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<br />1 Typical Advantages <br />• Positive seals are easier to make with fixed or pneumatic seals <br />• Minimal seal maintenance is required <br />• Vertical plate screens can handle a large range of flows and fluctuations in forebay elevation <br />• The only demonstrated technique to screen down to egg size life forms at high flow rates <br />Typical Disadvantages <br />• Velocity variability across the screen as flow spatially varies <br />• Debris accumulation must be removed mechanically, except for the flat plate screen where <br />debris is flushed off the end of the screen and must be handled for disposal <br />• Velocity hot spots may develop requiring the use of guide vanes <br />• Protection from icing needed in cold climates <br />Application to Limiting Downstream Passage. Fixed plate screens are not particularly applicable <br />to limiting downstream passage from reservoirs. Normally reservoirs have a greater than 10-foot <br />water depth approaching the dam, and shallower forebay areas tend to be limited in area and have <br />' high velocities. Outdoor screens in colder climates are subject to icing and frequent clogging by <br />small debris. <br /> <br />F <br /> <br /> <br />1 <br />1 <br /> <br /> <br />Control Structure Feasibility Evaluation <br />1 Miller Ecological Consultants, Inc., February 18, 1997 <br />1-19