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Parsons Mine - Lafarge West, Inc <br />Preliminary Drainage Report <br />Peak Runoff Calculations Using the Rational Method <br />Basin: RB2-7 (HI) Condition: Reclaimed Storm Return Period., <br /> <br /> Basin Chracteristics <br />Area, A 45.G acres Basin Imperviousness` (in percent), is 2.0% <br />Distance of Overland Flow, Lo: 2,793 fL. Hydrologic Soils Group A Percent, of Basin: 1.0 <br />Distance of Channelized Flow, Lt 0 ft Hydrologic Soils Group B Percent of Basin: 71.5°/ <br />Average Basin Slope, S: u.OW94 ft/ft Hydrologic Soils Groups C &D Percent of Basin: 27.6% <br />Slope of Channelized Flow; SW: ft/ft Conveyance Coefficient2, C,,: 5 <br /> <br /> Runoff Coefficient <br />Runoff Coefficient Equations For 100-yr Storm Return Period: KA = -0.25i + 0.32 <br />CA-Kn + (1.31i'- 1.44i2 + 1:135i - 0,12) for C„2 0 else CA -'0 ' K,-o = -0.39i + 0.46 <br />Cco=Kco + (0.8583 - 0,786i2<+ 0.774i + 0.04) For 10-yr Storm Return Period: KA =-0.14i+0.17 <br />CB=(CA + Cco) LZ <br /> KBD `-0.18i +0.2r <br /> For 5-yr Storm Return Perod: ; KA _ -0.08i + 0.09 <br />Return Period C'OMPG Ie CA CB CCD Kn Kce <br />5-Year 0.103 0.000 0.082 0.163 0.088 0.108 <br />10-Year 0.191 0.069 0.165 0.262 0.167 0.206 <br />100-Year 0.401 0.217 0.362 0.507 0.315 0.452 <br />Kco - -0.101 + 0.11 <br />Time of Concentration Rainfall Intensity <br />Total time of concentration a uationi Rainfall Intensity Equation <br />Lesser of : tit + t( 1=(28.5 - P,,,,) / (10 + Tjo 786 where P,,,, is the 1 hr point rainfall depth <br />or t,=L / 180 +10 (if in,urban ,area) <br />Overland flow travel time eauatiow te= 95 min <br />t=(0.395 (1,1 - Cs) " sgrt(L,)) I50.33 4= 95 min <br />Channelized flow travel time equation: t,= 0 min <br />4=L. / (V ' 60) where V= (Cv . Swos) V 0.000 ft/s <br /> P, r, <br />Return Period in in hr <br />5-Year 1.49 1.09 <br />10-Year 1.76 1.29 <br />100-Year 2.78 2.04 <br />Peak Flow Rate <br />RRitional Method Eciuafion: <br />Q = CrAmposu . q <br />CC-9--ft- 1 A <br />Ret <br />in / hr <br />acres <br />CfS <br />E 0.103 1.09 45.0 <br /> 0.191 1.29 45.0 <br /> 0.401 2.04 45.0 36.9 <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 t1DFCD Drainage Criteria Manual Table RO-2 <br />3: Minimum t. is 10 min. for non-urban areas and 5 min. for urban areas Date: 9/1812009