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\. . . , ~ " 15 '. \. t,-, The final irrigation diversion on the upper Colorado River that currently contributes to seasonal flow fluctuations in known occupied squawfish ~abitat is the Grand River Water Users Diversion (otherwise known as Government. . Highline Diversion) located about 8 miles upstream from Palisade, Colorado (RM 193.6) and immediately above the confluence with Plateau Creek. This diversion removes up to 1,600 cfs from the Colorado River during the growing season (April - October), and 800 cfs the remainder of the year. Approximately 625 cfs of the diverted flow during the growing season and the 800 cfs diverted during the remainder of the year are used to produce power and are returned to the Colorado River near Palisade (RM 185). The potential exists for the Colorado River to be nearly dewatered below the Grand Valley Irrigation Company diversion by the combined effects of these major diversions. During times of low flow during the growing season, the diversions are cooperatively operated to maximize the use of available water. Under this cooperative arrangement, water diverted by the Government Highline Diversion is returned, ~r "checked back" to the Colorado River upstream of the Grand Valley Irrigation Company diversion. The "checked back" water is subsequently diverted from the river at RM 185 by the latter, more senior water right holder. The contribution of Plateau Creek and miscellaneous seepage/return flows help maintain minimum flow conditions in the reach upstream from the Grand Valley Irrigation Company facility; however, near dry conditions have occurred in the Colorado River downstream from the Grand Valley Irrigation Company diversion during low-water years. Nearly dewatered conditions occur when flows immediately above the Grand Valley Irrigation Company diversion, including the "checked back" water of the Government Highline System, are approximately the same as or less than the Grand Valley Irrigation Company's water right of 640 cfs. Most of the time, these low flows occur in late July, August and early September. In low-water years, the result is a near-dry streambed condition for a short reach within known occupied habitat for Colorado squawfish. The river slowly recovers from this nearly dewatered state through groundwater accretions and small irrigation return flows, amounting to approximately 50 cfs within 2 miles of the diversion. Five miles below the diversion, flows increase to 200 cfs and, just above the confluence of the Gunnison River (IS miles downstream), flows reach 300-350 cfs (Reclamation, 1980). Depletions resulting from the sale and use of Ruedi Round II and Green Mountain Reservoir water will also result in some alteration of physical habitat in occupied habitat areas of the Colorado River below the confluence of the Gunnison River. The specific impacts that would result to this reach of the Colorado River from such a reduction are undetermined at this time, although the depletion of water will contribute to an additive loss of habitat below the Gunnison. It is assumed that the flows contributed by the Gunnison River and other tributaries will prevent a condition as critical as that found in the IS-mile reach. Therefore, for the purposes of this opinion, analysis of the water depletion impacts on Colorado squawfish resulting from the Ruedi II/Green Mountain water sales will concentrate on the IS-mile reach above the confluence of the Gunnison River.