Effects of Alpine hydropower dams on particle transport and lacustrine sedimentation

The effects of high-alpine hydropower damming on lacustrine sedimentation and transport of solid particles were investigated in the glaciated Grimsel area and in downstream Lake Brienz, providing quantitative denudation rates and sediment yield on a source-sink basis. A total of 271 kt/yr of solid particles entered the Grimsel reservoirs on average in the last 71 years, mostly by turbiditic underflows that focused sedimentation in depocenters upstream of obstacles such as bedrock ridges, submerged moraines, or dams. This is equivalent to a sediment yield of 2430 t/(km(2)yr) in the catchment (111.5 km(2)) or a denudation rate of 0.94 mm/yr. A total of 39 kt/yr of the fine fraction (