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<br />4. Brldqes. Bridges should be designed for overtopping In accordance <br />with the criteria of the Drainage Criteria Manual and according to <br />the desIgnated street use. <br /> <br />5. Culverts. Culverts will be used in lIeu of brIdges where feasible. <br />Backwater effect of culverts to be consistent with channel require- <br />ments and adjacent topography. Energy dissIpators must be used <br />downstream of culverts wherever the flow velocity exIt from the <br />culvert exceeds the allowable channei velocity. <br /> <br />a. The use of armor piatlng on culvert floors must be considered <br />when the potential for wear by movin!l rocks and hIgh velocities <br />exists. <br /> <br />6. Conduits. Conduits are designed b'lsed upon the criteria included <br />in the storm sewers and the major drainage parts of the Denver <br />Regional Council of Governments Manual. <br /> <br />a. The maximum allowable veiocl ty for a non-armored concrete <br />conduit shall be about 20 fps. <br /> <br />b. On steep slopes, velocity may be controlled by artlfically <br />created head losses due to manholes and/or bends. <br /> <br />c. When it is desirable to achieve a velocIty about 20 fps, the <br />lower portion of the conduit shall be armored with steei sheet, <br />ralls, etc. <br /> <br />d. The hydraul ic grade lIne shall be maintained below the ground <br />surface. <br /> <br />7. Irrlqatlon Ditches. All Irrigation ditches and laterals will be <br />provIded for, though laterals ',01111 not be shown on master plans. <br />Use on-grade fiumes where feasible to reduce silt and maintenance <br />problems. Capacity of crossings wIll be limited to cause storm <br />runoff In ditches to enter wat,orways. II"rlgatlon ditch crossIngs <br />will be designed to obvIate pkkin" up of overflow from waterways. <br /> <br />8. Drops and Checks. Channel drops will be used as needed to control <br />the hydraulic grade I ine and velocity to within reasonable slopes <br />and lImits. Drops will be of concrete, rlprap, or rlprap in ga- <br />blons, be of pleasing appearance, have gravel filter blankets under <br />the rock to control undercuttln", and be properly notched for the <br />trickle channel. DesIgn must account fOI" potential vandalism. <br />Checks will be end-protected to elimInate side cutting. <br /> <br />9. Enerqy Dissipators. These will usually consist of natural rock <br />Impact blocks with suitable rlprap or "ablon protected bottom and <br />side siopes. Design will account for potential vandalism. <br /> <br />'11-4 <br />