Canal flow is regulated at the canal headgates about 1 km upstream of the Richland Screens. The screening facility diverts fish that have entered the canal and directs them back to the Yakima River. Trash racks placed in the canal upstream of the screening facility (Figures 2 and 3) "filter" out large debris that could damage the screens or interfere with flow control through the screen facility.
Figure 1. Yakima River Basin Showing Location of the Richland Canal Fish Screening Facility and the Wapato Canal Fish Screening Facility
Figure 2. Flow Control Structure and Fish Bypass System in the Richland Canal Fish Screening Facility
A wastewater channel is immediately upstream of the trash racks. The channel runs perpendicular to the canal and discharges into the Yakima River. Excess water spills into the wastewater channel when the canal flow exceeds the combined flows through the screens and fish return pipe. Wastewater flow can be regulated to help keep debris from accumulating on the trash racks, but its primary function is to prevent flooding of the screening facility during the winter when ice forms at the screens.
The screening facility houses four rotary drum screens (Figure 2) with axes parallel to the length of the structure. Each screen is about 3 m (10 ft) wide and 1.7 m (5.5 ft) in diameter. Screen mesh openings are 3.18 mm (1/8 in.). Water depth at the screens varies with canal flow. However, the average depth across the face of the screens is about 1.7 m. The screens are mounted on top of a 0.5-m curb on the forebay floor, so that the water surface is normally about 0.5 m below the crest of the screens.
The fish bypass is located in the flow control structure at the downstream end of the screening facility (Figure 2). 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 adjusted to about 0.7 m3/sec (25 cfs) by stoplogging "Slot C".
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/sec (0.5 fps). Screen orientation and flow velocity differential help direct fish to the fish return pipe and back to the river.