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CALCULATION OF A PEAK RUNOFF USING RATIONAL METHOD <br />Project Title: <br />Catchment ID: <br />1. Catchment Hydrologic Data <br />Catchment ID = A <br />Area = 38.00 Acres <br />Percent Imperviousness = 2.00 % <br />NRCS Soil Type = C A, B, C, or D <br />II. Analysis of Flow Time (Time of Concentration Tc) for a Catchment <br />Tc = To + Tt <br />To = 1.8(1.1 - CS)I, `/ S,is <br />Avg. slope for longest watercourse S = 0.29 % <br />Runoff Coefficient for 5 Year Storm C5 = 0.20 <br />Distance of overland flow L = 400 feet <br />To = 49 minutes <br />Tt= L/60V <br />Velocity of Flow V = 3.5 fps <br />Length of channel L = 1,200 <br />Tt = 6 minutes <br />TC= 55 minutes <br />III. Rainfall Information <br />Serfer Pit <br />A <br />Design Storm <br />Return Period <br />(years) I (inch/hr) --Per <br />Figure 3-1 <br />2 year 1.00 <br />100 year------ --------- ----2.81 <br />IV. Peak Runoff Prediction Q = CIA <br />Basin Area (acres) A= 38.00 <br /> C I Q <br />Design Storm Runoff Coefficientfor (inch/hr) PEAK <br />Return Period flat, pasture/range per the OF curve for FLOWRATE <br />(years) land the mining site (CFS) <br />2 year 0.20 1.00 7.6 <br />100 year 0.60 2.81 64.1