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<br />DRAFT <br /> <br />all sub catchments can be routed through a maximum of 399 gutters <br />or pipes to compute hydrographs at the inlet points. Overbank <br />floodway sections may be used in conjunction with gutters and <br />pipes. Up to 25 detention basins with specified storage-outflow <br />relationships may be used. Also, the program allows the user to <br />specify a flow diversion table for up to 25 routing elements. The <br />core of the runoff block is the routing of hydrographs through the <br />drainageway system. This is accomplished by a combination of <br />overland flow and channel, gutter, reservoir and pipe routing. <br /> <br />Two types of elements are simulated: <br /> <br />1. Subcatchment elements (overland flow) <br />2. Conveyance elements (channel flow, <br />pipe flow, storage, etc) <br /> <br />The subcatchment elements receive rainfall, account for <br />infiltration loss using Horton's equation, permit surface storage <br />such as ponding or retention on grass or shrubbery, and route <br />excess rainfall to develop overland flows. The overland flows are <br />then routed through the conveyance elements of the watershed. <br />Pipes and initial channel sections are permitted to surcharge when <br />full or, if desired, overflow sections may be provided to convey <br />the flow exceeding the pipe or the initial channel capacity. The <br />routing is based on a kinematic wave approach utilizing Manning's <br />equation both for subcatchment and conveyance elements. <br /> <br />Data <br /> <br />Data requirements for UDSWM2 are similar in nature to HEC-l, <br />although the form of data is different. The basic category of data <br />inputs are: drainage system geometry, flow resistance, rainfall <br />loss parameters and rainfall. Descriptions of the parameters used <br />and the sources from which they were derived are presented in the <br />following paragraphs. <br /> <br />Drainage System Geometry <br /> <br />Watershed geometry involves the delineation of the drainage system <br />into a network of overland flow units from which runoff is <br />generated and a receiving system of ditches, gutters, channel's, <br />roadways and pipes which link the cross-sectional overland flow <br />uni ts and convey the discharge to the drainage outlet. The <br />geometry of the overland flow units is described by flow lengths, <br />flow width and slope. The conveyance system elements are <br />characterized by their slope, lengths, dimensions and shape. The <br />1 "=100' Breckenridge Topographic Mapping (1980) was the maj or <br />source for developing this information. In addition numerous <br />previous drainage reports and plans were reviewed to determine the <br /> <br />20 <br />