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<br />FIGURE 4
<br />Study Reach with HvdrolOQic Points
<br />11o,;nBnundaf)'
<br />Co>untyLine
<br />City G"l(< [:},
<br />SCAI.E, One inch "'IUal> "ppr<,~imat.ly 16 miles
<br />
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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 Eltistin~ Oa!ll
<br />
<br />For locations wherc existing detailed hydrologic anaiyses were availab1c,thos e arIalyseswere used
<br />to obtain peak 50-year and 10o-year flows. For other locations, statistical analyses of:.1ream
<br />gages and existing regional hydrologic anal>'scs were examined. As is explained in the next
<br />paragraph,thoseana1yses were found to be inconsislent with the existing adopted anaIy sesand
<br />were not used for this report.
<br />
<br />
<br />A draft floodplain study being jointly prepared by the U.S. Anny Corps of Engineers and the
<br />CWCB and 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 OeBeque Canyon. FEMA flo'WS were available
<br />for the Colorado River from Palisade, Culorado downstream to Froita. The USGS performed
<br />frequency analyses on gage locations near DeBeque, near Cameo and near the staleline. The
<br />USGS gage analysis values were lower than the Corps values by 7 to 10 percent. In order 10
<br />maintain consistency, the CotpSvalues wercselected for this study.
<br />
<br />3.2 New Hvdrolollic Information
<br />
<br />The remaining hydrologic points can be divided into two groups: Group I) Three hydrologic
<br />points were localed within reaches tbat 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 />reaches downstream of the SalO Hydrology Report, so they had not previously been analyzed.
<br />Hydrologic analyses of the 50-year and l00-year flood flows for the hydrologic points in Group
<br />1 were performed through interpolation of known flow values. Since (,[etaile(,[ information already
<br />existed, the flo'WS werc not used to compute fl",(",d depths and no changes wcre made to the
<br />detailed floodplain maps, (The flow va.lu~ are provided in this report simply for informalion
<br />purposes,)
<br />
<br />Thc known values for points near the Group I poinls wcre enlered into a curve fitting computer
<br />program which selects an equation that provides a c10se descriptionofthc plo lledcurvc. Flow
<br />values for the three Group I locations on the Colorado River (rivcr milcs 80-75, 42-45 and 25-
<br />28) wcrc calculated. 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 compuled the flows at these locations by using thc 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 />whcre:
<br />
<br />Q"'k*A'
<br />Q=50-yearor 100-ycarflow;
<br />A=drainagearea;
<br />k"'uconstant; and
<br />c"'anexponenl
<br />
<br />10
<br />
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