Regional clastic sediment yield in British Columbia

Abstract

The data archive of the Water Survey of Canada, supplemented by data of the British Columbia Hydro and Power Authority, is used to investigate the areal pattern of fluvial sediment yield in British Columbia. The data represent suspended-sediment loads at 63 stations derived from observations within the period 1966–1985. In most of the province there is a single annual peak in sediment transport in spring, corresponding to the dominant snowmelt freshet. However, on the coast winter rainfall induces the sediment peak, and in the Coast and Cascade mountains there is a transitional regime with two peaks. From 65 to 90% of annual sediment yield occurs in the spring three months. Sediment yield per unit area (specific sediment yield) increases with drainage area at all scales from 10 up to 30 000 km2. The pattern persists seasonally throughout the year. This contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from erosion of the land surface. In British Columbia much of the sediment derives from erosion of Quaternary materials along stream banks and valley sides. Rivers draining glaciers and lakes behave distinctively. The observed pattern of sediment yield complicates prediction of drainage-basin sediment yield.