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<br />STANDARD CULVERT OUTLET TREATMENT <br /> <br />Standard practice is to use the same treatment at the culvert <br />entrance and exit. It is important to recognize that the <br />inlet is designed to improve culvert capacity or reduce <br />headloss while the outlet structure should provide a smooth <br />flow transition back to the natural channel or into an energy <br />dissipator. Outlet structures should provide uniform <br />redistribution or spreading of the flow without excessive <br />separation and turbulence. It may not be possible to satisfy <br />both inlet and outlet requirements with the same end treatment <br />or design. As will be illustrated in chapter IV, properly <br />designed outlet structures are essential for efficient energy <br />dissipator design; and in some cases, may substantially reduce <br />or eliminate the need for other end treatments. <br /> <br />II-C - RIPRAP PROTECTION <br /> <br />Some energy dissipators provide exit conditions, velocity <br />and depth, near critical. This flow condition rapidly adjusts <br />to the downstream or natural channel regime; however, critical <br />velocity may be sufficient to cause erosion problems requiring <br />protection adjacent to the basin exit. <br /> <br />Figure II-C-l provides the rip rap size recommended for use <br />downstream of energy dissipators. The length of protection <br />can be judged based on the magnitude of the exit velocity <br />compared with the natural channel velocity. The greater <br />this difference, the longer will be the length required for <br />the exit flow to adjust to the natural channel condition. <br />A filter blanket should also be provided, see reference <br />II-C-l. <br /> <br />II-S <br />