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Section 6
<br />Water Needs Assessment
<br />1995), which incidentally contradict the flow
<br />recommendations developed for the state line.
<br />work and consider using this more data-intensive
<br />methodology for future flow recommendations.
<br />Flow recommendations for the 15-mile reach are
<br />summarized in Table 6-11 on a mean monthly discharge
<br />basis. These recommendations are for the "top of the
<br />15-mile reach." These recommendations take into
<br />account and are for a point immediately below the
<br />Orchard Mesa Power Plant return and Grand Valley
<br />Irrigation Company diversion (USFWS 1995).
<br />Recommendations are provided for years of high, above-
<br />average, below-average, and low runoff.
<br />The flow recommendations are data specific to the
<br />15-mile reach and relate to adult Colorado pikeminnow
<br />habitat preferences, general relationships between stage
<br />and habitat quantity and quality, and discharge
<br />thresholds for sediment transport. As additional studies
<br />are completed, knowledge of the relationship between
<br />discharge and fish habitat will continue to evolve and
<br />recommendations will continue to be refined.
<br />The CDOW, at the request of CWCB, is conducting
<br />research to provide detailed information on the
<br />relationship between discharge, habitat availability, and
<br />fish population. The CDOW intensively studied several
<br />sites on the Yampa and Colorado Rivers to obtain very
<br />specific data about the habitat type and quantity and fish
<br />abundance and biomass found at various discharges.
<br />This more detailed analysis will help decisionmakers
<br />maximize the benefits of available water during any
<br />particular hydrologic condition. The CWCB and CDOW
<br />have requested that the Recovery Program review this
<br />The flow rate is the percent of years that the
<br />recommended flows should be provided based on winter
<br />snow pack levels. For example, in the wettest 25 percent
<br />of years, flows in June should average at least
<br />15,660 cfs; stated another way, this recommendation
<br />should be met in 5 of every 20 years. During low-water
<br />years, June flows should average no less than 6,850 cfs,
<br />and such a minimum should occur at a rate of no more
<br />than 4 in 20 years (20 percent).
<br />Numerous instream flow rights have been decreed on
<br />major rivers and tributaries in the Colorado River Basin
<br />(http://cwcb.state.co.us/isf/Downloads/Index.htm). Some
<br />of the decreed rights on major rivers are listed in
<br />Table 6-12. These rights are year-round rights containing
<br />seasonable variability as reflected in the range of values
<br />as shown. Flow rights on smaller tributaries in the basin
<br />can be found at the above reference.
<br />Instream flows are maintained as requirements or targets
<br />below several BOR projects in the Colorado Basin. A
<br />description of these flows is provided in Table 6-13.
<br />6.3.2.2.2 Water-Based Recreation
<br />Numerous river reaches in Colorado are used for
<br />whitewater rafting. Table 6-14 shows the reaches in the
<br />Colorado basin that are listed for rafting use by American
<br />Whitewater.
<br />Table 6-11 Recommended Mean Monthly Flows for the Top of the 15-Mile Reach in cfs (Osmundson 1995)
<br />
<br />25% :..
<br />25% :m
<br />1,630 1,630
<br />1,630 s$
<br />3,210
<br />10,720
<br />15,660
<br />7,060 .
<br />1,630 :.
<br />1,630 ~
<br />1,630 0
<br />1,630 r-
<br />1,630
<br />25% 50% 1,630 1,630 1,630 2,440 9,380 14,250 5,370 1,630 1,630 1,630 1,630 1,630
<br />30% 80% 1,630 1,630 1,630 2,260 7,710 11,350 3,150 1,240 1,240 1,240 1,630 1,630
<br />20% 100% 1,240 1,240 1,240 1,860 7,260 6,850 1,480 810 810 810 1,240 1,240
<br />r~
<br />S:\REPORIIWORD PROCESSING\REPORllS6 11-8-04.DOC 6-37
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