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Meltwater discharge from mountainous catchments
The research unit Mountain Hydrology and Torrents investigates hydrological processes in mountainous catchments. In an alpine environment, snow constitutes an important buffer of winter precipitation, which is released months later during snowmelt in spring. Understanding the discharge dynamics from mountainous catchments is important to assess the risks related to flooding, debris flow and sediment transport. The Snow Hydrology Research Group is particularly interested in the dynamics of snow water resources and subsequent meltwater generation from snow-dominated catchments – e.g. with respect to predicting snowmelt related flooding in spring, or to climate change effects on hydropower production.
The river Albertibach above Davos is a typical mountain stream, which constitutes a significant risk to subjacent settlement areas. These risks have already been counteracted with elaborate control structures in the riverbed. Its proximity to the SLF and existing measuring infrastructure from other SLF research projects in the headwaters of Albertibach made this particular stream an excellent subject for a study on meltwater generation. Starting in autumn 2008, an automatic gaging station has been build just above the tree line at Lochalp. The station complements infrastructure at the research site Wannengrat, mainly established thanks to the project Swiss-Experiment.
Continuous runoff data are typically deduced from stage measurements, a technique also used at Albertibach. Manual runoff measurements at different stage levels are required to convert stage data into discharge. This method, however, is inaccurate if the riverbed changes its profile over time. Therefore, the profile of the Albertibach was fixated at the runoff gage (see image). The stage is picked up by an ultrasonic range sensor as well as by a pressure probe in the measuring channel. The gaging station adds to the ongoing intensive investigations of the snowcover in the Wannengrat area.
Snow measurements using remote sensing techniques
In addition to automatic snow measuring stations and a wealth of manual measurement campaigns, the spatiotemporal distribution of snow is also determined with the help of a laser scanner. The laser scanner is positioned at various points in the catchment area and can survey the snow cover with an accuracy of about 5 cm. During the melting phase, weekly laser measurement campaigns are carried out to precisely follow the development of the snow cover.
At the Wannengrat site, we also tested a new optical scanner (Leica ADS80), which was flown over the site onboard a small aircraft. Thanks to scans from different angles, we determined the snow distribution over large areas and with high spatial resolution. The SLF also verified the snow depth mapping of the Leica ADS80 with manual measurements on the ground and with laser scanning data. Data gathered by the ADS80 is used to initialize models for large river basins and thus to improve the runoff forecast for larger basins.
Measurements from both the laser scanner and the ADS80 helped us develop a new stochastic model of the snow cover. This allows reproducing snow distribution over the course of the winter using data from a number of weather stations. Such models can also calculate the meltwater of the entire catchment. Therefore, data that are measured at the Albertibach will ultimately serve to develop models that could be used in operational risk prevention.