Hydroclimatic influences on suspended sediment delivery in a small, High Arctic catchment

Abstract

A study of suspended sediment transport dynamics was undertaken in the West River at Cape Bounty, Melville Island, Nunavut. Hydrometerological conditions and sediment transport were measured over three seasons in order to characterize suspended sediment transport and grain size characteristics in relation to catchment and channel snowpack. Catchment snow water equivalence was measured at the beginning of the season, and discharge, suspended sediment concentration (SSC) and grain size were measured at high temporal resolution through the runoff period to evaluate diurnal-, event- and seasonal-scale discharge-suspended sediment and grain size hysteresis. In addition, two models of a time-integrated suspended sediment trap, modified from Philips et al. (2000), were deployed in both streams to assess the representativeness of the captured sediment. The West stream discharge was dominated by the snowmelt peak in all three seasons. From 54-96% of suspended sediment was transported during this short period, although hysteresis relationships indicate that delivery of sediment and water were not synchronous and interannual relationships suggest disproportionate increases in sediment discharge with increased catchment snowpack. Clockwise and counter-clockwise suspended sediment hysteresis relationships were apparent and associated with lesser and greater snowpack, respectively. Additionally, grain size hysteresis suggested variable sediment sources during the season. Assessment of the time-integrated suspended sediment trap in the East and West streams illustrated that the captured material was not representative of the ambient stream conditions. Captured mass was typically two orders of magnitude less than expected iii capture rates (<1%) and that the captured sediment was significantly coarser than the ambient stream suspended sediment load. Investigations of suspended sediment transfer in this small, High Arctic catchment reveal that sediment transport increased with increased catchment snowpack, but delivery of water and sediment were not synchronous during the nival discharge event suggesting changing sediment accessibility during the season. An attempt to collect a time-integrated suspended sediment sample that would incorporate variability in the character and magnitude of sediment delivery provided an unrepresentative sample, but results indicate that a detailed examination of hydraulic relationships between the trap and ambient conditions could ultimately lead to the development of a more representative trap.