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378-2 Pond <br />Drainage area. The drainage area <br />above the pond must be protected <br />against erosion to the extent that <br />expected sedimentation will not <br />shorten the planned effective life <br />of the structure. For Livestock <br />Water Tanks the drainage area <br />shall be large enough so that <br />surface runoff and groundwater <br />flow will maintain an adequate <br />_supply of water in the pond. The <br />quality shall be suitable for the <br />water's intended use. <br />Reservoir area. The topography <br />and soils of the site shall permit <br />storage of eater at a depth and <br />volume that ensure a dependable <br />supply, considering beneficial <br />use, sad mentation, season of use, <br />and evaporation and seepaoe <br />I osses. If surface runoff i s file <br />primary source of water for a <br />pond, the soils shall be <br />impervious enough to prevent <br />excessive. seepage losses or shall <br />be of a type that sealing is <br />practicable. <br />Ponds for fish shal I have a <br />minimum size of one-quarter <br />surface acre. No more than 20% of <br />the area sfiould have water depths <br />less than 2 feet. Fish-out and <br />rearing ponds may be smaller and <br />shallower. <br />Gepth.along the shoreline of fish <br />ponds should slope abruptly into <br /><3) feet of water. In addition, <br />ponds where fish will be <br />overwintered: <br />(1> celow 6,000 feet, should have <br />a minimum depth of 6 feet over <br />one-third of the pond area. <br />(2) Above 6,000 feet, should have <br />a minimum depth of 10 feet over <br />one-third of the pond area. Where <br />a live stream or aerated spring <br />water flows continuously into a <br />pond, the minimum depth required <br />is 7 feet over one-third of the <br />pond area. <br />Spacing. Reasonably dependable <br />livestock water in a pasture <br />bounded. by fences or a natural <br />livestock barrier should not be <br />located closer together than (1) <br />one-quarter to one-half mile in <br />rough mountain land, (2) three- <br />eighths to three-fourths of a mile <br />in foothills or rolling land, or <br />(3) three-quarters to one mile in <br />undulating prairie land. <br />Design criteria for embankment <br />ponds <br />Foundation cutoff. A cutoff of <br />relatively impervious material <br />shall be provided under the dam. <br />The cutoff shall be ,ocated at or <br />upstream from the centerline of <br />the dam. It shall extend up the <br />abutments as required and be dee~ <br />enough to extend into a relatively <br />impervious layer or provioe for a <br />stable dam when combined with <br />seepage control. The cutoff <br />trench shall have a bottom width <br />adeouate to accommodate the <br />equipment used for excavation, <br />bacxfill, and compaction <br />operations. Side slopes shall not <br />be steeper than one horizontal to <br />one vertical. <br />Seepage control. Seepage control <br />is to be included if (1) pervious <br />layers are not intercepted by the <br />cutoff, (2) seepage would create <br />swamping downstream, (3) such <br />control is needed to insure a <br />stable embankment, or (4> special <br />problems require drainage for a <br />stable dam, seepaoe may be <br />controlled by <1) founoation, <br />abutment, or embankment drains; <br />(2) reservoir blanketing; or (3) <br />combination of these measures. <br />SCS, Colorado, January 1989 <br />