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<br />OOlG58 <br /> <br />diameter upstream of the valve, or elevation 5722 [2]. This equation produces a maximum <br />discharge of 4,205 ft3/s at the maximum reservoir water surface elevation 6101.6, or about 3 <br />percent greater than the discharge curve indicates, and a discharge of 4,110 ft3/s at elevation <br />6085. <br /> <br />, <br />I. <br />t' <br /> <br />Maximum losses are normally assumed for the development of discharge curves when field data <br />are not available, while minimum losses are normally used to determine energy dissipation <br />requirements. Maximum losses are used throughout this analysis. The Project Data information <br />for Navajo Dam [3] cites an outlet works discharge capacity of 4,200 ft3/s at elevation 6101.5, <br />which corresponds closely to the discharge equation result. Operation of the main outlet works <br />above 3,200ft3/s would require removal of the current flow restriction, however. <br /> <br />Assuming an outlet discharge of 4,000 ifls and a reservoir water surface at elevation 6065 (using <br />the discharge equation), flow velocities, pressure heads, and cavitation indices were computed at <br />various locations within the main outlet works, as shown in table 1 below. The cavitation index is <br />defined as: <br /> <br />sigma = (Po - Pv) 1 (p V/12) <br /> <br />with Po equal to the absolute water pressure at a point (in Ib/ft2), or gauge pressure plus <br />atmospheric pressure, Pv equal to the absolute vapor pressure of water (in Ib/ft2), p equal to the <br />density of water (in slug/ft3), and Vo equal to the flow velocity at a point (in ftJs) [4]. For these <br />estimates, atmospheric pressure at the dam is assumed to be 1,728 Ib/ft2, the unit weight of water <br />is 62.4lb/ft3 (for converting head in feet to water pressure in Ib/ft2), Pv is 261b/ft2, and p is 1.94 <br />slug/ft3. The pressure heads at these locations were estimated using the detailed hydraulic loss <br />computations provided by the Technical Record of Design and Construction, assuming maximum <br />losses and applying an adjustment for the larger (4,000 ft3/s) discharge [2]. <br /> <br />Table 1. - Hydraulic Characteristics at Various Locations, Main Outlet Works <br />(Based on 4,000 ft:3/s discharge, RWS EJ. 6065, and maximum losses) <br /> <br />LOCATION AREA VELOCITY GAUGE HEAD CAV. INDEX <br />U/S elbow, "- 59.4 ft2 67.3 ftJs 215 ft 3.4 <br />8'-8-3/8" dia. <br />Fixed-wheel gate, 78.0 fl? 51.3 ftJs 224 ft 6.1 <br />6' by 13' <br />D/S end, 110" 66,0 fl? 60.6 ftJs 129 ft 2.7 <br />diameter pipe <br />D/S end, two 72" 28.3 fl? 70.7 ft/s 68 ft 1.2 <br />diameter pipes <br /> <br />3 <br />