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SUBJECT: Foothill Sanitary Landfill 12/93 <br /> Storm Drainage Calculations <br /> The inlet time used in determining the 100 year <br /> intensity was determined graphically using the inlet <br /> time nomograph included in the County design manual <br /> referenced earlier, and is duplicated in this appendix <br /> after the intensity-duration curve. <br /> Design Flow Rate: <br /> The landfill was divided into watershed areas that <br /> drain to ditches and downdrain pipes located on the top <br /> of the landfill. Other areas of the property that <br /> drain directly to the open ditches were divided in a <br /> similar 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 three <br /> outlets from the landfill property are shown on the <br /> worksheets that follow. <br /> The design flow rates for the ditches on top of the <br /> landfill and along the landfill's perimeter are also <br /> shown on the worksheets. These flow rates were <br /> computed for those areas where the flow rate would be <br /> at the maximum. <br /> The maximum flow rate for pipes alon the top of the <br /> landfill for a 100 year storm is computed to be <br /> approximately 76 cubic feet per second (see Area K <br /> ditch design worksheet) . All CMP pipes along the top <br /> of the landfill will be 21t1 in diameter, which at a 3 : 1 <br /> slope can handle 92 cubic feet per second. <br /> The design computations for the perimeter draiange channel <br /> that surrounds the landfill site are based on the following <br /> formula. <br /> V = 1. 486 R113 Slee <br /> n <br /> The perimeter drainage channels are trapezoidal-shaped <br /> with 2 : 1 side slopes, bottom width of 121 , depth of 3 , <br /> and slope of 0. 002 . The Manning's Coefficient used was <br /> 0. 03 . <br />