<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 />
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<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 />
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<br />
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