Morphodynamic Modeling of Sediment Pulse Dynamics

Abstract

Sediment pulses, defined as discrete, temporary increases in sediment supply, enter channels through both natural and anthropogenic means. The movement of the resultant deposit (sediment wave) in coarse-bedded channels is generally characterized by some combination of translation and dispersion; however, how sediment waves evolve over time is still poorly understood, potentially hampering restoration efforts that involve the introduction of sediment to channels. Here we use a one-dimensional morphodynamic model to explore how different pulse characteristics affect sediment wave movement. Our one-dimensional model uses the standard step backwater method to compute hydrodynamics and determines morphodynamics by computing bedload transport and retaining vertical grain size stratigraphy. We explore the effect of pulse mass, initial wave spread, and composition (grain size) on subsequent sediment wave dynamics. Our results suggest higher relative rates of sediment wave dispersion to advection for larger pulses, waves with a smaller initial spread, and pulses composed of coarser material. In all simulations sediment wave celerity and spreading rates decayed through time as a power function. Waves of smaller total mass decayed at faster rates than those of larger mass. Simulations also show that sediment pulses attain a terminal amplitude, suggesting that some sediment waves may not completely disperse. Larger terminal amplitudes were associated with larger pulses and pulses composed of coarser grains.