Figure 1. Flow Control Structure and Fish Bypass System in the Westside Ditch Canal Fish Screening Facility
The screening facility houses four rotary drum screens with axes parallel to the length of the structure. Each screen is about 3.7 m (12 ft) long and 1.8 m (6 ft) in diameter. Screen mesh openings are 3.2 mm (1/8 in.). Water depth at the screens is maintained at about 1.6 m (5 ft). The fish bypass is located in the flow control structure at the downstream end of the screening facility. Water and fish diverted past the front of the screens pass through the fish bypass slot and out the fish return pipe. Flow through the fish return is 0.6 m3/s (20 cfs). A waste water channel is installed along the forebay wall opposite the drum screens to prevent flooding and canal bank erosion. No water flows out the waste water channel at normal canal forebay level.
The rotary screens are installed at an angle of 26° to canal flow. This orientation is designed to provide a sweeping-velocity-to-approach-velocity ratio equal to or exceeding 2:1. The maximum allowable approach velocity is 0.15 m/s (0.5 fps). Screen orientation and flow velocity differential help direct fish to the fish return pipe and back to the river.