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Parsons Mine - Lafarge West, Inc <br />Preliminary Drainage Report <br />Peak Runoff Calculations Using the Rational Method <br />Basin: P1-9,(1-19) Condition: Developing Storm Return Period: <br /> <br /> Basin ChMiateristics <br />Area, A 1.4 acres Basin imperviousness) (in percent), is 0 0-/0 <br />Distance of Overland Flow, Lb 36 ft Hydrologic Soils Group A Percent of Basin: 0.0% <br />Distance of Channelized Flow, L,: 0 ft Hydrologic Soils Group B Percent of Basin: 56.3'1 <br />Average Basin Slope, S: 0.01650 ft/ft Hydrologic'Soils Groups,C & D Percent of Basin: 43.7% <br />Slope of Channelized Flow, SW: Wit Conveyance Coefficiene, C,: 10 <br /> <br /> Runoff Coefficient <br />Runoff Coefficient Equations For 100-yr Storm Return Period: KA = -0.25i + 0.32 <br />C,=K„ + (1.31 i3 = 1.44i' + 1.135i - 0.12) for CA z 0 else CA = 0KcD = -0.391 + 0.46 <br />Cr,=Koo + (0.858i3 - 0.78612 + 0.774i+ 0 .04) For 10-yr Storm Return Period: KA = -0.14i + 0.17 <br />C7=(CA + CcD) / 2 <br />...KcD = -0:181 + 0.21 <br /> For 5-yr Storm Return Period: KA = -0 <br />:081 + 0:09 <br /> KcD = -0:101 + 0.11 <br /> Return Period C.m.sue' C CB Cm KA KcD <br /> <br />5-Year 0.108 0.000 0.075 0.150 0.090 0.110 <br />10-Year 0.194 0.050 0.150 0:250 0.170 0.210 <br />100-Year 0.416 0.200 0.350 0.500 0.320 0.460 <br />Time of Concentration Rainfall Intensity <br />Total time of concentration equation: Rainfall Intensity Equation? <br />Lesser of3: t?=t{ + t, 1=(28.5 ` P11 (10 + Tj17°s where P1hr is the 1 hr point rainfall depth <br />or t,=L / 180 +`10 (if in urban area) <br />Overland flow travel time equation: t<= 9' min <br />t;=(0.395 • (1.1 - C5) ' sgrt(L.)) / S033 9 min <br />Channelized flow travel time equation: 4= min <br />t =4 ! (V ' 60) where V= (C„ • Swos) ` V= 0.000 ft/s <br /> P01 <br />Retum Period in in / hr <br />5-Year 1:49 410 <br />10-Year 1.76 4.96 <br />100-Year 2.78 7.83 <br />Peak Flow Rate <br />Rational Method Eauationi <br />Q=Ca'f?A <br />Return <br />Period C?«;,?f1e 1 <br />in/hr T A <br />acres Q ' <br />CfS <br />5-Year 0.108 4.20 1.4 0.6 <br />10 Year 0.194 4.96 1.4 1.4 <br />100-Year 0.410 , 7.83 1. 4, 4.6 <br />Notes: <br />1: Basin imperviousness determined from guidelines in UDFCD Drainage Criteria Manual Table RO-3 <br />2: Conveyance coefficient determined from guidelines inLIDFCD Drainage Criteria Manual Table RO-2 <br />3: Minimum t, is 10 min. for non-urban areas and 5 min. for urban areas Date: 9117/2009