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DENlOO15186.WP5 3-4 The routing connectivity of the conveyance elements, design points, and subwatershed hydrographs was incorporated into the UDSWM2 models according to the connectivity diagrams provided in Appendix J. 3.7.4 This equation is the result of research work by Robert D. Jarrett of the USGS (Jarrett. 1984) and is recommended for hydrologic routing in natural channels. For this study, the friction slope was approximated using the invert slope and the hydraulic radius was approximated for loo-year flood conditions. The Manning's "n" value for the conveyance elements generally ranged from 0.03 to 0.06. where: The roughness or Manning's "n" value for each conveyance element was determined using Equation 2 from the UDSWM2 Users Manual (UDFCD, 1985b), which is shown below. Routing Connectivity n = Manning's roughness coefficient S = friction slope (feet/feet) R = hydraulic radius (feet) n = 0.393 x (S)O.38 x (R)-o.16 (1) Table 3-5 100- Year Peak Discharges at Selected Locations 100- Y ear Peak Discharges (cfs) Existing Future Development Development Location Conditions Conditions Coyote Run I-70/U.S. 36 6,950 11 ,600 Immediately Upstream of Box Elder Creek 8,630 14,400 Confluence Box Elder Creek Upstream Study Limit 8,960 11,200 1-70 8,900 12,000 Immediately Upstream of Coyote Run 8,840 11,900 Immediately Downstream of Coyote Run 9,140 15,200 (Downstream Study Limit) I I II I I 'I I 3.7.3 Roughness One-hundred year peak discharges at selected locations along Coyote Run and Box Elder Creek are shown in Table 3-5. Runoff volumes at selected locations along Coyote Run and Box Elder Creek are shown in Table 3-6. All streams were modelled as trapezoidal cross sections. Bottom widths, lengths, invert slopes, and side slopes were estimated from the 1 :24,000 USGS quadrangle maps. In some cases, streams were represented by a base flow channel and an overflow floodplain channel. 3.7.2 Stream Geometry Conveyance elements were numbered from downstream to upstream for each stream as shown in Appendix F. All conveyance elements were identified with even numbers. Design points were located at the upstream and downstream ends of each conveyance element number and identified by the appropriate odd numbers. 3.7.1 A UDSWM2 model was created for each watershed (total of 6) to route the COOP gener- ated hydrographs through the existing stream network. Conveyance element parameters required for the UDSWM2 model include the conveyance element identifier, channel bottom width, length, invert slope, side slopes, hydraulic roughness, and routing connectivity. A summary of these characteristics is shown in Appendix 1 and the methods for estimating these characteristics is described in the following sections. Conveyance Element Identification Number The baseline peak discharges for the 2-, 5-, 10-, 50-, 100-, and 500-year events for existing and future development conditions are summarized in Appendix K. Plots of the peak discharges versus stream station are provided in Appendix L. In addition, hydrographs for all storms are provided at selected locations in Appendix M. The information shown in Appendices K through M was organized so that it only includes hydrologic results pertaining to the appropriate area adjustment shown in Table 3-3. I I I I .1 I I I I I Hydrologic results for the watershed upstream of the study area were not included in Appendices K through M. This is because the upstream model was designed for the specific purpose of generating inflow hydrographs to the study area. To provide representative discharges at specific design points within the upstream watershed, addi- tional sub watersheds may need to be defined and different area adjustments may need to be analyzed. 3.8.1 Baseline Peak Flows, and Runoff Volumes Hydrographs, 3.7 UDSWM2 Modelling 3.8 Results I I