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<br />Pti emergency spillway may be advisable to accommodate flows resulting <br /> <br /> <br />from misoperation or malfunction of othe~ spillways and outlet works, <br /> <br /> <br />may be sized to accommodate a flood smaller than the IOF but one which <br /> <br /> <br />could reasonably follow the IOF, or to avoid overtopping the dam by the <br /> <br /> <br />occurrence of the PMF when an IDF smaller than the PMF has been appro- <br /> <br /> <br />priately selected. The crest of an emergency spillway should be set <br /> <br /> <br />above the maximum water surface (attained when accommodating the IOF) <br /> <br /> <br />SO it will not overflow as a result of reservoir setup and wave action. <br /> <br /> <br />The design of an emergency spillway should.be subject to the following <br /> <br /> <br />limitations: <br /> <br />. The structural integrity of the dam should not be jeopardized <br />by spillway operation. <br /> <br />.' Large conservation storage volumes should not be lost as a <br /> <br /> <br />result of degradation of the crest during operation. <br /> <br />.. The effects of a downstream flood resulting from uncontrolled <br /> <br /> <br />re.lease of reservoir storage shoul d not be greater than those <br /> <br /> <br />caused by the IOF without the dam. <br /> <br />Outlet works used in passing floods and evacuating reservoir storage <br /> <br /> <br />space should be designed for frequent use and should be highly reliable. <br /> <br /> <br />Reliability is dependent on foundation conditions which influence <br /> <br /> <br />settlement and displacement of waterways, on structural competence, on <br /> <br /> <br />susceptibility of the intake and conduit to plugging, hydraulic effects <br /> <br /> <br />of spillway discharge, and operating reliability. <br /> <br />23 <br />