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0 FORWARD LANDFILL <br />C7 <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 />Where <br />Q = CIA <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 />I = 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 />rainfail intensity '(i) foT-astorm 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:\AI li ed\2000.1 9 3\Report\finaljtd:forward-hyd:08/20/01 <br />