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<br />because the crest elevation may be lower than the storage level. <br /> <br /> <br />This is a consideration when there are limitations on spillway crest <br /> <br /> <br />length or maximum water surface elevation. <br /> <br />(2) Project objectives and flexibility. . Gated spillways permit a <br />wide range of releases and have capability for preflood drawdown. <br /> <br />(3) Operation and maintenance. . Gated spillways experience more <br /> <br /> <br />operational problems and are more expensive to maintain than ungated <br /> <br /> <br />spillways. Constant attendance or several inspections per day by an <br /> <br /> <br />operator during high water levels is highly desirable for reservoirs <br /> <br /> <br />with gated spillways, even when automatic or remote controls are <br /> <br /> <br />provided, and should be required during periOdS of major flood <br /> <br /> <br />inflows where automatic or remote controls are not provided, Gated <br /> <br /> <br />spillways are more subject to clogging from debris and jamming from <br /> <br /> <br />ice, whereas, properly designed ungated spillways are basically free <br /> <br /> <br />from these problems. Gated spillways require regular maintenance, <br /> <br /> <br />and, as a minimum, an annual operation test for safety purposes. <br /> <br />(4) Reliability.. The nature of ungated spillways reduces dam <br /> <br /> <br />failure potential associated with improper operation and mainte- <br /> <br /> <br />nance. Where forecasting capability is unreliable, or where time <br /> <br /> <br />from the beginning of runoff to peak inflow is only a few hours, <br /> <br /> <br />ungated spillways are preferred, particularly for high hazard <br /> <br /> <br />structures. Consequences of failure of operating equipment or <br /> <br /> <br />errors in operation are more severe in such cases. <br /> <br />(5) Data and control requirements. . Gated spillways require <br />reliable realtime hydrologic and meteorologic. data to make proper <br />regulation possible. <br /> <br />20 <br />