Solutions for Improving Fish Passage and Public Safety at Low Head Dams

During the 19th and 20th centuries, many low-head dams were constructed on rivers for water supply, ice harvesting, recreation, navigation, power generation (mills), and flow measurement. Due to the knowledge base at the time, little consideration was given to fish passage and public safety when most of these structures were designed and constructed. With significant development occurring in the vicinity of these structures, growing interest in water-based recreation, and the recent movement to restore river and stream environments to a more natural condition, many of these dams are now subject to intense pressures for their removal. When it is necessary to keep the structure in service, the dam owner is often faced with the difficult problems of addressing public safety concerns and providing effective fish passage. This paper presents the authors’ experience rehabilitating low head dams to improve public safety and provide effective fish passage. Lessons learned from experience with litigation related to drownings at low head dams are discussed with an emphasis on design concepts for modifying low head dams to eliminate the hazardous hydraulic roller. State-of-the-art designs for fish passage facilities for low-head dams will also be presented including Denil, Vertical-Slot, Pool and Weir, Rock Ramp and Nature-Like fishways. The recent rehabilitation of several low-head dams are presented as examples. In addition to providing fish passage, the design of these dams included modern features to eliminate the hazardous hydraulic roller and improve public safety. 20 pp, 22 references.