A computational distributed gravel budget for the lower Fraser River, British Columbia

摘要

A depth-averaged 2D model is used to compute a distributed sediment budget for a gravel-bed reach of lower Fraser River. The model couples the hydrodynamics and bedload transport of multiple size fractions, and computes bed level changes on a curvilinear grid. Bedload transport, surface coarsening, spatial variation in the size distribution, and morphologic change are calculated, for five steady discharges. For each discharge, longitudinal variation in bedload transporting capacity is determined by integrating transporting capacity across the channel at each 50 m section, defining zones of aggradation and degradation. A bedload transport rating curve is developed at the boundary of each zone, and the mean annual bedload transport across each boundary is obtained. The distributed sediment budget is determined. This yields average annual rates of gravel aggradation and degradation volumes for each zone. The computed sediment budget agrees well with results based on high quality field measurements of gravel transport.