Town Canal

The Town Diversion Dam and Canal are located on the left bank of the Yakima River at river km 259.5 [river mile 161.3], about 11 km (7 mi.) northwest of Ellensburg, Washington. Water is diverted from the Yakima River into the Town Canal. The carrying capacity of the canal is about 7 m3/sec (250 cfs). Canal flow varies from 2.8 to 7.0 m3/sec (100 to 250 cfs) and is regulated by four headgates about 75 m upstream of the Town Screens. The screening facility (Figure 1) diverts fish drawn into the canal and directs them back to the Yakima River. Trash racks, located between the headgates and screen array, "filter" out large debris that could damage the screens or interfere with flow control through the screening facility.

The screening facility houses ten rotary drum screens with axes parallel to the length of the structure. Each screen is about 3.7 m (12 ft) long and 1.7 m (5.5 ft) in diameter. Screen mesh openings are 3.2 mm (1/8 in.). Water depth in the forebay is maintained at about 1.3 m (4.2 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 and out the fish return pipe. Flow through the fish bypass is 0.6 m3/sec (20 cfs).

The drum screens are installed at a 26-degree angle to canal flow. This angle provides 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.


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