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EOSYNTEC CONSULTANTS Page 2' of Written by: JOE TAM Date: 22 -Oct -99 Reviewed by: Date: Client: Allied Waste Project: Forward Landfill Project/Proposal No.: WS0264 Task No.: 01 A= cross-sectional area of flow (ft) R = Hydraulic radius (ft) = A/P P = Wetted perimeter (ft) So = Longitudinal slope of channel (ft/ft) The erosion resistance of the ditch linings is evaluated by comparing the peak flow velocities during the design storm to typical maximum allowable velocities of 2 ft/s or less for grass -lined ditches. Culverts and Downchutes Culverts are designed to handle the peak discharge from the 100 -year, 24-hour storm, in accordance with California regulations for Class III landfills [Table 4-1 of Title 27, CCR]. Culverts are designed to flow under inlet control conditions (i.e., super -critical flow in the culvert), which minimize the amount of sediment deposited in the culverts during storm events. Culvert nomographs [AISI, 1994] are used to predict the maximum headwater depth at culvert inlets for inlet control flow. There are three groups of culverts at the Forward Landfill: 1) side slope downdrains, 2) east area perimeter drains, and 3) south area perimeter drains. The side slope down drains are oriented on the slope of the landfill, running from the edge of the crown to the toe. The east area drains run alon the eastern toe, and the south area drains run along the southern toe. The down drain pipes are sized handle the design flow rates with a maximum headwater depth of 1.5D at the berm along the top deck o the landfill, and 1D at the benches (D = diameter of the culvert), i.e. no greater than the diameter of the culvert. The culverts at the eastern and southern toe of the landfill are sized for a maximum headwater depth of 1D. MALLIEDWASTE\FORWARD WMU B\CLOSURE PLAN\DRAINCALCS\SW2.DOC