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378-3 Pond <br />n <br />U <br /> <br />i <br />Engineer and filed with and approved <br />by the State Engineer of Colorado <br />before construction begins. <br />Geology. Sufficient soil inves- <br />tigations shall be made of the struc- <br />ture site and borrow areas to deter- <br />mine its suitability for meeting the <br />conservation needs. <br />Foundation cutoff. A cutoff of <br />relatively impervious material shall <br />be provided under the dam. <br />Cutoff shall be located aE or up- <br />stream from the centerline of the <br />dam. It shall extend up the abut- <br />ments as required and shall have a <br />minimum depth of four (4) feet, but <br />it shall be deep enough to extend <br />into a relatively impervious layer or <br />provide for a stable dam when com- <br />bined with seepage control. The <br />cutoff trench shall have a minimum <br />bottom width of five (5) feet and <br />shall be adequate to accomodate the <br />equipment used for excavation, back- <br />fill and compaction operations. Side <br />slopes shall not be steeper than <br />1:1. <br />Seepage control. Seepage control <br />is to be included if (1) pervious <br />layers are not intercepted by the <br />cutoff, (2) seepage may create swamp- <br />ing downstream, (3) needed to insure <br />a stable embankment or (4) special <br />problems require drainage for a <br />6[able dam. Seepage control may be <br />accomplished by (1) foundation, abut- <br />ment, or embankment drains; (2) <br />reservoir blanketing; or (3) a com- <br />bination of these measures. <br />Earth embankment. The minimum <br />top width for a dam is shown below: <br />Total Height <br />of embankment Top Width <br />(f t.) (f t.) <br />14 or less 8 <br />15-19 10 <br />20-24 12 <br />25-34 14 <br />35 or more 15 <br />Note: For this standard, the maximum <br />effective height of the dam is 35 fL. <br />If the embankment top is to be used as <br />a public road, the_minlmum width shall <br />be 16 ft. for one-way traffic and 26 <br />ft. for two-way traffic. Guardrails <br />or other safety measures shall be used <br />where necessary and shall meet the <br />requirements of the responsible road <br />authority. <br />The combined upstream and downstream <br />side slopes of the settled embankments <br />shall not be less than 5 horizontal to <br />1 vertical. All slopes must be de- <br />signed to be stable, even if flatter <br />side slopes are required. The up- <br />stream slope shall never be steeper <br />than 2 1/2:1, and the downstream slope <br />shall never be steeper than 2: 1. How- <br />ever, dams constructed of silty and <br />silty sand soils (ML's and SH's) shall <br />have both the upstream and downstream <br />slopes not steeper than 3:1. <br />When it is necessary to use rocky <br />soils for the embankment, the dam <br />shall be designed as a "zoned" fill, <br />using the finer grained most imper- <br />vious materials for the center or <br />upstream two-thirds of the dam and <br />placing the rocky soils on the down- <br />stream slope. <br />If needed to protect the face of the <br />dam, special measures, such as berms, <br />rock riprap, sand-gravel, soil cement, <br />log booms or special vegetation (TR- <br />SCS, Colorado, April 1980 <br />