Replacing Low Head Dams with Nature-like Fishways to Improve Fish Passage

Year: 2020
Presenter/s: Matthew Prociv
Symposium Session: 2020 - 11 Dam removal in the Pacific Northwest
Topics covered: beavers, fish passage, hydraulics, instream structure (culvert/bridge/dam), stream, and urban


Impoundment structures, such as dams, are a reliable method to divert water from otherwise naturally flowing water courses to other locations and consumptive uses, but are also impediments or full barriers to fish passage and alter the natural habitat and hydraulic and sediment conveyance characteristics of the water courses. Several projects, currently in various stages of implementation, from in design to constructed and operating, are attempting to improve/restore fish passage by returning rivers to more nature-like channels while maintaining reliable water supplies. In this presentation we will examine the needs driving these projects, the physical improvements to the rivers, infrastructure, and affected environment, and the potential pitfalls involved in the replacement of impoundment structures with regraded, stabilized, nature-like channels while simultaneously maintaining or expanding water supply diversions. We will also explore the geomorphic and hydraulic characteristics that make impoundment structures good candidates for replacement with regraded channels; discuss how fish and lamprey run timing and biomechanics are incorporated into design of the regraded channels to make them successful; examine how natural hydraulic and sediment conveyance processes of the water course may be restored; and discuss management related considerations such as risk, uncertainty, maintenance, and costs.