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<br />OR~fl <br /> <br />several other options for modeling interception and infiltration, <br />the curve number approach was selected due to the limited available <br />of data for selecting or calibrating the parameters required for <br />the other methods. Kinematic wave routing was used to simulate <br />overland and channel flow. Kinematic wave routing was considered <br />appropriate because slopes in the basin are quite steep. For this <br />condition, the parameters describing the kinematic wave <br />approximation are readily obtained from the available data. The <br />other methods available for overland flow routing required <br />empirically derived data and calibration to produce reasonable <br />results. <br /> <br />Data <br /> <br />The main data requirements for the model include: watershed, <br />geometry, flow resistance, rainfall, and rainfall loss parameters. <br />Descriptions of the parameter used and the sources from which they <br />were derived are presented in the following paragraphs. <br /> <br />Watershed Geometry <br /> <br />Watershed geometry includes the delineation of the watershed into <br />a network of overland flow units and channels, areas associated <br />with each overland unit, lengths and slopes of overland and channel <br />units, and the size and shapes of channels. Except for the latter <br />category, all the watershed geometric information was derived from <br />7.5 minutes USGS topographic maps. The channel geometry and shape <br />were developed from field inspections. All channels were modeled <br />as trapezordal or triangular. <br /> <br />Field Resistance <br /> <br />Flow resistance for channel flow is cahracterized by Manning'S n. <br />For the majority of channels in the simulation, n was varied <br />between 0.05 and 0.06. The overland flow resistance is described <br />by an overland flow roughness factor N. This parameter was varied <br />between values of 0.25 to 0.30. <br /> <br />Rainfall <br /> <br />Two parameters are required for rainfall, the total storm volume <br />and a hyetoqraph which distributes the rainfall over the storm <br />period in various intensities. Rainfall volumes were derived from <br />NOAA (1973). Two separate sets of rainfall volumes were utilized. <br />One to represent the rainfall in the mountains above the valley <br />floor and another to represent the rainfall in the lower elevations <br />of the valley floor. The 24-hour rainfall volumes for each are <br />listed below. <br /> <br />11 <br />