Hydraulic and geomorphological effects of run-of-river dams

The practice of dam removal has received increasing attention as a consequence of maintenance and liability concerns related to the advanced age of many of these structures. Most dams that have been removed thus far are small run-of-river structures. As the number of removals of run-of-river dams increases, it is crucial to understand the effects that these structures have on river geomorphology and sedimentology while in place and how rivers respond to removals so that possible responses to future removals can be anticipated and predicted. This paper reviews current knowledge related to the influence of run-of-river dams on the hydraulics and geomorphology of rivers and suggests types of studies that need to be undertaken to address gaps in current knowledge. Compared to studies of large impoundment dams, field investigations of channel morphology and sedimentology upstream and downstream of run-of-river dams are few and limited in geographic scope. Available studies indicate that the response of rivers to the long-term existence of run-of-river dams is variable both in terms of upstream sediment storage and downstream channel erosion. Future research should focus on how geomorphological responses of rivers to run-of-river dams vary with geographical context and on integration of process-based field studies, numerical modeling and experimental investigations to determine the influence of these dams on flow structure, sediment transport, and patterns of channel erosion and deposition.