WSP10633

• File Number: 8240.200.30.E
• Description: Guru I And II
• Basin: Colorado Mainstem
• Date: 1/1/1993
• Author: Jack Stafford
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin: Review and Synthesis of Ecological Information, Issues, Methods and Rationale
• Water Supply Pro - Doc Type: Publication

The apparent importance of variable, but clearly seasonal, flow regimes and associated

biophysical interactions were used as key rationale for the flow recommendations made by the U.S.

Fish and Wildlife Service. For the Yampa, Green and Colorado Rivers, flows were recommended

that would increase amplitude of the spring peak and reduce short-term fluctuations from

hydropower operations at baseflows. However, on the Green River, the peak flows recommended

for wet years were considerably less than flows of record and allowed substantial flow fluctuations

during the late summer, fall and winter (baseflow) period on all years. Moreover, a complex flow-

habitat model was used to support flow recommendations on the Colorado River, but model output

was discarded on the Green and Yampa Rivers. Review herein of models currently used to

mechanistically detennine an incremental relationship between flow and river conditions favorable

to the endangered fishes revealed that none, including the one used on the Colorado River, were

sufficiently well developed to be used exclusive of many other ecological measures.

Inconsistencies in rationale and perceived need for a predictive model compromised the science that

strongly supported rereguIation of flows in the Green and Colorado Rivers to produce more natural,

seasonal pattems.

Based on review of the ecological infoffiIation and recognizing the problems in the

methodological approaches that were used to derive flow recommendations, several key

uncertainties appear to be critical to the goal of establishing flow regimes that will ultimately recover

the endangered fishes.

. Flow seasonality and its correlates (e.g., temperature and physical habitat) may not be the

factor(s) limiting recovery of the native fishes.

. Given the high societal value placed on taiIwater trout fisheries, and the high priority

placed on meeting entitlements under the ColoradO compact and current water law (i.e., the "law of

the river"), water volume in the Colorado and Green Rivers may be insufficient to produce flows

required to recover the fishes.

ii

GI 0011