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<br />• <br />• <br />378-4 Pond <br />56) shall be provided. <br />The minimum elevation of the top of <br />the settled embankment shall be one <br />(1) foot above the eater surface in <br />the reservoir with the emergency <br />spillway. flowing at design depth. <br />The minimum difference in elevation <br />between the crest of the emergency <br />spillway and the settled top of the <br />dam shall be two (2) feet; except <br />that the minimum depth of the emer- <br />gency spillway shall never be less <br />than the Colorado State Eagineer's <br />requirements. In the case of Live- <br />stock Water Tanks and Erosion Control <br />Dams, the settled elevation of the <br />top of the dam at all points shall be <br />not less than four (4) feet above the <br />crest of the spillway. <br />The design height of the dam shall be <br />increased by the amount needed to <br />insure that, after settlement, the <br />height of the dam equals or exceeds <br />the design height. This increase <br />shall not be less than 5 percent. <br />The allowance for settlement will be <br />based on centerline height. <br />Pzincipal spillway. A pipe <br />conduit, with needed appurtenances, <br />shall be placed under or through the <br />dam in all cases where required by <br />the State Engineer of Colorado. In <br />other cases, a pipe conduit is re- <br />quired unless :he rate and duration <br />of flow can be safely handled by a <br />vegetated or earth spillway or where <br />a rock, concrete, or other type of <br />mechanical spillway is used. <br />For Livestock Water Tanks, should the <br />State Engineer of Colorado so re- <br />quire, there shall be located beneath <br />the dam an outlet pipe not less than <br />eight (8) inches in diameter equipped <br />with a control valve attached to the <br />upstream end of the pipe, together <br />with suitable mechanism for operating <br />the valve. <br />SCS, Colorado, April 1980 <br />For Erosion Control Dams, there shall <br />be located beneath the dam an ungated <br />outlet pipe not less than twelve (12) <br />inches in diameter and large enough <br />to drain vi thin thirty-six hours any <br />impoundment in excess of two (2) <br />acre-feet. <br />When a 'pipe conduit is needed to <br />protect the emergency spillway from - <br />prolonged saturation by continuous <br />floods, floe from springs, or low <br />floes that may continue for several <br />days during snovmelt or following a <br />storm, a trickle tube not smaller than <br />12 inches in diameter shall be <br />installed through the dam. <br />When a principal spillway is needed to <br />reduce the frequency of operation of <br />the emergency spillway, the minimum <br />capacity shall be adequate to carry a <br />2 year frequency, 24-hour discharge. <br />Where the emergency spillway is <br />founded in erosive soils (SM, SP or <br />SW), this minimum capacity shall be <br />increased to at least a 5 year fre- <br />quency, 24-hour duration discharge. <br />These discharges may consider effect <br />of reservoir storage. <br />When determined that a principal <br />spillway or trickle tube conduit is <br />required, the crest elevation shall <br />not be less than 0.5 feet below the <br />crest of the emergency spillway for <br />dams having a drainage area of 20 <br />acres of less and not less than one <br />(1) foot for those having a drainage <br />of more than 20 acres. <br />If the pipe conduit diameter is [en <br />(10) inches or greater, its design <br />discharge may be considered when cal- <br />culating the peak outflow rate through <br />the emergency spillway. However, in <br />this instance, the crest elevation of <br />the pipe conduit of the inlet shall be <br />of such that the full floe will be <br />generated in the conduit before [here <br />is discharge through the emergency <br />~, <br />