Laserfiche WebLink
Precipitation and Storm Type. The precipitation amounts at the Seneca II-W Mine permit <br />area for the 10-year, 25-year end 100-year storms were obtained from NOAA Precipitation <br />Frequency Atlas Precipitation - Frequency Atlas of the Western States - Volume II - <br />Colorado, 1973. A standard SCS Type fl storm was utilized for each analysis. <br />a <br />Unit Nydrograph and Surface Condition. The SEDCAD computer program provides three unit <br />hydrograph shapes to choose from in determining the runoff characteristics of a watershed. <br />Time of Concentration. The time of concentration, tc, is defined as the time required for <br />water to flow from the hydraulically most remote point in the watershed [o the watershed <br />outlet. <br />i <br />The time of concentration for Pond 006 was calculated using the SEDCAD computer program. <br />The program determines overland flow to a pond structure by utilizing the seven SCS Upland <br />Curves which yield velocity es a function of slope end land use. Listed below is a <br />summary of the time of concentration for the subwatersheds. <br />land Flow Vertical Horizontal Slope Velocity Time <br /> <br />Condition <br />_Dist (ft) <br />Dist (ft) <br />(~Z <br />(fps) • <br />(Nr) <br /> <br />2 205.0 1560 73.14 1.81 0.239 <br />6 270.0 2720 9.93 4.73 0.160 <br /> Total time of concentration SWS-1 0.399 <br />3 200.0 1200 76.67 2.86 0.117 <br />8 30.0 600 5.00 6.77 0.025 <br />6 302.0 3160 9.56 4.64 0.189 <br /> Total time of concentration SWS-2 0.331 <br />3 112.0 950 17.79 2.40 0.110 <br />8 90.0 7720 5.23 b.Bb 0.070 <br />6 355.0 2400 14.79 5.77 0.116 <br /> Total time of concentration SWS-3 0.295 <br />3 63.0 1700 3.71 1.35 0.350 <br />5 370.0 2680 13.81 3.72 0.200 <br />7 250.0 2720 9.19 6.10 0.724 <br /> Total time of concentration SWS-4 0.675 <br />• <br />12 <br />