Determining Erosion Rates and Processes in the Pro-Glacial Area over a 28-Year Period

Abstract:

Glacially fed hydropower reservoirs in the Swiss Alps have experienced substantial increases in sedimentation recently. This sedimenation causes reduced reservoir capacity, turbine abrasion and increased need for sediment flushing, all of which reduce the eciency and economic viability of hydropower in the region. Although the issue is largely attributed to regional glacier retreat, there is a need for greater understanding of the specic processes that contribute to the increased sedimentation.

To evaluate these processes, we examine the Griesgletscher catchment, which lies in the central Swiss Alps and its runoff feeds a hydropower reservoir. The recent exposure of the glacier's fore-field (roughly 1986) due to the glacier's retreat beyond the reservoir's margin, along with its simple catchment area make it an ideal location to examine pro-glacial erosion. Here we present a time-series from 1986 to 2014 of digital elevation models (DEM) created from aerial photographs of the Griesgletscher's fore-field from each year except for 2. Comparison of DEMs from subsequent years yields erosion volumes and sediment balance over the 28 year period for the pro-glacial area. Bathymetry of the pro-glacial reservoir for select years allows us to speculate if the erosion of the recently exposed glacier fore-field is the sole source of sediment to the reservoir, or if alternative processes such as increased glacial erosion or mobilization of sub-glacial sediments could contribute. We correlate erosion amounts with runoff volumes from the Griesgletscher and changes in the the glacier's morophology and coverage. Additionally, implimentation of the Glacier Evolution Runoff Model allows us to examine the variability in the glacier's runoff on the hourly to daily scale. By examining these relationships we constrain the processes contributing to the erosion of the Griesgletscher's pro-glacial area.