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<br /> <br />• <br />• <br />378-8 Pond <br />..not be steeper than 3 to 1 where <br />practical to obtain.) The minimum <br />width of spillway shall be 8 feet <br />except that for dams having an <br />effective height exceeding 20 feet, <br />the emergency spillway shall have a <br />bottom width of not less than 10 <br />feet. <br />Constructed spillways are open <br />channels and usually consist of an <br />inlet channel, a control section and <br />an exit channel. _ <br />Upstream from the control section, <br />the inlet channel shall be level for.. <br />the distance needed to protect .and <br />maintain the crest elevation of the <br />spillway. The inlet channel may be <br />curved to fit existing topography. _. <br />The exit channel should be straight <br />whenever possible. The grade of the <br />exit channel of a constructed spill- <br />way shall fall within the range <br />established by discharge requirements <br />and permissible velocities. <br />The exit channel shall extend to a <br />point well downstream from any part <br />of the embankment where the design <br />flow may be discharged without damage <br />to the earth embankment or a wingdike <br />shall be constructed to prevent flows <br />from encroaching on the downstream <br />toe of the dam. (The inlet and exit <br />channels may be flared, but the flare <br />will not be considered in capacity <br />computations.) <br />Structural emergency spillways. <br />If chutes or drops are used for <br />principal spillways or emergency <br />spillways, they shall be designed <br />according to the principles set <br />forth Sn the Engineering Field Manual <br />for Conservation Practices, National <br />Engineering Handbook, Section 5, <br />Hydraulics, Section 11, Drop Spill- <br />ways, and Section 14, Chute Spill- <br />ways, as applicable. The minimum <br />SCS, Colorado, April 1980 <br />capacity of a structural spillway <br />shall be that required to pass tfie <br />peak flow expected from a design <br />storm of the frequency and duration <br />shown in Table 3 less any reduction <br />creditable io conduit discharge and <br />detention storage. <br />Instrumentation. Any new dam <br />where the effective height exceeds 25 <br />feet or where the total volume at the <br />crest of the emergency spillway ex- <br />ceeds 500 acre-feet, shall have the <br />following instrumentation: <br />1. Monuments to measure the horizon- <br />_tal.and vertical movement of the dam. <br />. 2.__..Seepage. or leakage measuring de- <br />vices for drains. <br />Concurrent ;reservoir level readiags <br />shall be recorded during monitoring of <br />the instrumentation. <br />A schedule of monitoring the instru- <br />mentation shall be recommended to, and <br />the responsibility for accomplishing <br />the same established by, the owner. <br />Instrumentation provisions sad the <br />schedule will be subject to approval <br />by the Colorado State Engineer. <br />Borrow. If additional materials, <br />other than will be obtained from the <br />foundation, cutoff and spillway exca- <br />vations, are required to construct the <br />embankment, borrow areas shall be <br />designated and shown on the plans. On <br />dams having an upstream slope steeper <br />than 3:1, no material shall De <br />borrowed within a distance of 50 feet <br />of any part of the dam. <br />On daps requiring special plans and <br />specifications for approval of the <br />State Engineer of Colorado, borrow <br />pits shall not be located closer than <br />200 feet from either toe of the em- <br />bankment nor below the high water line <br />of the reservoir unless written appro- <br />val of the Colorado State Engineer has <br />been obtained. <br />