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عمران::
intake screen
The withdrawal of seawater affects the biological resources of the source water body through two processes: impingement and entrainment� Impingement refers to biota, typically fish, becoming physically trapped on the intake screens� Entrainment refers to biota getting drawn into the intake with the seawater inflow� Impingement and entrainment mortality associated with the operation of open intake systems has historically been one of the drivers behind the use of intake wells and infiltration galleries�
A number of facilities employ intake systems that collect fish and other organisms removed by intake screens and return them to the source water� The effectiveness of such systems to return the organisms is relatively easy to measure, but the survival and ecological success of the returned organisms is difficult to observe or quantify� It is a commonplace occurrence for the return point to become a fish feeding station for larger fish and birds� Generally, the best practice is to use intake locations and designs that avoid entrapping fish, such as shoreline locations rather than on dead- end channels or sloughs, and to use louvers and passive screens such as narrow-slot low-velocity screens to allow organisms to be swept away from the intake area�
A number of seawater intake facilities have significantly reduced the biofouling of both intake screens and system conduits through the use of antifouling coatings� Though the antifouling coatings materials and application methods are still experimental, they have proven effective in their earlier stages of service�
Both pump-augmented and gravity-flow return systems have the advantage of minimizing recirculation and re-impingement of debris and organisms on intake screens due to their relatively large transport distance capability, but pump-augmented systems often result in mechanical abra- sion and high organism mortality� The gravity sluiceway return system reduces mechanical abra- sion, but may result in a higher rate of re-impingement due to the relatively limited transport distances� Returned fish would be susceptible to disease and predation at the fish return discharge point due the stress of passage through the pumped fish return system�
intake screens on the shoreline� The vertical traveling screen system configuration consists of large vertical meshed screen panels (commonly 3⁄8-in�, or 10-mm opening) mounted on two parallel chains and motor operated from the upper sprocket� Figure 2�9 shows a conventional vertical trav- eling screen� The screen rotates periodically for cleaning with a direct spray nozzle; the debris is collected in a trough and carried to a refuse basin�
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