UBC Theses and Dissertations
Alpine proglacial stream temperature dynamics Richards, John
This study was motivated by an interest in understanding the effects of glacier retreat on late summer stream temperatures in an above-treeline proglacial stream and lake system in the southern Coast Mountains of British Columbia, Canada. Fieldwork was carried out during August and September of 2007 and focused on thermal processes controlling water temperature in the proglacial lake and a 1 km alpine reach directly downstream of the lake outlet. The proglacial lake was small (0.07 km²), featured a single inflow and outflow channel and had a residence time of approximately 4 days. The alpine reach featured continual cascading flow (25% channel gradient), marked diurnal fluctuations in discharge and variable terrain shading. It was found that warming between the inflow and outflow of the lake (1.8°C, on average) was controlled by the total heat content of the lake and cycles of mixing and stratification. A heat budget analysis indicated that the heat content of the lake was dominantly controlled by absorbed shortwave radiation and the advective effect of the inflow and outflow streams. Application of a dynamic reservoir model (DYRESM) to model observed lake temperatures (inflow, outflow and a temperature-depth profile), and comparison to other studies, suggested that suspended sediment concentration in the inflow had a dominant control on lake mixing and stratification. Based on equations developed from low-gradient channels, a stream energy budget model failed to replicate observed downstream warming rates. A spatially distributed net radiation model, along with statistical modification of the energy budget, provided insight into the processes that control stream temperatures in alpine areas. The final hybrid model showed a good match with observed downstream warming. This model accounted for the variation of width and albedo with discharge, and the spatial variability in net radiation due to topographic shading and the slope and aspect of the channel. The model also included parameters that increased the sensible and latent heat fluxes relative to values calculated from standard equations, which is consistent with the hypothesis that these fluxes are enhanced by cascading flow.
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