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flows greater than 2,500 ft3/s would only occur under extreme situations. Actual7-day high flow releases to the Dolores River based upon operations of a full reservoir (1987- 1989) are as follows: May 87: 7 days greater than 2,319 ft3/s May 88: 7 days greater than 1,087 ft3 Is May 89: 7 days greater than 1,001 ft3/s The construction of McPhee Dam has no effect upon inflows from side drainages in the study area. The only streamflow record for tributaries to the Dolores River below McPhee is for Disappointment Creek. The 1.5-year 7-day high flow for Disappoint- ment Creek near Dove Creek was 104 ft3/s. No data are available for other tributaries to the Dolores River. Table 7 is an estimate of post-dam l.5-year recurrence interval discharges for selected locations on the Dolores River within the study area. The low flow or baseflow of natural free-flowing rivers results from subsurface (ground water or interflow processes) discharges occurring within the drainage basin. These processes are critical for sustaining perennial flow in river systems during periods of low precipitation. Ifbaseflows are depleted, the river becomes intermittent and the resources dependent on the perennial flow, such as fisheries, are lost or significantly reduced. The baseflow of a river system can be affected by various processes occurring within the drainage basin. As a river flows downstream, baseflow can increase from additional ground water inflow (effluent river system) or decrease through recharge to ground water systems (influent river system). Other common losses to baseflow are man-related consumptive water uses, evaporation from the water surface and channel banks, and transpiration from riparian vegetation. The Colorado Water Conservation Board has ftled an instream flow right for 78 ft3 Is between McPhee and the confluence with the San Miguel River. This flow rate was detennined from data collected by the Colorado Division of Wildlife near the Bradfield Ranch in the early 1970's (personal communication, Norwin Smith, Colorado Division of Wildlife, 1989). According to the Colorado Water Conservation Board's Instream Flow Appropriation Tabulation, the 78 ft3 Is flow is applicable to the reach between McPhee Dam and the confluence with the San Miguel River. The subject study area is nested within this reach. According to the USBR's bypass release schedule, 78 ft3/s would only be released in an above-average water year. In average and below average water years, the minimum release would be 50 and 20 ft3/s, respectively. Wet-, normal-, and dry- year release schedules were discussed earlier in this section. To determine low flows necessary to protect resource values defined by BLM, streamflow gains or losses were identified in the study area. In Figures 11,12, and 13, 1989 summer flows at McPhee Dam are plotted against those at Bedrock. Starting around mid-May 1989, the dam release was gradually reduced from 600 ft3/s to approximately 78 ft3/s on June 6. It took about 20 days, until June 26, for the flows at Bedrock to stabilize at around 60 ft3 Is. This time lag resulted from the slow release of channel bank storage, slow streamflow velocities, and some precipitation that occurred on June 10 and 12. It is also possible that seasonal water diversions were Table 7. 1.5- Year Recurrence Interval Flow Estimates for the Dolores River at Selected Locations Post-McPhee Dam Location Post-Dam Bank-full (ft3/s) Bradfield Bridge 1,000 Dove Creek Pump 1,000 Below Disappointment Creek 1,200 Below Gypsum Valley 1,300 Above La Sal Creek 1,400 At Bedrock 1,500 21