The proglacial control on suspended sediment transfer patterns from a deglacierizing basin, Small River, British Columbia

The extent of the proglacial control on spatial and temporal patterns of suspended sediment transfer was examined at Small River Glacier, British Columbia, a small alpine basin experiencing ice recession from Little Ice Age (LIA) maximum (ca. 1910). An inexpensive, custom-built, datalogger compatible nephelometric turbidimeter (the 'HOBS') was designed to allow a network of instruments to continuously monitor suspended sediment transfer patterns from the entire proglacial area at Small River Glacier. The proglacial channel control on suspended sediment transfer patterns was characterized using a spatially distributed network of 9 gauging stations that provided high frequency (5 min) records of suspended sediment concentration from the entire proglacial area. Multivariate statistics were used to extract and characterize differences in transfer patterns using suspended sediment 'shape' and 'magnitude' classes, without degrading the temporal precision. The statistical analysis showed that transfer patterns differed significantly between gauging stations as determined by the location of the gauging station within the catchment and meteorological conditions. The location of a proglacial gauging station at Small River therefore determined the pattern of sediment transfer observed and confirmed that short-term sediment storage and release of proglacial channel sediment was significantly modifying suspended sediment yield patterns from this basin. Spatially sampled suspended sediment response data from extra-channel surfaces of different maturity during rainfall events was used to infer the timescale of landscape adjustment to LIA deglacierization. Turbidimeters were installed in three ephemeral channels on 'old', 'mature' and 'young' surfaces and their response to rainfall events of different magnitudes recorded. The analysis showed that the intensity and duration of rainfall events had to increase in magnitude to mobilize surfaces of increasing maturity. This rapid temporal decline in surface response indicated that surfaces were stabilizing within decades of exposure from the LIA maximum. However, further perturbation would likely modify this pattern of suspended sediment transfer. Because of this it was suggested that it was difficult to determine when 'paraglacial sedimentation' ceases to influence suspended sediment yields, limiting the utility of the term to describe suspended sediment yield adjustment following deglacierization.