Hindered settling of sand–mud flocs mixtures: From model formulation to numerical validation

Abstract

Mixtures of non-cohesive and cohesive sediment are frequently encountered in natural environments such as estuaries. Depending on the concentration of both species, mixed sediment can record segregation effect or not, behaves like a non-cohesive sediment or like a cohesive sediment. The present study deals with the segregation effect between mud flocs and sand grains during hindered settling. Simulations of this process under various conditions of mixture are proposed by using two coupled mass conservation equations which are solved by a high order numerical model. Specific closure equations are proposed herein for the hindered settling of sand–mud mixed sediment. Comparisons between simulations and experiments are presented on vertical concentration profiles during the segregation process. Obviously, the model enables the description of hindered settling for pure non-cohesive (or pure cohesive) case and the segregation for bi-disperse suspensions.