Adult Fish Ladders

Operations    Wells Reservoir    Map of Project    Juvenile Bypass System    Adult Fish Ladders    Hatcheries & Acclimation Ponds    Recreation    Wildlife Resources

Wells Dam has two adult fish ladders, one on each side of the dam immediately adjacent to the right and left banks of the Columbia River. The ladders were built during the original construction of the dam. Each ladder contains 73 fishway weirs. They descend one foot per pool and discharge a constant 48 cubic feet per second of river flow through the ladder. This discharge flows from one pool to another over the walls and through submerged orifices. Depending on the tailwater elevation, fish can swim over many of the lower weir walls without the need to pass through the orifices. The upper 17 pools hold more water, have larger orifices and are used to control the amount of water flowing through the lower sections of the ladder.

Each of the two fish ladders has a single entrance for fish, which is located at the bottom of each ladder’s collection gallery. Each entrance opens into a collection gallery that is flooded with water in excess of that flowing in the fish ladders. This excess “attraction water” is designed to attract migrating fish into the collection gallery and ultimately into the fish ladder. As fish move up the ladders, provisions for sorting and trapping fish are located adjacent to Pool 40. This area is equipped with a holding box and adult Passive Integrated Transponder (PIT) tag detectors. In addition, the traps are also equipped with slide gates to either retain fish or return them to the ladder. This area is used for brood stock collection, for fish tagging and for other research opportunities. Pool 64 contains facilities for fish counting, including a viewing window, video cameras and a light panel. Pools 67 and 68 are equipped with PIT tag detection devices that interrogates each fish for a PIT tag and, once detected, will record the presence of each tag as the fish ascend the ladders.

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