Modification of Fish Ladders, Bonneville Dam, Columbia River, Oregon and Washington: Hydraulic Model Investigation

Modifications of the flow control sections and counting stations of the Bradford Island and Washington Shore fish ladders at Bonneville Dam were necessary to accommodate rapid pool changes which will result from fluctuating discharges caused by power peaking at hydroelectric projects upstream. Fishway operation for the extreme flood control pool range from elev 70.0 to elev 82.5 (feet above mean sea level) was considered. The normal range for design was between elev 72.0 and 80.0. A portion of the forebay, the exit control section, the counting station, the supply channel for auxiliary water, and typical sections of each ladder were studied in a 1:14-scale model. Hydraulically satisfactory designs for automatic control systems with vertical-slot nonoverflow walls, bleed-off and add-in diffusers, auxiliary water supply, and moveable-board underwater counting station and for revised overflow weirs downstream were developed in the model. The designs for both ladders were operative with forebay levels between elev 70.0 and 76.5. Relatively simple modifications of those designs that could extend their range of operation to pool elev 80.0 were also developed. None of the plans was adequate at pool elev 82.5