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<br />001586 <br /> <br />flow in the La Plata River below Long Hollow Creek. A 15-cfs fish migration flow <br />would be maintained for 2 weeks in the spring and fall. Support for these <br />recomrnendations is found in Attachment X: Internal Technical Discussion-Southern <br />Ute Diversion Dam Background/Position Statement (1995): "Eight cfs is the absolute <br />minimum (base flow). This flow was measured through the most densely inhabited <br />portion of the La Plata River by roundtails during lowest flow conditions encountered last <br />summer." Richard Valdez ofBio/West, Inc. identified a fish maintenance flow of8 cfs <br />for 47 weeks of the year (excluding spring runoff) for the La Plata River below Long <br />Hollow in "Animas La-Plata Project, La Plata River Native Fishes General Mitigation <br />And Monitoring Recommendations" (September, 1995). <br /> <br />· The Animas-La Plata Project Conceptual Mitigation and Monitoring Plan (April, 1996) <br />prepared for the Bureau of Reclamation by Bio/West, Inc. identified a minimum channel <br />maintenance flow of 85 cfs in the La Plata River below Long Hollow for one week per <br />year, preferably in the spring. <br /> <br />· From 1989 to 2002, La Plata River flows measured at the USGS g~~S never <br />fell below 4 cfs (Biological Assessment for Proposed Long Hollow Reservoir, Septernber, <br />2003, Wright Water Engineers, Inc. and Ecosphere Environmental Services). This <br />suggests a 4-cfs flow might serve as a reasonable winter base flow for the lower La Plata <br />River. <br /> <br />· In 1995, the CDOW and BOR collected instream flow cross section data at four sites on <br />the La Plata River. Two ofthe sites were upstream of Long Hollow and two were <br />downstream. The measured flows ranged from 12.5 cfs to 4.7 cfs. We processed this <br />field data using the R2CROSS model and generated flow recommendations using the <br />standard hydraulic criteria (average depth, average velocity, and percent of bank full <br />wetted perimeter). Two hydraulic criteria are met at flows ranging from 4 cfs to 9 cfs; all <br />three criteria are met at flows ranging from 10 cfs to 24.5 cfs. Using the currently <br />accepted technique (used by the CD OW and BLM when recommending flows to the <br />CWCB) for analyzing multiple transects, the average of the in-range flows is 7.3 cfs for <br />the winter, base flow period and 15.4 cfs for the summer higher flow period. CDOW <br />flow recommendations seem to be very rnuch in line with the flow recommendations <br />suggested by others (see above text). In light of the 1989 - 2002 hydrologic data, it seems <br />reasonable to expect that 4 cfs is always in the stream. Therefore, CDOW suggests that <br />the applicant analyze and model reservoir operations using 4 cfs as a target flow for the <br />entire winter base flow period for the La Plata River from Long Hollow to the state line. <br /> <br />· Miller's 1995 report suggests only slight changes in stream channel hydraulics (average <br />depth, maximum depth, average velocity, and wetted perimeter) in riffles between 7 cfs <br />and 4 cfs. Therefore, at a minimum 4 cfs is needed to protect the native fishery in the La <br />Plata River downstream of Long Hollow during the winter base flow months. <br /> <br />· It has been suggested that the current stream channel geometry is not indicative of what <br />would exist if the Long Hollow Reservoir proj ect proceeds. The proposed mitigation <br />includes some channel restoration which may significantly change the stream channel <br /> <br />3 <br />