Toppenish Creek

Water is diverted from Toppenish Creek into the Toppenish Creek Canal about 8.3 km (5 mi) south of White Swan, Washington. Carrying capacity of the Toppenish Creek Canal is about 1.7 m3/s [60 cubic feet per second (cfs)]. Canal flow varies from 0.3 to 1.7 m3/s (10 to 60 cfs) seasonally and is regulated at the canal head gates about 75 m (246 ft) upstream of the Toppenish Screens. The screening facility (Figure 1) diverts fish that enter the canal and directs them back to Toppenish Creek. Trash racks placed in the canal about 10 m (33 ft) upstream of the screening facility "filter" out large debris that could damage the screens or interfere with flow control through the screen facility.

The screening facility houses three rotary-drum screens with axes parallel to the length of the structure (Figure 1). Each screen is about 4 m (12 ft) wide and 1.8 m (6 ft) in diameter. Screen mesh openings are 3.18 mm (1/8 in.). Water depth at the screens varies with canal flow. The average water depth across the face of the screens is about 1 m (3 ft).

The rotary screens are installed at an angle of 26 degrees to canal flow. This orientation provides a ratio of sweeping velocity to approach velocity equal to or exceeding 2:1. Maximum-allowable approach velocity is 0.15 m/s (0.5 f/s). Screen orientation and flow-velocity differential help direct fish to the fish return pipe and back to the creek.

Figure 1. Flow Control Structure and Fish Bypass System in the Toppenish Creek Canal Fish Screening Facility