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Hydrology and thermal regime of a proglacial lake fed by a calving glacier

University of British Columbia

This study was motivated by an interest in understanding the physical processes driving the thermal regime of an ice-contact proglacial lake, in the context of its influence on downstream water temperatures in the southern Coast Mountains of British Columbia, Canada. Field work was carried out at Bridge Glacier during the 2013 summer melt period, from June - September, focusing on quantifying the heat and water budgets and the thermal structure of the lake. The proglacial lake extending from the terminus of Bridge Glacier, informally referred to as `Bridge Lake', was approximately 5.9 km² and discharged via a single outlet. A barrier of icebergs caused the ice-proximal and distal portions of Bridge Lake to behave as individual basins, although not separated by a sill. The mean net warming in summer 2013 between the glacier terminus and lake outlet was 2.7 °C. Net radiation provided the dominant energy input and net lateral advection was the dominant energy sink. The presence of icebergs provided a significant energy sink and source of 0 °C melt water. Iceberg melt was equivalent to 6 - 7% of the mean discharge measured at the lake outlet. As icebergs are lost from Bridge Lake with continued glacier retreat, lake discharge is expected to decrease, having detrimental impacts on downstream water supplies for use in hydropower. The vertical thermal structure of the water column was monitored at 8 locations within the distal basin, with varying degrees of stratification observed with increasing distance from icebergs. Suspended sediment concentrations were inferred to dominate density variations, inhibiting vertical mixing of the water column induced by temperature differences. A modelling exercise provided predictions of changes to the thermal behaviour of Bridge Lake with the removal of icebergs once Bridge Glacier becomes land-terminating and ceases to calve icebergs. With the loss of icebergs, Bridge Lake is predicted to exhibit higher water temperatures and elevated advective energy transfer associated with outflow. Drawing upon previous studies and findings from the current study, a conceptual model for the effect of valley glacier retreat on downstream water temperatures is proposed.

Text

2014-08-19

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50031

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/