The impact of run-of-river dams on sediment longitudinal connectivity and downstream channel equilibrium

F. J. Magilligan, M. O'Brien, M. Marti, C. E. Renshaw

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Dams disrupt the natural downstream sediment flux frequently contributing to degraded downstream channels. Previous research has addressed the geomorphic impacts below larger dams that simultaneously regulate flow and trap sediment, with minimal attention addressing smaller run-of-river (RoR) dams that do not significantly affect hydraulic residence times but with unknown impacts on sediment flux and channel equilibrium. We examine five RoR dams that range in height from 1.5 - 12 m draining watersheds of 12 - 447 km2. To capture the role of RoR dams on sediment flux we measured the impacts on both suspended load and bedload and on resulting downstream channel morphology. To quantify bedload transport and potential sediment trapping, we emplaced RFID pit tags in 800 clasts ranging in size from 15 - 81 mm which were subsequently monitored using a backpack antennae coordinated with a handheld GPS to capture clast location. To monitor suspended sediment transport, four INW Aquistar Turbo turbidity meters were installed in and below the reservoir at two sites. Longitudinal profiles and channel cross-sections were measured at control sites above/in/below the reservoir along with Wolman pebble counts. 419 rocks moved during the one year sampling period, and 275 clasts were displaced over the dam - 204 of which spent some time in the reservoir. Using the critical Shields parameter to represent equilibrium, downstream reaches, although different in morphology and bed sedimentology compared to control reaches, have maintained equilibrium following dam emplacement in part reflecting the minimal sediment trapping of suspended load and bedload.
Original languageEnglish (US)
Title of host publicationAGU Fall Meeting Abstracts
StatePublished - 2018


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