The Wapato Canal Fish Screening Facility (Wapato Screens) is located about 1 km downstream of the headgates of the Wapato Canal. The screening facility (Figure 1) diverts fish entering the canal and directs them back to the Yakima River.
The trash racks from the old screening facility, immediately upstream of the new Wapato Screens, are used to "filter" out debris entering the canal. The screening facility houses 15 rotary drum screens with axes parallel to the length of the structure. Each screen is about 7.3 m (24 ft) long and 4.6 m (15 ft) in diameter. Water depth at the screens varies with canal flow; however, the depth across the face of the screens at full canal level is normally about 3.7 m (12 ft).
The flow control structure and the separation chamber are located at the downstream end of the screen facility. Two fish bypass pipes and the terminal bypass, each with a flow of about 1.4 m3/s (50 cfs), feed into the separation chamber. During normal operation, about 4.2 m3/s (150 cfs) of water enter the separation chamber. About 0.9 m3/s (30 cfs) of water and all fish that are diverted in front of the screens pass through the flow control structure and out the fish return pipe. Two bypass water return pumps, each with a pumping capacity of 1.4 m3/s (50 cfs), are located behind traveling screens near the terminus of the separation chamber. The traveling screens are equipped with screen washers to prevent fish and debris from being entrained in the pumpback system.
The pumpback system is not used during normal operation. Adequate flows are maintained in the fish bypass by discharging 3.4 m3/s (120 cfs) of water back to the Yakima River over adjustable weirs in the pump basin. When the pumps are operating, flow over the weirs is reduced. Thus, bypass flows are achieved by adjusting weirs in each fish bypass (Gates 1, 2, and 3), the fish return (Gate 4), and the two weirs behind the pump intakes (Gates 5 and 6).
Figure 1. Flow Control Structure and Fish Bypass System in the Wapato Canal Fish Screening Facility