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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />2. A low flow channel is provided to carry normal low flows at non- <br />silting velocities. <br />3. Side slopes of trapazoidal channel sections not to be steeper <br />than 1.5 to l, and should preferably be 2 to 1 where space is <br />available. Vertical side walls may be used. <br />4. Sloping side and bottom lining is at least 8 inches thick. <br />Vertical walls at least 12 inches thick. <br />5. Channel freeboard is 1.5 feet under maximum flow conditions. <br />6. Concrete-lined channels are underdrained to prevent hydrostatic <br />uplift. <br /> <br />Closed Conduits <br /> <br />1. The conduit invert slope is steep enough to maintain super- <br /> <br /> <br />critical flow. <br /> <br /> <br />2. Large radius bends are used where alignment changes are necessary. <br /> <br /> <br />Miter bends should not be used. <br /> <br /> <br />3. A bell shaped conduit entrance is used to minimize hydraulic <br /> <br /> <br />losses. <br /> <br /> <br />4. A stilling basin is provided at the lower end of the conduit to <br /> <br /> <br />dissipate the energy of the high velocity flow and thereby mini- <br /> <br /> <br />mize downstream channel erosion. <br /> <br /> <br />5. Conduits are designed for at least the American Association <br /> <br /> <br />of State Highway Officials H-20 live load plus dead load of <br /> <br /> <br />overlying earth and pavement, plus a 250 pounds per square <br /> <br /> <br />foot uniform overlying dead load for possible future grade <br /> <br /> <br />changes. <br /> <br />Detention Dams <br /> <br />1. Flood detention dams are designed to meet the requirements of <br /> <br /> <br />the State of Colorado. <br /> <br /> <br />2. Dams are designed to detain the 100-year flow without having the <br /> <br /> <br />maximum reservoir water level overflow the spillway crest. <br /> <br /> <br />3. Spillways are designed to pass the 6-hour probable maximum pre- <br /> <br /> <br />cipitation, PMP, flood without overtopping the dam. <br /> <br /> <br />4. Spillways are provided with stilling pools to dissipate the <br /> <br /> <br />energy of high velocity flow to minimize downstream channel <br /> <br /> <br />erosion. <br /> <br />-52- <br />