Distance of Channelized Flow, LY: 0 tt Hydrologic Soils Group B Percent of Basin: 0.0°0 <br />Average Basin Slope, S: 0.00067 ftifC Hydrologic Soils Groups C & D Percent of Basin: 87.7% <br />Slope of Channelized Flow, Sw ft/ft Conveyance Coefficient2, C,,: 5 <br /> <br /> Runoff Coefficient <br />Runoff Coefficient Equations For 100-yr Storm RetumPeriod: KA = -0.25i + 0.32 <br />CA=KA + (1.31 i3 - 1.44i2 + 1.1351- 0.12) for CA ? 0 else CA = O KcD _ -0:39i + 0.46 <br />Cco=lCcp + (0.85813 - 0.786i2 + 0:774i +-0.04) For 10-yr Storm Retum Period: KA = -0.14i + 0.17 <br />CB=(CA + Cco) ! 2 KcD = =0.181 + 0.21 <br /> For 5-yr Storm Return Period. KA = -0.081 + 0.09 <br /> fC - 010 +01 <br />Return Period C-,, ,i, C. C. C. KA KGD <br />5-Year 0.132 0.000 0.075 0.150 0.090 0.110 <br />10-Year 0.225 0:050 0.150 0.250 0.170 0.210 <br />100-Year 0.463 0.200 0.350 0.500 0.320 0.460 <br />CD --1 <br />Time of Concentration, Rainfall Intensity <br />Total time of concentration equation: Rainfall Intensity Equation: <br />Lesser oP: tc=t, + i< 1=(28.5 ' Pjj / (10 + T?f r86 where Pl,; is the 1hr point rainfall depth <br />or t,=L / 180 +10 (if in urban area) <br />Overland flow travel time equation: tc= 139 min <br />t,=(0.395 - (1:1 - CS) ' sgrt(L.)) / SOM t,= 139 min <br />Channelized flow travel time equation: ti= 0 min <br />1=L, ! (V `60) where V= (C, • SW 05) V=, 0.000 ft/S <br /> PAM <br />Return Period In inJ hr <br />5-Year 1.49: 0.83 <br />10-Year 1.76 0.98 <br />100-Year 2.78 1.55 <br />Peak Flow Rate <br />Rational Method Equation: <br />Q =Cco pos to I A <br />Return <br />Period Cam, I <br />in hr A <br />acres Q <br />CfS <br />5-Year 0.132 <br />0.83. <br />•28.2 <br />3.1 <br />10-Year 0.225 0.98 28.2 6.2 <br />100-Year 0.463 1.55 28:2 2 <br />Notes: <br />1: 3a "sin imperviousness determined from guidelines in UDFCD Drainage Criteria Manual Table RO-3 <br />2: Conveyance coefficient determined from guidelines in UDFCD Drainage Criteria Manual Table RO-2 <br />3: Minimum t. is 10 min. for non-urban areas and 5 mina for urban areas Date: 9117/2009