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<br />average of hydrologic soil type (UDFCD, 1969). The weighted average of hydrologic soil
<br />type for each subwatershed was computed based on superimposing the hydrologic soils
<br />maps (Appendix A) onto the subwatershed maps,
<br />
<br />3.7.4 Routing Connectivity
<br />
<br />3.7 UDSWM2 Modeling
<br />
<br />The routing connectivity of the conveyance elements, design points, and subwatershed
<br />hydrographs was incorporated into the UDSWM2 models according to the connectivity
<br />diagrams provided in Appendix 1.
<br />
<br />A UDSWM2 model was created for each watershed (total of 6) to route the CUHP gener-
<br />ated hydro graphs through the existing stream network. Conveyance element parameters
<br />required for the UDSWM2 model include the conveyance element identifier, channel
<br />bottom width, length, invert slope, side slopes, hydraulic roughness, and routing
<br />connectivity, A summary of these characteristics is shown in Appendix I and the methods
<br />for estimating these characteristics is described in the following sections.
<br />
<br />3.8 Results
<br />
<br />3.8.1 Baseline Peak Flows, Hydrographs,
<br />and Runoff Volumes
<br />
<br />3.7.1 Conveyance Element Identification Number
<br />
<br />The baseline peak: discharges for the 2-, 5-, 10-, 50-, 100-, and 500-year events for future
<br />development conditions are summarized in Appendix K. Plots of the peak: discharges
<br />"p.~n~ ~fTp.<;aTn cto;ahnn <::lIrp. nrr",.ir1""rl 1n Ann....nniv T Tn ';IAA-it1n.n hur1r/"\nT-::anhco fnr <;all c'tn1""l"t'1c
<br />,--~-- ----&. -~--_&- -- r-- . ---- ~& & -rr--&~& -. ~& -----_&, UJ ---0""-.1"--- --- -..... ......_...-~...
<br />are provided at selected locations in Appendix M, The information shown in Appendices
<br />K through M was organized so that it only includes hydrologic results pertaining to the
<br />appropriate area adjustment shown in Table 3-3,
<br />
<br />Conveyance elements were numbered from downstream to upstream for each stream as
<br />shown in Appendix F. All conveyance elements were identified with even numbers,
<br />Design points were located at the upstream and downstream ends of each conveyance
<br />element number and identified by the appropriate odd numbers,
<br />
<br />All streams were modelled as trapezoidal cross sections, Bottom widths, lengths, invert
<br />slopes, and side slopes were estimated from the 1:24,000 USGS quadrangle maps, In
<br />some cases, streams were represented by a base flow channel and an overflow floodplain
<br />channel.
<br />
<br />Hydrologic results for the watershed upstream of the study area were not included in
<br />Appendices K through M, This is because the upstream model was designed for the
<br />specific purpose of generating inflow hydrographs to the study area, To provide
<br />representative discharges at specific design points within the upstream watershed, addi-
<br />tional subwatersheds may need to be defined and different area adjustments may need to
<br />be analyzed,
<br />
<br />3.7.2 Stream Geometry
<br />
<br />n = 0.393 x (S)0.38 x (R)'o,16
<br />
<br />(1)
<br />
<br /> Table 3-5
<br /> 100- Year Peak Discharges at Selected Locations
<br /> l00-Year Peak Discharges (cfs)
<br /> Existing Development Future Development
<br /> Location Conditions Conditions
<br /> Coyote Run
<br />1-70IU,S. 36 6,940 11,600
<br />Immediately Upstream of Box Elder Creek Confluence 8,600 14,400
<br /> Box Elder Creek
<br />Upstream Study Limit 8,880 10,800
<br />1-70 8,820 11,800
<br />Immediately Upstream of Coyote Run 8,760 11,700
<br />Immediately Downstream of Coyote Run (Downstream 9,090 14,900
<br />Study Limit)
<br />
<br />3.7.3 Roughness
<br />
<br />The roughness or Manning's "n" value for each conveyance element was detennined using
<br />Equation 2 from the UDSWM2 Users Manual (UDFCD, 1985b), which is shown below,
<br />
<br />where:
<br />
<br />n = Manning's roughness coefficient
<br />S = friction slope (feet/feet)
<br />R = hydraulic radius (feet)
<br />
<br />This equation is the result of research work by Robert D, Jarrett of the USGS (Jarrett,
<br />1984) and is recommended for hydrologic routing in natural channels, For this study, the
<br />friction slope was approximated using the invert slope and the hydraulic radius was
<br />approximated for lOO-year flood conditions, The Manning's "n" value for the conveyance
<br />elements generally ranged from 0,03 to 0,06,
<br />
<br />One-hundred year peak: discharges at selected locations along Coyote Run and Box Elder
<br />Creek are shown in Table 3-5, Runoff volumes at selected locations along Coyote Run
<br />and Box Elder Creek are shown in Table 3-6.
<br />
<br />3-4
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<br />DENlOO17681.WP5
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