Downstream Patterns and Catchment Controls on Suspended Sediment Transport in a High Arctic River

Abstract

A study of downstream suspended sediment transport dynamics in the West River at Cape Bounty, Melville Island, Nunavut, was undertaken in 2012. The first component of the research quantified the sediment mobilized in the West River during the 2012 season. A nival bed-contact survey was undertaken to identify areas of the river in which stream flow was isolated from the bed, and was combined with a reach-based sediment budget approach to assess sediment entrainment and downstream movement. This analysis revealed the propensity of the West River to store suspended sediment through much of the season. Permafrost disturbances in 2007 inundated the West River with fine sediments, the majority of which are progressing from the headwaters as a sediment slug that is subject to substantial downstream storage. Diurnal and event hysteresis analysis from 2004-2012 demonstrate the change in sediment delivery inter-annually, transitioning from a system characterized by clockwise hysteresis prior to the 2007 disturbances, to counter-clockwise hysteresis post 2007. The latter is reflective of the important contribution of the headwater sediment slug from disturbance to downstream sediment transport and common net sediment storage in the lower reaches of the river. The second project studied the delivery of suspended sediment following late season major rainfall events (MRE) and the control antecedent catchment conditions prior to rainfall exert on the magnitude of stream runoff and suspended sediment transport. Two MREs on July 9 and July 23, totalling 35.4 and 10.6 mm, respectively, resulted in exceptionally low discharge response and sediment mobilization. Analysis of synoptic level pressure patterns and catchment soil moisture revealed low volumetric water content preceding both MREs, a result of sustained exceptional early summer warmth under stable regional high pressure. Compared to similar MREs in 2007-2009, the soil in 2012 did not become saturated, and substantial runoff did not occur. These studies contribute to an understanding of the processes of sediment transport in response to disturbances, rainfall, and antecedent catchment conditions, all of which are becoming important components of the Arctic fluvial systems but have had limited study due to the emphasis on snow melt processes and hydrological fluxes.