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® FORWARD LANDFILL <br /> A hydrology study for the site was conducted in accordance with Title 14, Section <br /> 17778 and Title 23, Section 2546 and utilizing San Joaquin County local rainfall data <br /> to calculate runoff flows. In calculating 100-year runoff peak discharges, a computer <br /> program developed by Advance Engineering Software (AES) was used. <br /> In performing the drainage study, the Rational Method was utilized. The rational <br /> method was originally developed to estimate runoff from small (less then one square <br /> mile) urban and developed areas and its use should be limited to those conditions. <br /> Basically, the rational method equation relates rainfall intensity, a runoff coefficient, <br /> and drainage area size to the direct peak runoff from the drainage area. This <br /> relationship is expressed by the equation: <br /> Q = CIA <br /> Where <br /> Q = the runoff in cubic feet per second (cfs) from a given area <br /> C = a runoff coefficient representing the ratio of runoff to rainfall <br /> 1 = the time-averaged rainfall intensity in inches per hour <br /> corresponding to the time of concentration <br /> A = drainage area (acres) <br /> The values of the runoff coefficient (C) and the rainfall intensity (1) are based on a <br /> study of drainage area characteristics such as type and condition of the runoff <br /> surfaces and the time of concentration. These factors and the limitations of the <br /> rational method equation are discussed below. Drainage area (A) may be <br /> determined by planimetering a suitable topographic map of the project area. <br /> Data required for the computations of peak discharge by the rational method are: (i) <br /> rainfall intensity (1) for a storm of specified duration and selected design frequency; <br /> (ii) drainage area characteristics of size (A), shape, slope; and (iii) a runoff coefficient <br /> (C). Rain fall and hydrology data from the local rain gage station were utilized. <br /> Hydraulic Calculations <br /> The drainage structures proposed for this project are sized to accommodate the <br /> calculated flows from the hydrology study. The Mannings equation for normal <br /> depth, open- channel flows was used to verify the capacity of channel sizes. <br /> L:\Allied\2000.193\Report\fi naljtd:forward-hyd:08/20/01 1 <br />