Laserfiche WebLink
dle runoff from the prep plant azea as well as from the main gravel operation. Map C-4 shows the <br />drainage azeas for the site in addition to all ditches, berms and ponds. <br />The worst case for runoff into Pond #2 is when the operation has recently crossed the previous ac- <br />cess road and has begun moving south. Although some runoff will be trapped in the pit, most will <br />make its way south through previous sumps and be delivered to Pond #2. This azea is approximately <br />78 acres. When the active pit is further south, more runoff will enter the pit, which does not represent <br />the worst case. Part of the area is previously disturbed and very gravelly. The CN for undisturbed <br />azeas is 74 and disturbed gravel is 70. The approximate average for the entire disturbed area is 72. <br />Due to a number of sediment sumps present in the basin, a ponding percent of 20% has been as- <br />signed. <br />The design calculations for Pond #2 aze shown below. <br />Design Volume Calculations <br />Sediment Pond #2 <br />Area (acres) 72.6 <br />Design Event 100 yr. storm <br />Design Precipitation 2.8 Calculated S <br />Average CN 72 3.88888888889 <br />Description Porous Gravel Topsoil <br />Piles <br />Calculated Runoff Volume (Q) 0.6918128655 <br />Calculated Runoff Volume (acre-ft.) 4.18546783626 <br />Ponding Percentage 20 <br />Actual Runoff Volume (acre/ft.) 334837426901 <br />As shown on Map C-2, Pond #2 is 1.15 acres in surface azea, therefore, its required depth is 2.9 feet <br />to hold 3.34 acre feet. It will be constructed to 3.3 feet deep and 2H:1 V sideslopes. All other ponds <br />will use similaz slopes. <br />Alma Placer 7/03 15 <br />