Abstract
The ecological effects of sediment flushings from artificial reservoirs have been widely documented, but the underlying sedimentdynamics are less well known. We investigated sediment dynamics associated with a long flushing event divided into two peri-ods (2 and 1 week) in an Alpine river, each followed by a clear water release (‘washing’) from the reservoir. Suspended sedimentdynamics were investigated at the event and annual time scale, and at the river segment (~1000 channel widths) and reach (~100channel widths or less) spatial scales. Analysis of suspended sediment concentration (SSC) and streamflow time series from 5in situ calibrated optical turbidity sensors reveals a downstream decrease in the total passing sediment fluxes, a spatial trendthat is paralleled by the theoretical suspended sediment transport capacity, allowing for the estimation of the deposited finesediment volume in different reaches. Washing events result in variable effects among reaches, with some experiencing net sed-iment entrainment and others net deposition. Out of 16 quantified sediment fluxes, 5 were statistically significant with p < 0.05,with an average uncertainty of 23% in fine sediment flux quantification. Georeferenced analysis of coloured gravel-cobble plotsbefore and after the two flushing events revealed partial reach-scale mobility of the coarse bed surface material, particularly inthe geomorphic units located at lower elevations and more exposed to higher flows (edges of side bars nearby riffles or rapids),while local fine sediment deposition was observed at less exposed units, such as side channels or point bars in river bends. Grainsize distributions of surface sediment taken in the same locations before and 1 month after the flushing reveal a clear shift to-wards a finer sediment composition, which is partially retrieved also 1 year after the event. Event-averaged SSC values duringthe flushing are considerably higher compared to natural flood events in such a regulated river, with SSC-streamflow relationsbeing highly irregular and event-dependent, especially during the flushing. The work shows the relevance of multi-scale (timeand space) investigation of sediment dynamics for planning and monitoring sediment flushing from artificial reservoirs.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,provided the original work is properly cited.© 2025 The Author(s). Hydrological Processes published by John Wiley & Sons Ltd.