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Red Mesa Ward Site Hydrology <br /> 2. Length of Watercourse (L). Watercourses were digitized onto the United States Geological <br /> Survey (USGS) quadrangle maps. Watercourse lengths were queried electronically using <br /> Geographic Information System(GIS). Watercourses are shown in light blue on Figure 1. <br /> 3. Basin Slope (S). Basin slopes were determined by taking the total relief in feet (determined <br /> from appropriate USGS 1:24,000 quadrangle maps) and dividing by the length of the <br /> watercourse in miles. <br /> 4. Distance to Centroid (Lca). Subbasin centroids were determined digitally using AutoCAD. <br /> The distance to the centroid is the length along the watercourse from the design point to a <br /> point opposite the centroid on the watercourse, as shown on Figure 1. <br /> 5. Average Weighted Manning's n (Kn). The average weighted (by stream length) Manning's n <br /> for the principal watercourses in the drainage basin. <br /> 6. Lag Time (Lg). The lag time is calculated as follows: <br /> Lg=26 * Kn * ((Lca * L)/S")"3 <br /> 7. Unit Duration (D). The unit rainfall duration is approximated by the lag time divided by 5.5. <br /> This will yield adequate definition near the peak of the hydrograph. <br /> 8. Lag Time Plus Semiduration (Lg + D/2). The calculated hydrograph is expressed in percent <br /> of the lag time plus the semiduration, which is calculated as the lag time plus half the unit <br /> duration. <br /> 9. Basin Factor. The basin factor is calculated as follows: <br /> BF =L * Lca/S" <br /> 10. Unit Runoff Volume (V). Volume of runoff generated by one inch of excess precipitation <br /> expressed in one-day cubic feet per second. <br /> 11. Discharge for subbasin (Qs). The discharge for the subbasin is calculated as follows: <br /> 991-077.070 Wright Water Engineers, Inc. Page 3 <br /> September 2002 <br />