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<br />, <br /> <br />0024j7 <br /> <br />Flume: Flumes are shaped, open-channel flow sections that force flow to accelerate. <br />Acceleration is produced by converging the sidewalls, raising the bottom, or a <br />combination of both. <br /> <br />Long-throated: Long-throated flumes control discharge rate in a throat that is <br />long enough to cause nearly parallel flow lines in the region of flow control. <br />Parallel flow allows these flumes to be accurately rated by analysis using fluid <br />flow concepts. The energy principle, critical depth relationships, and boundary <br />layer theory are combined to rate flumes and broad-crested weirs by Ackers et aI <br />(1978) and Bos et al. (1991). Thus, these flumes and modified broad-crested weirs <br />shown in figure 1 are amenable to computer calibrations. Long throated flumes <br />can have nearly any desired cross-sectional shape and can be custom fitted into <br />most canal-site geometries. The Ramp flume, also considered a version of <br />broad-crested weirs, is an example of this kind of flume. <br /> <br />Parshall Flume: A Parshall flume is a specially shaped open channel flow <br />section that may be installed in a drainage lateral or ditch to measure the rate of <br />flow of water. <br /> <br />~ <br /> <br />Short-throated: Short-throated flumes are considered short because they control <br />flow in a region that produces curvilinear flow. While they may be termed short-- <br />throated, the overall specified length of the finished structure including transitions <br />may be relatively long. The Parshall flume is the main example of this kind of <br />flume. These flumes would require detailed accurate and accurate knowledge of <br />the individual streamline curvatures for calculated ratings which is usually <br />considered impractical. Thus short-throated flumes are determined empirically by <br />comparison with other more precise and accurate water measuring systems. <br /> <br />-I <br />I <br /> <br />I <br /> <br />Forebay: The body of water immediately upstream from a powerplant. <br /> <br />Foundation, dam: The excavated surface upon which a dam is placed. <br /> <br />Foundation drains: Tile or pipe for collecting internal seepage water of dam. <br /> <br />Freeboard: The difference in elevation between the maximum reservoir water surface <br />and the dam crest. <br /> <br />Freeze-thaw damage: Damage to concrete caused by extreme temperature variations as <br />noted by random pattern cracking. Damage is accelerated by the presence of water and <br />commonly more severe on the south-facing side of structures. <br /> <br />G <br /> <br />Gallery: A passageway within the body of a dam, its foundation, or abutments. <br /> <br />Gate: A device that controls the flow in a conduit, pipe, or tunnel without obstructing <br />any portion of the passageway when in the fully open position. <br />