CGRG Bibliography of Canadian Geomorphology
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Author : Church, M.A.; and Tunnicliffe, J.
Date : 2009.
Title : Patterns of post glacial sediment yield in Chilliwack Valley, British Columbia.
Publication : 2009 American Geophysical Union Fall Meeting. December 14-18, 2009. San Francisco, California, USA.
Issue :
Page(s) :
Abstract
The connectivity between the hillslope system and the fluvial network over post-glacial time (13.5k cal. years) is examined in a large (1 230 km^2), formerly glaciated catchment in southwest British Columbia. Volumetric erosion estimates for sand and gravel were generated for open slopes using a non-linear diffusion equation. Eroded volumes from major gullies and valley fills were estimated by extrapolating across formerly continuous surfaces such as till blankets and terraced remnants of glaciofluvial valley fills. Deposition volumes at the outlet of catchments were estimated at successive scale orders by approximating the geometry of detrital accumulations such as fans and cones using geometric CAD representations. The mean deposition ratio (Deposition / Erosion) declines with increasing scale order due to sorting and onward remobilization of the coarse sediment mass. A simple mass balance model shows much higher rates of trapping (up to 60% of the coarse sediment load) within catchments that are less than 10 km^2 in size. Trapping tends to occur where relatively low-order (1-4th order) hillslope and tributary catchments join larger (5-8th order) valley streams, depositing their coarse textured load due to the pronounced change in channel gradient. Connectivity within the fluvial system is controlled by floodplain storage in the broad, glacially carved valleys. Fall in valley base-level over post-glacial time acts to further moderate hillslope storage and the supply of sediment to the fluvial system by reactivating remnant fills and the fans that line the margins of the major valleys. The periodic remobilization of these relict sediment stores leads to a pattern of increasing specific sediment yield downstream for larger tributaries and the valley mainstem. These observations have important implications for the sediment balance amongst catchments of varying size within the drainage network. After 10^4 years, the system remains in disequilibrium.
Bibliography of Canadian Geomorphology