Dryden Screening Facility

The Wenatchee Reclamation District Canal begins at Dryden Dam on the left bank of the Wenatchee River, River Mile 16.1 (River Kilometer 25.9). The Dryden Fish Screening Facility (Dryden Screens) is located about 500 ft downstream of the Dryden Dam (Figures 1 and 2). The screening facility, completed in the spring of 1993, replaced an old rotary drum screening facility. The canal was originally built to carry 1,500 cubic ft per second (cfs) of water which was used for both irrigation and power generation. However, power generation has ceased and the canal is now used for irrigation and to provide water for fish rearing ponds.

The new screening facility is designed for a maximum flow of 230 cfs. It consists of seven fixed plate vertical profile bar panels installed at a 15 angle to canal flow. The openings in the profile bar are 0.125 in. (3.17 mm) wide. Each panel is 13 ft wide with a submergence of 6.4 ft at maximum canal level, for a total submerged screening area of 582 ft2. Using the Washington State screening requirement approach velocity of 0.4 ft per second and assuming even distribution of water through all areas of the seven panels, the facility should effectively screen 233 cfs of water. Canal flow is regulated by a manual headgate structure about 500 ft upstream of the screens. Withdrawal from the canal is estimated by headgate opening and by reading a staff gage in the screen forebay. To ensure balanced flow among the screen panels, adjustable vertical louvers (for porosity control) are installed behind each screen. The screening surface is cleaned with an electric power-driven nylon brush that travels along the face of the screens at regular intervals.

Fish bypass flow of 20 cfs is achieved by adjusting a 36-in. wide weir gate mounted on top of a 4-foot high ramp in the entrance to the bypass slot. Flow through the bypass is maintained by adjusting the bypass weir gate relative to the canal water surface. A fisheries evaluation area 4 ft wide by 16 ft long is built into the fish bypass slot. The fish return has three major components:


Figure 1. Location of Dryden Dam and the Dryden Fish Screening Facility




Figure 2. Flow Control Structure and Fish Bypass System in the Dryden Fish Screening Facility