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<br />FIGURE 4
<br />Study Reach with HvdrolOQic Points
<br />lIa,;nBounda,,'
<br />Co>untyLine
<br />City G"l(< [:},
<br />SCAI.E, One inch "'IUa!> Iippr<,~imat.ly 16 miles
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<br />
<br />COLORADO RIVER BASIN
<br />COLORADO WATER CONSERVATION BOARD 3/1/5
<br />
<br />,
<br />-'-
<br />
<br />3.0
<br />
<br />HYDROLOGIC ANALYSIS
<br />
<br />
<br />3.1 E"istin~ Data
<br />
<br />Forlocalions wherc existing detailed bydrologic analyses were availab1c,thos e analyses were used
<br />to obtain peak 50-year and lOo-year flows. For other locations, statistical analyses of:.1ream
<br />gages and existing regional hydrologic anaI>'ses were examined. As is explained in the next
<br />paragraph,thoseanalyses were found to be inconsistent with the existing adopted anaIy sesand
<br />were not used for tllls report.
<br />
<br />
<br />A draft floodplain study being jointly prepared by the U.S. Army Corps of Engineers and the
<br />CWCB WId published FEMII. studies provided 50-year and lOO-year flows for much of the study
<br />reach. Corps of Engineers flows were available for the Colorado River from Rifle, Colorado, at
<br />the upstream limit of this study, downstream to DeBeque Canyon. FEMII. flows were available
<br />for the Colorado River from Palisade, Colorado downstream to Froita. The USGS performed
<br />frequency analyses on gage locations near DeBeque, near Cameo and near the stateline, The
<br />USGS gage analysis values were lower than the Corps values by 7 to 10 percent. In order to
<br />maintain consistency, the Corps values were selected for this srudy.
<br />
<br />3.2 New Hvdrolollic Information
<br />
<br />Th~ remaining hydrologic points can be divided into two groups: Group I) Three hydrologic
<br />points were located within reaches that had already been studied by detailed methods, b utthere
<br />weren't any published flow values for those specific points; Group 2) Two points were in
<br />r~aches downstream of the SalO Hydrology Report, so th~y had not previously been analyzed.
<br />Hydrologic analyses of the 50-year and lOO-year flood flows for the hydrologic points in Group
<br />1 were performed through interpolation of known flow values. Since d~tailed informatioll already
<br />existed, the flows were not used to compute lk......d depths and no changes wcre made to the
<br />detailed floodplain maps. (The flow vaJu~ are provided in this report simply for information
<br />purposes.)
<br />
<br />The known values for points near the Group 1 points were entered into a curve fitting computer
<br />program whieh seleets an equation that provides a c10se description of the plo Itedeurve. Flow
<br />values for the three Group I locations on the Colorado River (river miles 80-75, 42-45 and 25-
<br />28) wcre caleulated. A similar procedurc involving extrapolation instead ofintcrpolation was
<br />us<:d for the hydrologic points in Group 2 (river miles 0-10 and 10-12). The curve fitting
<br />program computed the flows at these locations by using the corresponding drainage areas at each
<br />location. Table j summarizes the data at the selected hydrologic locations. The equation tor the
<br />Colorado River below Rille is:
<br />
<br />where:
<br />
<br />Q"'k*A'
<br />Q=50-yearor IOO.yearflow;
<br />A=dralnagearea;
<br />k"uconstatlt; and
<br />~ .. an exponent
<br />
<br />10
<br />
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