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 2of4

recommendations made by the USFWS for the Recovery Program to date have employed methods to .
carefully study the flow - habitat relationship on the river in question. The results of CD OW's study
prove the importance of using habitat and flow information to make scientifically sound, biologically
based flow recommendations.

The study focused on native fish that are not yet listed as endangered. The bluehead sucker,
flannelmouth sucker, and to a lesser extent the roundtail chub were the primary fishes considered in
this study. The four endangered fish species were not specifically targeted in this study, but many of
the results apply to them also. The use of the more abundant native species provided more accurate
population estimates and also information on flows necessary to maintain healthy populations of
these species to prevent future listing under the Endangered Species Act.

Anderson selected three study sites on the Yampa River and two sites on the Colorado River. The
Sevens, Duffy, and Lily Park sites on the Yampa River are located between the Little Yampa
Canyon and the confluence with the Little Snake River. The Clifton and Com Lake sites are both
located in the 15-Mile Reach of the Colorado River. Data was collected for several years at each
site. The channel topography of these sites was mapped and a 2-D flow model was used to create
flow simulations. The location and amount of meso-habitat types such as rapids, riffles, runs and
pools were identified for various flows. Electrofishing at various flows provided population
estimates, size and biomass data. A careful comparison of the fish population versus the habitat
availability for different flows was used to create flow-habitat suitability curves for the native
bluehead and flannelmouth sucker for each study site.

These curves provide the entire range of results rather than one number for a flow recommendation.
Anderson used the curves to determine the minimum instream flow recommendation. Rather than
make additional recommendations for wetter years, as is done in the Recovery Program, the curves
created by Anderson could be used for water management in every year. Using the water
availability for the year and the flow-habitat curves, one can identify the most desirable flow regime
under the circumstances.

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Results
Anderson's study found an extremely strong relationship between summer and fall base flows and
habitat availability and fish population. While spring peaks are known to be an important trigger in
the spawning process ofthe endangered fish species, the exact relationship between peak flows and
fish abundance is not clear. This suggests that the Recovery Program needs to continue to balance
its desire for spring peak flows with maintenance of minimum base flows to support fish
populations.

Successive years of low base flows have stronger negative impacts on native fishes than occasional
short periods of low base flow, as the situation on the Yampa during these past few dry years
indicates. Anderson is performing additional work in the study areas to further try and understand
the impacts of the low flows of2000 - 2002 on the fish populations.

The channel morphology ofthe Colorado and Yampa rivers is very similar. The flow-habitat curves .
are therefore very similar as well and suggest that, given similar flow regimes, the two rivers would
provide similar amounts of habitat and support similar fish populations. However, flows during the
Flood Protection. Water Project Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation Planning