Analysis and Comparisons of Degradation Models

Abstract

Construction of a dam is one of the most common causes of channel degradation. The major differences among several well‐known mathematical degradation models are classified. The analytical degradation model is based on the solution of a diffusion equation, which is converted from the governing equations using kinematic wave assumption. Most of the explicit models are similar, but differ in terms of the calculation of longitudinal sediment distribution to update the channel bed profiles at each time step. The explicit model proposed by Gessler is simpler than other explicit models. Laboratory data previously collected at Colorado State Univ. for degradation study in a prismatic channel with nearly uniform sediment sizes are used to compare the results predicted by different explicit and implicit models. Gessler's model produces rather accurate results for flow conditions with high Froude number (but still subcritical flow) in a prismatic channel. Results from the central difference scheme as used in HEC‐6 for the longitudinal sediment distribution appears to agree well with the collected flume data. The difference between the actual sediment load and the sediment transport capacity within the “distance of concentration recovery” has to be considered for modeling the degradation process. Comments are made about the applicability and limitations of different models. The variation of roughness during degradation is also analyzed.