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Parsons Mine -Lafarge West, Inc <br />Preliminary Drainage Report <br />Peak Runoff Calculations Using the Rational,Method <br />Basin: H7 'Condition: Existing Storm Retum Period: <br />Basin -Chracteristics <br />Area, A 21.7 acres Basin Imperviousness' (in percent), is 0 "t <br />Distance of Overland Flow,,L,: 1,300 ft Hydrolo&,Soils Group A Percent of Basin: 65.1 % <br />Distance of Channelized Flow, 4: 0 ft <br />Hydrologic Soils Group B Percent of Basin: 34.4% <br />Average Basin Slope, S: 0.00421 ft/ft Hydrologic Soils Groups C & D`Percent of Basin: 0.6% <br />Slope of Channelized Flow, S..: ft/ft Conveyance Coefficient2, C,: 5 <br />Runoff Coefficient <br />Runoff Coefficient Equations For 100-yr Storm Return Period: KA = -0.251 + 0.32 <br />CA-KA +' (1.31 i3 -1.44i2 + 1.135i - 0.12) for CA z 0 else CA = 0' K cj) = -0.391 t 0.46 <br />C?=Kco + (0.858i3 - 0.786i2 + 0.774i + 0.04) For 10-yr Storm Return Period. KA _ -0.14i + 0.17 <br />Ce=(CA + Cco) / 2 <br />Kco = -0:181 ± 0,21 <br />Fors-yr Storm-Return Period:- KA _ -0.081 + 0:09 <br />K --010'+011 <br />Return Period Ccompo to CA C. Cco KA K. <br />5-Year 0.027 0.000 0.075 0.150 0.090 0:110 <br />10-Year ' 0.086 0:050 0.150 0.250 0.170 0.210 <br />100-Year 0.254 0:200 0.350 0.500 0.320 0.460 <br /> <br />Time of Concentration Rainfag Intensity <br />Total time of concentration equation <br />Lesser of 4=t + t, <br />or t,=L 1 180 +10 (if in urban area) <br />Overland flow travel time equation: tc= 93 min <br />4=(0.395',(1:1-CS).sgrt(L,))/So.3a C 93 min„ <br />Channelized flow travel time equation 4= 0 min <br />4=t., / (V • 60) where V= (C„ • SW' )' V= .0.000 ftis <br />Rational Method'Eguadon: <br />Q= Ccomposta ` I ' A <br /> PzM <br />Return Period in in/ hr <br />5-Year 1.49 1.11 <br />10-Year 1:76 1131 <br />100-Year 2.78 2.07 <br />Return <br />Period Cwnprits I <br />in I hr. A <br />acres Q <br />CfS <br /> 0.027 1.11 21.7 0.6 <br />ff(O?Year 0.086 1.31 21.7 2.4 <br /> 0.254 2.07 21.7 11.4 <br />Notes: <br />1: Basin 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 min. for urban areas Date: 9/1712009 <br />Rainfall Intensity Equation: <br />I=(28.5' Ptik) /116 + Tj" where P,,, is the 1 hr point rainfall depth <br />