Laserfiche WebLink
a. Stabilizing all exposed surface areas to promote a reduction in the rate and <br />volume of runoff, <br />b. Using straw dikes, riprap, check dams, berms, geotextile materials, mulches, <br />vegetation sediment filters, contour furrows or other measures that reduce <br />overland flow velocity, reduce runoff volume, or trap sediment; or <br />Such other measures to minimize erosion resultant siltation and disturbance to the <br />prevailing hydrological balance. <br />Culverts will be installed to avoid plugging or collapse and to avoid erosion at the inlets and <br />outlets. Riprap will be installed as necessary to reduce the exit velocity. The minimum width will <br />be the width of the natural downstream channel. The riprap will be sized in the field based on the <br />"as -built" slope of the culvert and final configuration of the exit channel slope area. The sizing <br />shall be based on the Federal Highway Administration's HEC No. 11 "Use of Riprap for Bank <br />Protection" or other standard methods. All pipes will have a minimum cover of 12 inches. <br />Culverts and drainage ditches will be maintained periodically to prevent accumulation of debris <br />on the culverts inlets and outlets. <br />The following is an outline of the general design procedures used in the design of culverts: <br />Identify the need for a structure from topographic maps, and a visit to the site; <br />2. Determine the size and hydrology of the watershed in question; <br />3. Perform SEDCAD, or other acceptable software, computer run to determine the <br />peak runoff from a 10 -year, 24-hour precipitation event; <br />4. Using SEDCAD, or other acceptable software, computer run to determine the <br />proper size of culvert to handle the peak runoff from a 10 -year, 24 hour <br />precipitation event. SEDCAD design runs can be found in Appendix 2.05.3(3)-1 <br />Other applicable methods of culvert design include the use of charts developed by the Federal <br />Highway Administration, published in Hydrologic Engineering Circular HEC -5 (FHA, 1980), <br />and Hydrologic Design Series HDS-3 (FHA, 1980). <br />Charts published in HEC -10 (FHA, 1978) are also used; however, exit velocities must then be <br />determined by other methods. Headwater conditions are typically examined by using HEC -5 <br />Section 2.05.3(3) Page 8 Sept. 2015 (TR -11) <br />