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DRAFT - FEBRUARY 9, 1990 <br /> <br />Be constructed according to the Nationwide Urban Runoff Program <br />(NURF) guidelines. <br /> <br />Have an outlet control structure that effectively prevents floating <br />debris and oils from entering the downstream conveyance system. <br /> <br />Control of Streambank Erosion and Streambed Degradation <br /> <br />Streambank erosion and streambed degradation control measures will: <br /> <br />Be employed on a case-by-case basis whenever the net sediment <br />transport for a reach of stream is greater than zero as the result <br />of development activities or whenever the stream's natural tendency <br />to form meanders directly threatens damage to structures, utilities <br />or natural amenities in public areas. <br /> <br />Include effective energy dissipation devices or stilling basins to <br />prevent streambank or channel erosion at all stormwater outfalls. <br />Specifically: <br /> <br />Outfalls with outlet velocities of less than 4 fps that <br />project flows downstream into the channel in a direction at <br />least 30 degrees from the normal flow direction generally <br />shall not require energy dissipators or stilling basins, but <br />they may need some riprap protection. <br /> <br />~Energydissipators shall be sized to provide an average outlet <br />velocity of no more than 6 fps. If riprap is also used, the <br />average outlet velocity may be increased to 8 fps. <br /> <br />Riprap stilling basins shall not be used where outlet <br />velocities exceed 8 fps. <br /> <br />2302047/LRRWMO.WP/TMK 7 <br /> <br /> <br />