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16 >j I Historically, the Grand Valley was a congregation area during spawning for both the Colorado squaw fish and razorback sucker (Quartarone, 1993), and it still contains more adult Colorado squaw fish than any other part of the Colorado River (Osmundso~ and Kaeding, 1989; Osmundson et al., 1995). Razorback suckers are now very rare in this reach (Osmundson and Kaeding, 1991), therefore this research focuses on the habitats of the Colorado squawfish. Flows of the Colorado River in the Grand Valley are affected by 24 reservoirs with a capacity greater than 5,000 acre-feet (6,167,000 cubic meters), and numerous water diversions (Liebermann et al., 1989). Although water development has caused some changes in the river's flow, spring runoff is still largely controlled by snowmelt. Snowmelt usually begins in April, peaks near the beginning of June, and is nearly complete by the end of August. During low flow in August, flows are largely controlled by dams and diversions, and over one half of the river's discharge can be diverted for irrigation upstream of the study area (U.s. Geological Survey (USGS) gauge records). The two gauges which provide long term flow records for the study area are: 1) the Cameo gauge which is approximately 18 kilometers (11 mi) upstream of the study area; and 2) the Colorado-Utah State line gauge which is approximately 34 kilometers (21 mi) downstream of the study area (Figure 2.1). The climate of the region is arid with an annual precipitation of approximately 22.4 centimeters (8.8 in) per year, distributed fairly evenly throughout the year. The driest season is December-February where on average there is 1.4 centimeters (0.5 in) of precipitation per month, and the wettest season is August-October which averages 2.2 centimeters (0.9 in) per month. This late summer precipitation usually is from intense :\ J -1 ; I ., ~.'....... ~:~:. -';:.... I J.... ., J I j J J .1 ] ) J