BOARD01175

• Board Meeting Date: 1/27/2004
• Description: WSP Section - Riverine Fish Flow Investigations, CDOW Instream Flow Recommendations for Colorado and Yampa Rivers
• Board Meetings - Doc Type: Memo

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Agenda Item 14
January 27-28, 2004 Board Meeting
Page 3 of4

irrigation season in the Yampa River are considerably less than those of the Colorado River.
Therefore, flow recommendations on the Yampa River focus on prevention of habitat degradation
while flow recommendations on the Colorado can focus on maximizing habitat availability and
diversity.

Flows of900 to 1000 cfs in the 15-Mile Reach, as observed during 2000 and 2001, are considered
optimal. Anderson's flow-habitat curves suggest that flows above 1200 cfs do not provide
additional habitat or habitat diversity for the native fish. The USFWS flow recommendations for the
15-Mile Reach call for average monthly flows of 810 cfs in dry years, 1240 cfs in average years and
1630 cfs in wet years.

CDOW Flow Recommendations
Colorado
Flows in the 15-Mile Reach rarely fall below the suitable to optimal range of800 - 1000 cfs. Since
the USGS gage was installed in 1990, summer flows in the 15-Mile Reach were consistently below
800 cfs only in the severe drought of2002. Therefore, it is expected that the 15-Mile Reach will
continue to sustain a healthy population of native fish. DOW has not made a formal flow
recommendation for the 15-Mile Reach at this time. Anderson's work suggests that a flow of 600
cfs is required to maintain 80% of the existing native fish biomass and flows of 900 cfs should
maintain 100% of existing native fish biomass.

Yampa
200 cfs is the recommended instream flow for the Yampa River. This is higher than the USFWS
recommendation of93 cfs.

On the Yampa, low base flows exacerbate the existing problems with an abundance of nonnative
fishes that prey on native fishes or compete with them for existing food and habitat. Yampa
nonnative fish management plus flow management must proceed together to be successful.

Conclusion
Using channel morphology, habitat, fish population and flow data together provides a valid,
biologically-based set of flow recommendations. This method is more labor intensive than the
current methods employed by the USFWS but provides more comprehensive information and should
be more useful in achieving the ultimate goal of sustaining adequate populations of native fish.

The flow-habitat curves created in Rick Anderson's study are a very useful tool for optimizing the
flow regime for any given hydrologic condition. One can study the range of attainable flows and
select a flow target that provides the most benefit for the fish with the water available at the time.

Flood Protection. Water Project Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation Planning