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' Silt fence may be used for areas where sediment control is needed for intermediate periods of ' time (i.e., more than a year but not permanently). Silt fences will be placed on the down gradient side of the disturbed area (Figure D-1 and Figure D-2). To the extent possible, silt fence will be installed on the contour. However, silt fences are ideal for installation along perimeters that vary in contour when flow and sediment volumes are low. Care must be taken ' to avoid directing any excessive amounts of flow to low points which may overload fence capacity and result in fence failure. Support systems for silt fence will be adequate to ' be keyed into the ground according to standard installation procedures. Silt fences will not be used where excessively rocky sods prevent their proper installation. Silt fences will be routinely inspected and maintained following significant runoff events. The cost of ' maintainurg silt fence vs. the cost of implementing more costly control measures will be taken into consideration when determining which control measure to use. Silt fence may also be used as a substitute for straw or hay bale check dams, since its effective life is usually longer. ' di S t T e men raps Sediment traps ate small incised dugouts or depressions that may be placed interntittently along ' or aY the outlet of a water course or erosion feature (Figure D-3). They are effective in ponding surface water, increasing the time of concentration, reducing peak flows and gapping sediments. Care should be taken at the inlet to ensure a gradual or moderate slope into the ' pool. Creating a steep angled drop into the pool may cause headcutting upstream and sloughing or accelerated erosion which can significantly decrease the holding capacity of the structure. In locations where or during periods of time when erosion rates and sedimentation are high, sediment traps must be maintained frequently. Use, placement, functional life ' expectancy and ability to perforn maintenance should be considered when using sediment traps. ' For small impoundments where human safety and health risks are not of concern, generic designs that are modified to take into account local site conditions may be utilized for non- critical structures. ' Sedimentation Basins ' A number of good resources ate available for the design, sizing and construction procedures of sedimentation basins, including SEDCAD University of Kentucky at Lexington (SIDCAD 4.0, 1998), the SCS National Engineering Handbook Section 19 (SCS, 1985), Earth Manual ' (Department of the Interior, Bureau of Reclamation, 1974), and the SCS Engineering Field Manual (SCS 1984). A professional engineer familiar with sedimentation ponds will be utilized in site specific designs for sedimentation basins or other large impoundments that present risks to the environment or to public health and safety or that are used for final water ' treatment purposes. A professional engineers certification is normally required by regulation for sedimentation basin and other lazge impoundment designs. ' Sedimentation basins primarily serve to trap sediments. Secondarily they reduce or abate water pollution by providing a collection structure for the storage of chemical contaminants, debris and other processing wastes. The designs of dams, spillways and drainage facilities should be in accordance with standard engineering principles appropriate for the class and kind of ' structure being considered. Dewatering devices should be incorporated where permanent pools are unacceptable or where adequate containment volumes for runoff must be provided. withstand the antic~'pated flow volumes and sediment loads anticipated for the installation area. Sediment fence wilt be UV resistant with fabric-tensioning strips. The bottom of the fabric will ' Ill