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14-6 <br />* Outlet Control Zone - The purpose of this zone is to control <br />the level in and rate of discharge from the SB. In addition, <br />the outlet must provide a smooth transition of flow from the <br />settling zone, including holding velocities to values that will <br />not disturb solids in the storage zone. Velocity control might <br />be accomplished with a submerged weir or berm, baffles, or with <br />a silt fence. A means of trapping buoyant debris and <br />preventing it from being carried downstream should also be <br />included in the outlet control zone. <br />Finally, the outlet control zone should be hydrologically and <br />structurally designed to accomodate, without failure, flood flows well <br />in excess of those used to design the settling function. For this <br />reason, an emergency spillway is normally included as part of the a~tlet <br />control zone. Various combinations of weirs, pipes, drop inlets, <br />service spillways, emergency spillways, and infiltration area:: are <br />typically used to form the outlet control zone. The types and sizcs of <br />these units are a function of the SB design criteria and flood flow <br />design criteria. <br />The design of a SB, excluding structural and geotechn'ical <br />considerations, may be viewed as consisting of the following nine step <br />process: ~ <br />1) Collect and analyze watershed data. <br />