Abstract
Abstract. The glacier-dammed Lac des Faverges, located on Glacier de la Plaine Morte (Swiss Alps), has drained annually as a glacier lake outburst flood since 2011. In 2018, the lake volume reached more than 2 × 106 m3, and the resulting flood caused damage to the infrastructure downstream. In 2019, a supraglacial channel was dug to artificially initiate a surface lake drainage, thus limiting the lake water volume and the corresponding hazard. The peak in lake discharge was successfully reduced by over 90 % compared to 2018. We conducted extensive field measurements of the lake-channel system during the 48 d drainage event of 2019 to characterize its hydraulics and thermodynamics. The derived Darcy–Weisbach friction factor, which characterizes the water flow resistance in the channel, ranges from 0.17 to 0.48. This broad range emphasizes the factor's variability and questions the choice of a constant friction factor in glacio-hydrological models. For the Nusselt number, which relates the channel-wall melt to the water temperature, we show that the classic, empirical Dittus–Boelter equation with the standard coefficients does not adequately represent our measurements, and we propose a suitable pair of coefficients to fit our observations. This hints at the need to continue research into how heat transfer at the ice–water interface is described in the context of glacial hydraulics.
Highlights
Glacier-dammed lakes are often unstable as ice dams are prone to rapidly fail, which leads to partial or total drainage of the impounded lake through supraglacial, englacial and subglacial conduits (Roberts, 2005)
We focus on the collection and interpretation of such a dataset, acquired for the hazardous Lac des Faverges at Glacier de la Plaine Morte (Switzerland)
Two equations are of central importance to characterize the hydraulics and thermodynamics of the lake drainage through a supraglacial channel
Summary
Glacier-dammed lakes are often unstable as ice dams are prone to rapidly fail, which leads to partial or total drainage of the impounded lake through supraglacial, englacial and subglacial conduits (Roberts, 2005). Enlargement of pre-existing veins and conduits (process ii) is possible due to frictional heating (i.e thermal energy dissipation in the water flow due to potential energy release) and/or due to sensible heat fluxes (i.e advection of warm water from the lake). Both processes (ii) and (iii) lead to progressively rising discharge, whereas process (i) often results in a very fast drainage onset and high discharge. These fast lake drainages, so-called glacial lake outburst floods (GLOFs) or “jökulhlaups”, are a serious threat in populated areas and have caused major destruction in the Published by Copernicus Publications on behalf of the European Geosciences Union
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