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<br />I <br />I <br />I <br />I <br />I <br />I <br />I 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 />c. Maximum of 3:1 side slopes for the improved grass <br />lined channel. <br /> <br />d. Centerline curvatures of twice the channel top <br />width, with a 100 foot minimum. <br /> <br />e. Channel freeboard of one foot for the design storm. <br /> <br />f. Hydraulic roughness factors in accordance with the <br />Urban Storm Drainage Criteria Manual. <br /> <br />g. Froude number (turbulence factor) shall be less <br />than 0.80 whenever possible. <br /> <br />2. <br /> <br />Culverts - For the purposes of this report, culverts <br />are defined as structures with earth and cover between <br />the structure and the road surface. Protective measures <br />are often necessary in channels directly upstream and <br />downstream of culverts due to the increased velocity <br />through the culvert. <br /> <br />3. <br /> <br />Design of culverts shall be in accordance with the U.S. <br />Department of Commerce, Bureau of Public Roads, Hydraulic <br />Engineering Circulars No. 5 and 10 reflecting the effects <br />of inlet and outlet control. The reinforced concrete <br />box culvert, indicated on the preliminary plans, was <br />selected based upon the available information for clearances <br />between utilities and the selected design flow at that <br />point. Final design of culverts may often change the <br />size and type of material used as long as the design flow <br />established in the preliminary plan is passed within <br />the allowable he~dwater limits. Depths of flood flows <br />over streets should not exceed these spec.ified in the <br />Manual unless special conditions dictate. <br /> <br />Drop Structures - Drop structures are designated on <br />portions of the channel where a totally new channel cross <br />section must be constructed. Drop structures may be <br />constructed utilizing gabion baskets with rip rap pro- <br />tection above and below the drop. The use of suffi- <br />cient rip rap or river mats above and below the drop <br />structure is imperative to prevent erosion. Drop <br />structures must be of sufficient height to insure that <br />a well defined and efficient hydraulic jump will occur <br />below the drop for adequate energy dissipation. <br /> <br />Energy Dissi~ators - Energy Dissipators will be necessary <br />where exceSSlve velocities are developed due to high heads <br />behind culverts. These will usually consist of a natural <br /> <br />4. <br /> <br />VII-2 <br />