2009-10-16_PERMIT FILE - M2009082 (13)

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Parsons Mine Lafarge West, Inc Preliminary Drainage Report 'Peak Runoff Calculations Using the Rational'Method Basin: P9-1 (H8) Condition: Developing Storm Retum Period: Basin Chracteristics Area, A 11.4 acres Basin Imperviousness' (in percent), is 15.0'0 Distance of Overland Flow, L„ 0 ft Hydrologic Solis Group A Percent of Basin: 2.94b Distance of Channelized Flow, Lt: 3.710 ft Hydrologic Soils Group B Percent of Basin: 84.5% Average Basin Slope, S: 0.01029 ftlft Hydrologic Soils Groups C,& D Percent of Basin: 126% Slope of Channelized Flow, S;: 0.00095 ft/ft Conveyance Coefficiens , C,,: 10 Runoff Coefficient,. Runoff Coefficient Equations For 100-yrStorm Return Period: KA = -0.25i + 0.32 C,,=K, + (1. 3113 -1.44i2 + 1.135i - 0.12) for CA a b elwc,=,O K? _ -0.391 + 0.46 C?=K + (0:8581' - 0.78(112 + 0.7741'+ 0:04) For 10-yr Storm Return Period' KA = -0.141 + 0.17 CB=(CA + Cm) / 2 KcD = -0.18i + 0.21 For 5-yr Storm Retum Period: KA = -0.08i + 0.09 Return Period C?;P-1e Cr, CB Cco KA KcO 5-Year 0.175 0.100 0.168 0.236 0.07$ 0.095 10-Year 0.255 0.171 0.248 0.324 0.149' 0:183 100-Year 0.435 0.305 0.424 0.543 0.283 0:402 K?=-0.10i+0.11 Time of Concentration Rainfall Intensity 71 Total time of concentration equation Rainfall Intensity Emation: Lesserof3: t? t, + t, 1=(28.5 ' Pu.)./ (10 + TJ°'786 where PjM is the 1 hr point rainfall depth or t,=L / 180 +10 (if in urban area) Overland flow travel time equation. V 212 min t;=(0.395: (1.1 CS)' sgrt(L.)) / So.a3 _ 0 min _Qhannelized flow travel time equation: tt= 212 min 4=L,1(V' 60) where V= (C„ • SWos) V= 4.292 ftis P1h Return Period In in / hr 5-Year 1.49 0.61 10-Year 1.76 0.72 100-Year 2.78 1.13 Peak Flow Rate Rational Method Equation Q=Ca'I A Return Period Co_?_ne ? in / hr q acres Q CfS 5-Year 0.175 0.61 11. 1.2 10-Year 0.255 0.72 11.4 2.1 100-Year 0.435 1.13 11.4 56 Notes: 1: Basin imperviousness determined from guidelines in UDFCD Drainage Criteria Manual Table RO-3 2: Conveyance coefficierWdetennined 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: 9/1712009