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عمران::
angled screen
Ocean Bay/Estuary Intake technology On-shore Off-shore On-shore Off-shore Active screening technologies Adjustable vertical barriers x x x Angled screens x Center-flow/dual-flow screens x x Fish return conveyance systems x x x x Modular inclined screens x x x x Vertical traveling screens Standard through-flow vertical traveling screens x x Fine-mesh modified traveling screens x x x x Other modified traveling screens x x x Passive screening technologies Aquatic filter barriers x Barrier nets x x Light and acoustical deterrents x x x x Louvers x Narrow slot/wedgewire screens x x x x Porous dikes x x Velocity caps x x Variable frequency drive (VFD) pump seasonal/ diurnal flow management x x x x
Angled Screens.
Angled screen installations are composed of a series of vertical traveling screens arranged strategically at an angle to maximize diversion of fish and other marine animals to a primary bypass line� The organisms captured in the primary bypass line will typically be led to a secondary bypass line, holding tank, or released back to the natural habitat� Most angled screen installations have been added to protect young salmonids� Angled screens have been studied for possible use at intake structures to protect a variety of fish in freshwater, riverine, estuarine, and marine environments (Electric Power Research Institute [EPRI] 1999)� They also have been used in hydroelectric and irrigation intake facilities� Installations of angled screens in combination with diversion and fish return systems are effective at removing entrapped and/or impinged organisms with varying degrees of return survival� It can protect the young-of-the-year and older fish, and is an effective device for preventing impingement� The combined experience gained from past stud- ies indicates that angled screen systems can be very effective for diverting fish into a bypass line if given the proper physical and hydraulic conditions� There have been various studies on angled screen performance at different facilities around the U�S�
At Brayton Point Station Unit 4 in Mt� Hope Bay, Massachusetts, an 18-month biological effectiveness evaluation was conducted to determine the species type, number and initial/extended survival life of fish diverted in the bypass line (Davis et al� 1988)� This intake structure has eight openings that extend to the bottom of a skimmer wall� There are trash racks at the inlet and behind this is a screenwell� A center wall divides the structure into two halves� Each half is equipped with three flush-mounted vertical traveling screens set 25 normal to the flow� The fish are guided to a rectangular opening and are then sluiced back to Lee River� The diversion efficiency of the angled screen was determined by the comparison of the proportion of fish entering the bypass to the num- ber of fish entering the screenwell� The number of fish that entered the screenwell was calculated by adding the fish impinged on the angled screens to the estimated number of fish diverted during the impingement period� The survival rates at the Brayton facility varied from 25 percent for frag- ile species to 65 percent for hardy species� The overall diversion efficiency of all species was 76�3 percent (Davis et al� 1988)� The study noted that the diversion efficiency increased to 89�7 percent when young-of-the-year bay anchovy were excluded� In sum, there were a total of 79,206 fish col- lected from the angled screens and diversion flow during the experimental period and the system was not very effective for young bay anchovy but was sufficient to adequately protect the other species�
A full-scale experiment was conducted in the Danskammer Point Generating Station on the Hudson River in 1981 (EPRI 1999)� The angled screen system was installed in a cooling water intake canal� The configuration of the system consisted of two vertical traveling screens set at an angle 25° to the direction of flow� The angled channel led to a 0�5-ft (15-cm) -wide bypass line� This line then connected to fish collection and larval collection tanks� The diversion effectiveness study was conducted over a three-year period, and divided into two sections: a study of young/ older fish, and a study of ichthyoplankton (EPRI 1999)� Both the young and older fish were col- lected on a seasonal basis from the fish pump discharge using nets and from the collection tanks for which the fish has a 96-hour mortality expectancy� A total of 59,309 fish comprised of 38 spe- cies were collected from February 18, 1981 to October 27, 1983� The diversion efficiency ranged from 95�4 to 100 percent with a mean of 99�4 percent� The species affected on the river were the bay anchovy, blueback herring, white perch, spottail shiner, alewife, Atlantic tomcod, pumpkin- seed, and American shad� The study determined that the overall efficiency (diversion efficiency ×
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