Noncohesive Sediment Transport Modeling with Multiple Size Classes

Abstract

Contemporary three-dimensional sediment transport models are computationally expensive and thus a compromise must be struck between accurately modeling sediment transport and the number of effective size classes to represent in such a model. The Environmental Fluid Dynamics Code (EFDC) was used to model the experimental results of Yen and Lee who investigated sediment erosion and gradation around a 180-degree bend subject to transient flow. The EFDC model was first calibrated using the eight distinct size classes reported in the physical experiment to find the best erosion formulations to use. Once the best erosion formulations were ascertained, numerical simulations were carried out for each experimental run using a single effective particle size. Four techniques for evaluating the effective particle size were investigated. Each procedure yields comparable effective sizes, each within a factor of 1.5 of the others. Model results indicate that particle size as determined by the weighted critical shear velocity most faithfully reproduced the experimental results for erosion and deposition depths. Subsequently, model runs were conducted with different numbers of size classes to determine the optimal number that yields an accurate estimate for noncohesive sediment transport. Results from this study indicate that using three effective size classes to estimate the distribution of sediment sizes is optimum. In addition, when modeling only one non-cohesive size class, the best technique for calculating effective particle size is to use a weighted critical shear velocity.