1I2: Low Stress Fish Passage: An Innovative Approach For Medium and High Head Dams
July 13, 2022
Water and Environment (including Social Issues)
The environmental acceptability of many existing and proposed medium and high head dams hinges on the ability to provide safe and economic passage of both upstream and downstream migrating fish. In some cases, the only available space includes areas subject to flood born debris damage, erosion, or sedimentation. The system developed by Whooshh™ Innovations is successful in transporting fish of uniform size over dams. Trap and truck operations have been successful but are expensive to operate. Mechanical fish lifts have worked where site geometry allows for a straight vertical or inclined lift of a tank. The proposed Obermeyer system combines pneumatically operated fish traps with a reversible pump-turbine for gently raising and lowering the water column in an auxiliary penstock between tailwater and headwater. Upstream migrating fish begin their ride by being drained from a fish trap at tailwater elevation down into a penstock. A water-propelled crowder keeps them away from the pump-turbine and at the top of the water column, which remains at atmospheric pressure during transit between tailwater and headwater elevations and vice versa. This fish trap and auxiliary penstock may be designed into a new dam or retrofitted to an existing dam. Alternatively, the fish trap can be installed in conjunction with an existing but repurposed penstock. As with conventional hydroelectric penstocks, the penstock is configured to fit site conditions. The penstock may be surface mounted, suspended, embedded, submerged, or installed underground, for example. This flexibility and minimal footprint are in sharp contrast to fish ladders, for which space is not available on many sites, especially in the case of narrow canyons and steep terrain. Fish ladders are also limited in elevation change by the physical endurance limits of the fish. The Obermeyer system only requires the fish to enter the trap for them to catch an "elevator ride" over the dam. Fish are not subject to high-velocity flow, harmful pressure changes, or turbine transit. The pumping energy required for upstream transport is almost completely recovered while draining the penstock, which can be used for downstream as well as upstream fish passage. Energy use may be further halved by using two penstocks that are alternately filled and emptied by the pump-turbine located at the lower end of the penstocks. The pump-turbine associated with the fish passage system may also be used for increased and efficient hydropower generation during non-fish passage seasons. For downstream fish transport, fish may be trapped downstream of a headwater-elevation-tracking Obermeyer gate, and then periodically drained with their surrounding water into the penstock just upstream of the crowder. The fish and their supporting water column are then lowered down the penstock at speeds controlled by the reversible pump-turbine. As the water in the penstock drains, the reversible pump-turbine recovers almost all the energy used for pumping. The system may be adapted to low head fish passage, where the small footprint and ability to pass a variety of species efficiently is advantageous. For low head sites, energy recovery is of less consequence, and the reversible pump-turbine(s) are omitted. Upstream migrating fish are first trapped upstream of an Obermeyer gate. The water in the trap, along with the fish, is dropped into a sump below the tailwater level. No particular behavior of the fish is required – the fish and their surrounding water are moved by gravity. Water stored in a tank above headwater is flushed through a siphon, carrying fish from the sump below the fish trap to the headwater. Downstream passage would generally not need to be incorporated into such a system because downstream passage at low head facilities can readily be accomplished with a combination of open channel chutes and fish friendly turbines.