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<br />I <br /> <br />I <br /> <br />CUHPlUDSWM2 <br />Future <br />(cfs) <br /> <br />Existing <br />(cfs) <br /> <br />tOO-Year Peak Flow Summary <br /> <br />USGS <br />(cfs) <br /> <br />CWCB <br />(cfs) <br /> <br />FEMA <br />(cfs) <br /> <br />FIS <br />( cfs ) <br /> <br />Table 5 <br /> <br />Basin <br />Area <br />(SM) <br /> <br />Location <br /> <br />and aerial <br /> <br />represented by <br /> <br />field observations <br /> <br />subbasin designations and routing elements, is <br />Hydrology Model Routing Flow Diagram. <br /> <br />mappmg, <br /> <br />topographic <br /> <br />data, <br /> <br />measurements from USGS DEM <br /> <br />CUHP <br />(Wolf Creek), <br /> <br />UDSWM2 model, including the <br />(Comanche Creek) and 2b <br /> <br />were based on <br />photographs. <br /> <br />The <br />Figures 2a <br /> <br />I <br /> <br />Wolf Creek at <br />Arapahoe County Line <br /> <br />I <br /> <br />12,917 <br /> <br />12,427 <br /> <br />10,366 <br /> <br />11.137 <br /> <br />12,904 <br /> <br />12,408 <br /> <br />10,366 <br /> <br />11.125 <br /> <br />140 <br /> <br />9.800 <br /> <br />9,150 <br /> <br />9,580 <br /> <br />9 <br /> <br />12.810 <br /> <br />14,420 <br /> <br />12,840 <br /> <br />13.860 <br /> <br />12,570 <br /> <br />12.320 <br /> <br />11 ,210 <br /> <br />12,000 <br /> <br />18,570 <br /> <br />20,200 <br /> <br />83.7 <br /> <br />100.3 <br /> <br />94.4 <br /> <br />84.0 <br /> <br />Wolf Creek above <br />Confluence wi <br />Comanche Creek <br /> <br />Comanche Creek at <br />Arapahoe County Line <br /> <br />Comanche Creek below <br />Confluence wi <br />Little Comanche Creek <br /> <br />Kiowa Creek <br /> <br />Based on USGS maps the confluence of Comanche Creek with Kiowa Creek appears to occur downstream of <br />the study limit. However, after receiving more accurate and detailed topographic data for the study area it was <br />determined that flood flows in Kiowa Creek would leave its poorly defined low flow channel much sooner and <br />merge with flows in Comanche Creek approximately three miles upstream of the confluence of the low flow <br />channels. Therefore, an estimate of the 100-year flow in Kiowa Creek was required to complete the <br />delineation of the floodplain at the northerly end of the Study Area. An estimate for the combined flow of <br />Kiowa and Comanche Creeks was made by applying the value of 94.48 cfs/SM (23,166 cfs/245.2 SM), <br />developed for Comanche Creek, to the combined basin area of the two creeks of 517.2 square miles. <br />Therefore, a 100-year flow of 48,865 cfs was used for the lower reach of Comanche Creek as it combines with <br />Kiowa Creek. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />12,061 <br /> <br />23,245 <br /> <br />12,049 <br /> <br />187 <br /> <br />23 <br /> <br />10,640 <br /> <br />13,400 <br /> <br />16,560 <br /> <br />24,400 <br /> <br />12,920 <br /> <br />17,490 <br /> <br />124.0 <br /> <br />224.3 <br /> <br />Comanche Creek above <br />Confluence wi <br />Wolf Creek <br /> <br />Comanche Creek below <br />Confluence wi <br />Wolf Creek <br /> <br />Hydrology Results <br /> <br />Calculations for the regression equation estimates and input and output files for the CHUP-UDSWM2 models <br />are provided in the Appendix. The computer model files have also been provided on a CD. A summary of <br />100-year peak flows used in the PISs and determined by these methods, at key study locations, is provided in <br />the Table 5, 100-Year Peak Flow Summary. These results are also shown graphically on Figure 3, 100-Year <br />Peak Flow Comparison. Storm hydrographs for key locations on Comanche and Wolf Creeks are shown on <br />Figure 4, 100- Yr Hydrographs. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />23,245 <br /> <br />the CUHP- <br /> <br />166 <br /> <br />Comanche Creek using <br /> <br />23 <br /> <br />13.870 <br /> <br />25,870 <br /> <br />the detailed study area on <br />in Table 6 below <br /> <br />16,780 <br /> <br />245.2 <br /> <br />Additional flows were estimated for use in <br />UDSWM2 computer model. These flows are shown <br /> <br />Comanche Creek at <br />Weld County Line <br /> <br />These results show that the original PIS flows are, at least, 40% higher than flows estimated by other methods. <br />The regional method developed by Thomas and promoted by FEMA agrees better with the other methods for <br />smaller basin areas and provides consistently lower estimates of flow as the basin size increases. The <br />regression equation developed by the CWCB agrees fairly closely with the CUHP-UDSWM2 model, but <br />consistently provides a somewhat higher estimate of flow. The USGS equation provides the lowest estimate of <br />flood flows. Flows estimated by the USGS equation are between 11 and 29 percent lower than the next highest <br />estimate. <br /> <br />I <br /> <br />I <br /> <br />Model <br /> <br />500-year <br />16,939 <br /> <br />18,200 <br /> <br />Estimated Flow (cfs) <br />50-Year tOO-year <br />4,445 10,370 <br /> <br />Comanche Creek Flood Flows for Detailed Hydraulic <br /> <br />11.137 <br /> <br />4.773 <br /> <br />to- Year <br />1,030 <br /> <br />1.103 <br /> <br />Location <br /> <br />Table 6 <br /> <br />the watersheds will not appreciably increase <br />can. also. be considered to effectively <br /> <br />so show that proposed future development within <br />Therefore, the floodplain delineated for existing conditions <br />a future condition floodplain <br /> <br />These results al <br />flood flows. <br />represent <br /> <br />I <br /> <br />I <br /> <br />Comanche Creek at Arapahoe- <br />Adams County Line <br /> <br />26th A venue <br />Detailed Study) <br /> <br />Comanche Creek at <br />(Northern Limit of <br /> <br />the <br /> <br />were considered reasonable for <br /> <br />model flows <br /> <br />Based on these results, the CUHP-UDSWM2 computer <br />determination of floodplain limits within the Study Area. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />McLaughlin Water Engineers <br />P:\2000\AO-029\OO300\Final Floodplain Report\Final Report.doc <br /> <br />5 <br /> <br />Comanche Creek and Wolf Creek <br />Floodplain Study. May 2002 <br /> <br />I <br />