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<br />001075 <br /> <br />to and including 47-3/4 inches. To provide a margin of safety, the maximum gate <br />opening should be limited to 47-1/2 inches. The auXiliary outlet is used only when it is <br />necessary to take the river outlet works out of service. At the present reservoir elevation <br />about 1,500 cfs can be released through the auxiliary outlet at a 47-1/2-inch gate <br />opening. The minimum flow requirement in the San Juan River at Navajo Dam is 500 <br />cfs. Therefore, the 47-1/2-inch gate opening restriction will not create a river regulation <br />problem. <br /> <br />At a gate opening of 48-1/2 inches" the water jet filled the downstream gate frame, cut off <br />airflow from the air supply pipe, and pressures under the jet reached 24.5 feet below <br />atmospheric pressure. Although no damage to the concrete conduit occurred during test <br />releases, prolonged operation at severe subatmospheric pressures would create a definite <br />potential for cavitation damage. <br /> <br />A follow-up inspection for cavitation damage in the auxiliary outlet works performed by Tom <br />Isbester and Lee Gerbig from Denver in 1979 found the auxiliary outlet works to be in "excellent <br />condition" [5]. ~ <br /> <br />2. Gas supersaturation modifications. - <br /> <br />Operation of the auxiliary outlet works after the air slot was installed resulted in high levels of gas <br />supersaturation in the downstream channel. Field tests conducted in 1972 [15, 17] found nitrogen <br />supersaturation levels exceeding 130 percent in the stilling basin. The tests also showed operation <br />of the 30-inch hollow-jet valve from the main outlet works produced nitrogen supersaturation <br />levels of 120 percent. As a result, a model study [18] was conducted in 1976 to determine a <br />method of reducing the gas supersaturation levels in the spillway stilling basin caused by operation <br />of the outlet works. The model study recommended a flip lip be placed at the exit of the free flow <br />tunnel for the auxiliary outlet works, and the angle of the 30-inch hollow-jet valve be changed <br />from 24 degrees to 15 degrees. The purpose of both modifications was to reduce the penetration <br />depth of outlet works flows into the spilJway stilling basin. The modifications were completed <br />and field tested in 1977 [19]. These tests showed gas supersaturation levels were reduced to a <br />maximum of about 112 percent. The tests resulted in no limitations on auxiliary outlet works <br />operation with respect to gas supersaturation. <br /> <br />IV. Current Condition of Mechanical Features <br /> <br />A. Main Outlet Works <br /> <br />1. 6- by 13-foot fixed-wheel gate. . The 6- by 13-foot fixed-wheel gate was designed to provide <br />emergency and maintenance control of the main outlet works. The gate is equipped with six steel <br />wheels on each vertical side that roll on vertical steel rails embedded in the concrete. The gate is <br />connected to a hydraulically-operated cylinder which is located at the top of the dam. A series of <br /> <br />18 <br />