Laserfiche WebLink
<br />Cross Section <br /> <br />The channel may be parabolic, "V" shaped or <br />trapezoidal.' The diversion is to be designed to have <br />stable side slopes. The side slopes for permanent diver- <br />sions should not be steeper than 3: I for maintenance <br />purposes and preferably 4: I. The back slope ofthe ridge <br />is not to be steeper than 3: land preferably 4: I. The <br />ridge after settlement is to be 4.0 feet at the design water <br />elevation. In determining the cross section on tempo- <br />rary diversions, consideration should be given to soil <br />type and frequency and type of equipment that is an- <br />ticipated to be crossing the diversion. In no case should <br />side slopes be steeper than I: I. <br />'See Exhibit 6for channel dimensions. Note that the <br />figures for Parabolic sections include an allowance for <br />freeboard. <br /> <br />Outlets <br /> <br />Diversions are to have adequate outlets which will con- <br />vey runoff without damaging erosion. The following <br />types of outlets are acceptable: <br /> <br />1. Natural or constructed vegetated outlets capable of <br />safely carrying the design discharge. The outlet <br />should be established and well vegetated prior to <br />construction of the diversion. <br /> <br />2. Properly designed and constructed grade stabiliza- <br />tion structures, tile outlets or storm sewers. <br /> <br />3. Open ditch channels which are stable and have <br />adequate capacity and depth. <br /> <br />4. A stable area having a good sod cover or a wood- <br />land area with a deep erosion resistant litter. When <br />one of these two types of outlets is used, the outlet <br />end of the diversion channel should be flared in a <br />manner to spread the water over a wide area at a <br />shallow depth. <br /> <br />Protection Against Sediment <br /> <br />Temporary diversions do not require protection from <br />sediment. <br /> <br />Permanent diversions shall have, as a minimum, a filter' <br />strip of vegetation maintained above the channel. <br />Where soil or climate preclude the size of such strips, <br />the design shall include extra capacity for sediment. <br /> <br />The diversion ridge and channel should be seeded to <br />perennial grass to prevent erosion. <br /> <br />Small eroded areas and sediment-producing channels <br />draining into the diversion should be shaped and seeded <br />prior to or at the time the diversion is constructed. <br /> <br />Construction <br /> <br />All trees, brush, stumps, and other objectionable ma- <br />terial must be removed so they will not interfere with <br />construction or proper functioning of the diversion. All <br />ditches or gullies which must be crossed should be filled <br />and compacted prior to or as part of the construction. <br />Fence rows and other obstructions that will interfere <br />with construction or the successful operation of the <br />diversion need to be modified or removed. <br /> <br />The base for the diversion ridge is prepared so that a <br />good bond is obtained between the original ground and <br />the placed fill. Vegetation is removed and the base <br />thoroughly scarified before placement of fill. <br /> <br />The minimum constructed cross section must meet the <br />design requirements. The top of the constructed ridge is <br />not to be lower than the design elevation plus. the <br />specified amount for settlement. <br /> <br />Fertilizing, seeding, and mulching must conform to the <br />recommendations in this handbook. <br /> <br />If there is no sediment protection provided on tempo- <br />rary diversions, it 'should be anticipated that periodic <br />cleanout may be required. <br /> <br />Construction operations must be carried out in such a <br />manner that erosion and air and water pollution are <br />minimized. State and local laws concerning pollution <br />abatement must be complied with. <br /> <br />42 <br />