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I I I I I I I I I I I I I I I I I I I functionally comparable to the Dolores River in the life of the Colorado squawfish. Habitat suitability of the Dolores River for different life stages of Colorado squawfish is summarized in Table 33. Physical factors that affect the suitability of five parameters listed in Table 33 are discussed below. 4.3.1.1 Flows. The Dolores River drainage exhibits a hydrograph that is typical of most upper Colorado River basin drainages. Beginning in mid to late March, flows increase dramatically from melting of mid-elevation snowpack. This early runoff can peak quickly and subside in mid to late April, when flows increase again with melting of higher elevation snowpack. Following spring runoff, flows gradually subside until mid to late July. From late July through September, the climate in the Dolores River drainage is often dominated by moisture-laden Pacific air masses transported by a southwesterly flow of air. The result of this "summer monsoon season" is frequent high intensity storms that result in short term flow of relatively large magnitude. For purposes of assessing flows of the Dolores River, the study area was divided into two regions, each with a distinct hydrograph. These regions included: 1) the Dolores River above the confluence of the San Miguel River (above RM 64.4), and 2) the Dolores River below the confluence of the San Miguel River (below RM 64.4). RM 0.0 to 64.4. Below the confluence of the Dolores and San Miguel rivers, flow increased substantially. The San Miguel River was a free flowing river with a relatively normal hydrograph, and an average annual flow of 410 cfs. Peak flows from the San Miguel River generally occurred in late April and early May and ranged from below 1000 to above 8000 cfs for the period of record. Base flows generally occurred in late fall and winter and averaged 80 to 200 cfs. Irrigation withdrawals from the San Miguel above Uravan affected flows during the summer months. Peak instantaneous flow and peak daily discharge at the gage near Cisco on the Dolores River in 1990 were 1,340 cfs (on July 18) and 997 cfs (on June 12), respectively. In 1991, peak daily discharge at the same location was 2,130 cfs on May 22. During 1990, flows from the San Miguel River contributed more to the system than flows from the Dolores River below McPhee Dam. Flows encountered in the Dolores River near its confluence with the Colorado River during the study period ranged from 107 to 1400 cfs (Table 34). Drought conditions persisted for both years of the study. Figure 10 presents a post-dam hydrograph of mean monthly flows of the Dolores River near its confluence with the Colorado River. Also presented are mean daily flows for the 2 years of study. Low flows during the study were a result of below normal snow pack in both the Dolores and San Miguel rivers. McPhee Dam captured runoff during both years and compounded low flow conditions. These conditions probably impeded fish movement between reaches and habitats. Numerous cobble bars were encountered with only 5-7 em of water. Colorado squawfishcaptured in the lower 2 kID of the Dolores River may have been prevented from moving higher in the drainage by such conditions just upstream of the confluence with the Colorado River. Mean monthly flows of the Dolores, White and Yampa rivers were compared in Figure 11 to provide a prospective on the relative size of the Dolores River after McPhee Dam. The White River is a tributary of the Green River very similar in size and sediment characteristics to the Dolores River, and supports adult Colorado squawfish. The Dolores River averaged higher spring peak flows than the White River, but base flows in the White were consistently higher. Spring runoff in the White River generally peaked in June compared to May for the Dolores River. The Yampa River is the major tributary of the Green River and is known to provide both holding and spawning habitat 11