Hydrologie sous glaciaire
Sediment exported from partially glacierized alpine catchments has diverse impacts on the downstream reaches of mountain streams. It fills water storage dams and hydropower intakes and it may affect the morphology and ecology of mountain streams and river valleys (Gabbud & Lane, 2016).
This project aims at determining the structure and dynamics of the subglacial hydrological network of an alpine temperate glacier with the help of Ground Penetrating Radar (GPR), channel exploration and hydraulic modelling. The objective is to observe the structure of subglacial channels, to investigate their erosion into sediment, to observe their temporal evolution and to determine the rate of sediment erosion and transport on a sub-daily timescale. We attempt to demonstrate the development of fast-flowing subglacial channels over the course of a melt season (Nienow et al., 1998), and to show the erosion of these channels into sediment.
The main field site is the 'Glacier d'Otemma' in the South West of the Swiss Alps (at 2450 - 3800 m.a.s.l). This glacier has retreated by 2 km since 1964. Its length is of 8 km, the Equilibrium Line Altitude is situated at approximately 3000 m and the ice thickness reaches 260 m (Gabbi et al., 2012). The meltwater flows into the Mauvoisin hydropower lake, with a water intake operated by the company 'Forces Motrices de Mauvoisin'.
GPR survey grids on the glacier are repeated over the course of an ablation season in order to detect the location and size of channels. Mapping of one subglacial channel with a laser scanner (Mankoff et al., 2017) will serve as ground truth for the GPR surveys and provide high-resolution geometry as a boundary condition for a Large Eddy Simulation (Lane et al., 2004) of water flow inside the conduit. Methods to assess meltrate and glacier surface movement include LiDAR surveys, UAV photogrammetric imagery and timelapse photography. Meteo data is used to quantify the influence of variables such as temperature and precipitation on discharge and sediment transport.