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A CN of 67 is assigned to the gravel since it is nearly void of fines and almost all runoff penetrates <br />into the ground. This pond has a surface azea of 0.14 acres therefore, its required depth is 1.0 feet. It <br />will be dug 2.0 feet deep with 2H:1 V sideslopes. <br />Willits Pond #6 handles the runoff from the northern part of the mining azea. This azea is6.2 acres. <br />•~ <br />The calculations to demonstrate that this pond is adequate to contain the 100 year 24 hour event aze <br />shown below: <br />Design Volume Calculations <br />Willits Pond #5 <br />Area (acres) 6.2 <br />Design Event 100 yr. storm <br />Design Precipitation 2.8 Calculated S <br />Average CN 67 4.92537313433 <br />Description Porous Gravel <br />Topsoil Piles <br />Calculated Runoff Volume (Q) 0.4886955832 <br />Calculated Runoff Volume (acre-ft.) 0.25249271799 <br />Ponding Percentage 5 <br />Actual Runoff Volume (acre/ft.) 0.23986808209 <br />A CN of 67 is assigned to the gravel since it is neazly void of fines and almost all runoff penetrates <br />into the ground. This pond has a surface azea of 0.19 acres therefore, its required depth is 1.26 feet. <br />It will be dug 2.0 feet deep with 2H:1 V sideslopes. <br />Willits Ponds #4, #5, and #6 have collection ditches which feed them at the toe of the disturbed <br />azeas. These ditches will be dug in gravel so they need no lining and they will be dug to 1.5' depth <br />with 2H:1V sideslopes. <br />Alma Placer 7/03 <br />28 <br />