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u01592 STATE OF COLORADO OFFICE OF THE.EXECU"IIVEJlIRECTOR " ~ · Kppenalx r of {fie l'znaI ~upplement to the Fmal Envlronmental Statement for the ~ ~ i. 1..-" Departme.9lfif~i1r~SPfMa Project (March, 1996) identified the need for an 8 cfs fish mainte 1313 SherE;1~:n'Stceet,-'RooV11'i8 . . . Denver, cmHiMJfu~:ij~ La Plata River below Long Hollow Creek. A 15-cfs fish mIgratIOn flow Phone: (3lWdUitd31M,;, maintained for 2 weeks in the spring and fall. Support for these ;~~;3~~)~~:~~endations is found in Attachment X: Internal Technical Discussion-SouthWA.T'lfRAL Ute Diversion Dam Background/Position Statement (1995): "Eight cfs is the absol~SOURCES minimum (base flow). This flow was measured through the most densely inhabited portion of the La Plata River by roundtails during lowest flow conditions encounterM1 ~s -~vernor summer." Richard Valdez of Bio/West, Inc. identified a fish maintenance flow of 8 ~~II George for 47 weeks of the year (excluding spring runoff) for the La Plata River below Longxecutive Director Hollow in "Animas La-Plata Project, La Plata River Native Fishes General Mitigation And Monitoring Recommendations" (September, 1995). ( ~ 'J . The Animas-La Plata Project Conceptual Mitigation and Monitoring Plan (April, 1996) prepared for the Bureau of Rec1amation by BiolWest, Inc. identified a minimum channel maintenance flow of 85 cfs in the La Plata River below Long Hollow for one week per year, preferably in the spring. From 1989 to 2002, La Plata River flows measured at the USGS gage in Hesperus never fell below 4 cfs (Biological Assessment for Proposed Long Hollow Reservoir, September, 2003, Wright Water Engineers, Inc. and Ecosphere Environmental Services). This suggests a 4-cfs flow might serve as a reasonable winter base flow for the lower La Plata River. . In 1995, the CDOW and BOR collected instream flow cross section data at four sites on the La Plata River. Two of the sites were upstream of Long Hollow and two were downstream. The measured flows ranged from 4.7 cfs to 12.5 cfs. We processed this field data using the R2CROSS model and generated flow recommendations using the standard hydraulic criteria (average depth, average velocity, and percent of bank full wetted perimeter). Two hydraulic criteria are met at flows ranging from 4 cfs to 9 cfs; all three criteria are met at flows ranging from 10 cfs to 24.5 cfs. Using the currently accepted technique (used by the CDOW and BLM when recommending flows to the CWCB) for analyzing multiple transects, the average of the in-range flows is 7.3 cfs for the winter, base flow period and 15.4 cfs for tne summer higher flow period. CDOW flow recommendations seem to be very much in line with the flow recommendations suggested by others (see above text). In light ofthe 1989 - 2002 hydrologic data, it seems reasonable to expect that 4 cfs is always in the stream. Thereforel CDOW suggests that the applicant analyze and model reservoir operations using 4 cfs as a target flow for the blL..~__ e:r1'fire winter base flow period for the entire reach of the La Plata River from Long ~ IIOffow to the state line. . Since 4 cfs is a substantial departure from the flow recommendations submitted by others, we consulted Miller's 1995 report. In this report, Miller analyzed the hydraulic behavior of several pools, runs, and riffles. This analysis suggests only slight changes in stream channel hydraulics (average depth, maximum depth, average velocity, and wetted perimeter) in riffles betWeen 7 cfs and 4 cfs. Therefore, CD OW is of the opinion that 4 Board of Land Commissioners. Division of Minerals & Geology/Geological Survey Oil & Gas Conservation Commission. Colorado State Parks. DiviJon of Forestry Water Conservation Board. Division of Water Resources. Division of Wildlife