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<br />001664 <br /> <br />are shown for three reservoir heads (274,315, and 374 feet)~ and for a range of gate openings (in <br />percent). Normal operations include power plant releases around 1,200 ft3/s, with both 72-inch <br />hollow-jet valves closed and with downstream tailwater levels around elevation 5711 as shown on <br />figure 2. The City ofFannington reports that the units experience notable cavitation at pressures <br />less than 90 Iblin2 (or net heads less than 208 feet), and for flows less than 350 f.t3/s per unit. <br /> <br />Hydraulic losses upstream of the units were computed and are summarized in Appendix B. <br />Hydraulic loss computations for both the main outlet works and the power plant were combined <br />for concurrent operation, usingwye branch loss coefficients proposed by Williamson and Rhone <br />[10]. Maximum discharge capacities were determined at reservoir elevation 6085 of3,650 ft3/S <br />through the two 72-inch hollow-jet valves, and 800 ft3/S through the power plant, for a combined <br />discharge capacity of 4,450 ff/s, or 340 ff/s greater than for operation of the hollow-jet valves <br />alone (about 8 percent). However, the net head on the units for this operating condition would be <br />only about 126 feet (or 55 Iblin2 pressure), due to the higher upstream losses and downstream <br />tailwater. Limiting operation of the hollow-jet valves to meet the minimum head requirement for <br />the units (208 feet) would result in a combined discharge capacity of only 3,650 f.t3/s, or 11 <br />percent less than for the hollow-jet valves alone. This reduction in discharge capacity becomes <br />greater at lower reservoir levels. Operation of the power plant is therefore not recommended <br />during maximum reservoir releases. <br /> <br />E. Maximum Discharge Capacities for All Features <br /> <br />Based on the recent biology studies of the SJRRIP, peak releases of 6,000 ft3/S from Navajo Dam <br />are desired for one to three weeks in May and June of each year. Minimum and maximum <br />historical reservoir elevations for May and June were identified for the past 35 years, from 1963 <br />through 1997, and are shown in table 2. Average reservoir elevations range from a minimum of <br />about 6030 feet in May, to a maximum of about 6050 feet in June. Maximum discharge capacities <br />for the existing outlet works corresponding to these reservoir levels are summarized in table 3 <br />below, using both the discharge curves and the flow equations for maximum losses. These <br />discharges assume all outlet gates and valves are fully open, without power plant operation, and <br />there are no operating restrictions for the outlet works. <br /> <br />Actual outlet discharges are expected to fall somewhere within the ranges shown in table 3, for <br />the operating conditions assumed. Table 3 demonstrates that the desired 6,000 ff/s peak release <br />from Navajo Dam in May and June cannot be met using the existing main and auxiliary outlet <br />works alone. Supplemental releases to the San Juan River necessary to meet a 6,000 ft3/S <br />downstream requirement for these normal reservoir levels would seem to be most easily met by <br />using the available wasteway capacity of the canal outlet works. The Cutter Dam spillway and <br />river outlet works can release up to a maximum of about 2,570 ft3/S, which is more than enough <br />for the desired total release. Some channel improvements may be required along Largo Canyon, <br />however, requiring additional studies beyond the scope of this analysis. <br /> <br />8 <br />