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SUBJECT: Foothill Sanitary Landfill 3/95 <br /> Storm Drainage Calculations <br /> The inlet time used for an area in determining the 100 <br /> year intensity was determined by dividing the length of <br /> the longest flow path within an area by an assumed <br /> initial velocity of 2 feet per second, and then <br /> converting the time to minutes. <br /> Design Flow Rate: <br /> The landfill was divided into watershed areas that drain <br /> to ditches and downdrain pipes located on the top of the <br /> landfill. other areas of the property that drain <br /> directly to the open ditches were divided in a similar <br /> fashion. <br /> The individual watersheds and the respective areas are <br /> shown on the Drainage Area Designations figure included <br /> in this appendix. The design flow rates for the <br /> landfill's perimeter ditches are shown on the worksheets <br /> that follow. The actual computed 100 year storm event <br /> flow rates within the perimeter ditches are shown on the <br /> Storm Design Sheets that follow. <br /> The flow rates computed for each area were computed at <br /> the areas' discharge point into a pipe or the next area <br /> in the chain, which is where the flow rate would be at <br /> the maximum. <br /> The respective maximum computed flow rates for pipes <br /> along the top of the landfill for a 100 year storm are <br /> shown on the Individual Area Drainage Design Data <br /> worksheet. The worksheet also shows the respective pipe <br /> size for each area along the top of the landfill. A 3 : 1 <br /> slope was used for computing each area's pipe size. <br /> The design computations for the perimeter drainage channel <br /> that surrounds the landfill site are based on the following <br /> formula. <br /> V = 1.486 A"' S1r2 <br /> n <br /> The perimeter drainage channels are trapezoidal-shaped <br /> with 2 : 1 side slopes, a bottom width of 121 , and slope of <br /> 0. 002. The depth varies according to the maximum flow <br /> rate. The Manning's Coefficient used was 0. 03 . <br /> R: \WES\EN\FH\CLOSE\RESPOND.LET <br /> LA 31581 <br />