A critical perspective on 1-D modeling of river processes : gravel load and aggradation in lower Fraser River.

Abstract

We investigate how well a width-averaged morphodynamic model can simulate gravel transport and aggradation along a highly irregular 38-km reach of lower Fraser River and discuss critical issues in this type of modeling. Bed load equations with plausible parameter values predict a gravel input consistent with direct measurements and a sediment budget. Simulations using spatially varying channel width, and forced by dominant discharge or a 20-year hydrograph, match the observed downstream fining well. They reproduce major qualitative features of a 47 year sediment budget and match maximum local rates of aggradation and degradation to well within a factor of 2. Locations and rates of aggradation and degradation are influenced by channel constrictions. Runs for single years of unusually high or low peak discharge suggest that the main transfers of gravel occur in different parts of the reach in different years. One-dimensional morphodynamic modeling of highly nonuniform rivers has serious conceptual limitations but may be a valuable complement to empirical approaches.