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<br />0024:i 5' <br /> <br />u <br /> <br />USGS: An acronym used for U.S. Geological Survey, the agency that monitors <br />strearnflows, river hydrology, and seismic activity. <br /> <br />Unbalanced head condition: See "differential head condition." <br /> <br />Uplift pressure: See "pore-water pressure." <br /> <br />Upstream face: The inclined surface of the dam that is in contact with the reservoir. <br /> <br />v <br /> <br />Valve: A device used to control the flow in a conduit, pipe, or tunnel that permanently <br />obstrUcts a portion of the waterway. <br /> <br />Valve, butterfly: A valve designed for quick closure that consists of a circular leaf, <br />slightly convex in form, mounted on a transverse shaft carried by two bearings. <br /> <br />Valve, gate: A valve with a circular-shaped closing element that fits securely over an <br />opening through which water flows. <br /> <br />Valve, hollow jet: A valve having a closing member that moves upstream to shut off the <br />flow. The hollow jet valve discharges a hollow or annular jet dispersed over a wide area. <br /> <br />-./ <br /> <br />Valve, tube: A valve which is opened or closed by mechanically moving a tube upstream <br />or downstream by an actuating screw. <br /> <br />Vortex: A revolving mass of water in which the streamlines are concentric circles and in <br />which the total head is the same. <br /> <br />w <br /> <br />Water conveyance structure: Any structure that conveys water from one location to <br />'another. <br /> <br />Waterstage recorder: A motor-driven (spring wound or electric) instrument for <br />monitoring water surface elevation. <br /> <br />Waterstop: A continuous strip of waterproof material placed at concrete joints designed <br />to control cracking and limit moisture penetration. <br /> <br />Weep hole: A drain embedded in a concrete or masonry structure intended to relieve <br />pressure caused by seepage behind the structure. <br /> <br />:-l <br /> <br />--, <br />.1 <br />~, ." . ,. <br /> <br />l;~,~, <br /> <br />, i <br />l...T <br />.r~1 <br /> <br />',-1 <br />~.~, i <br /> <br />,~ <br />I <br /> <br />I <br />., ! <br />