Geomorphic and Fluvial Response to Recent Permafrost Disturbances in a High Arctic River, Cape Bounty, Nunavut

Abstract

Using a sediment budget approach, suspended sediment transport dynamics were studied over the 2010 summer runoff season in the 8 km2 West River catchment at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut. Research was carried out in an effort to determine the longer term impacts and response of recent (2007-8) active layer detachments (ALD) on the river system. In 2010, measured ALD inflows contributed 4.7% of the measured sediment yield, a decrease of 13.3% from 2007 when they initially formed. This indicates that while they continue to supply sediment to the main river, the impact they have on sediment fluxes, and hence the sediment budget has diminished, with time. Results from the sediment budget indicate that connectivity and the sediment delivery ratio within the system have also decreased with time. Sediment budget analysis shows that in response to this additional sediment, the West River progressively stores more sediment throughout the season, storing as much as 85% of sediment inflows during baseflow. Sediment was preferentially deposited within the channel, with coarser material deposited in the upper reaches, and finer material deposited in the lower reaches. Similarly, the transported and stored sediment became progressively finer with time, indicating the importance that river competence and wetted perimeter have on sediment transport as the larger sediment was entrained earlier in the season under higher flow conditions when the sediment was accessible, and finer sediment transported later in the season due to decreased competence and reduced accessibility of sediment. This sediment storage is expected to replenish sediment in the channel that is eroded during peak discharge in spring, and also dampens the effects that disturbances have on the sediment budget through storage. Sediment stored in the channel towards the end of the season does not contribute to sediment yield and may prove to be an important source of sediment in future years under late summer rainfall events.