Review of a Semi-Empirical Modelling Approach for Cohesive Sediment Transport in River Systems

Bommanna Krishnappan

doi:10.3390/w14020256

Abstract

In this paper, a review of a semi-empirical modelling approach for cohesive sediment transport in river systems is presented. The mathematical modelling of cohesive sediment transport is a challenge because of the number of governing parameters controlling the various transport processes involved in cohesive sediment, and hence a semi-empirical approach is a viable option. A semi-empirical model of cohesive sediment called the RIVFLOC model developed by Krishnappan is reviewed and the model parameters that need to be determined using a rotating circular flume are highlighted. The parameters that were determined using a rotating circular flume during the application of the RIVFLOC model to different river systems include the critical shear stress for erosion of the cohesive sediment, critical shear stress for deposition according to the definition of Partheniades, critical shear stress for deposition according to the definition of Krone, the cohesion parameter governing the flocculation of cohesive sediment and a set of empirical parameters that define the density of the floc in terms of the size of the flocs. An examination of the variability of these parameters shows the need for testing site-specific sediments using a rotating circular flume to achieve a reliable prediction of the RIVFLOC model. Application of the model to various river systems has highlighted the need for including the entrapment process in a cohesive sediment transport model.

Highlights

Cohesive sediments play an important role in the transportation of contaminants and nutrients in a river system
Partheniades, critical shear stress for deposition according to the definition of Krone, the cohesion parameter governing the flocculation of cohesive sediment and a set of empirical parameters that define the density of the floc in terms of the size of the flocs
The objective of this review is to provide guidance for modelling cohesive sediment transport and the associated contaminants in a river system

Summary

Introduction

Cohesive sediments play an important role in the transportation of contaminants and nutrients in a river system. Cohesive sediments are characterized as a mixture of predominantly clay- and silt-sized fractions of clay-type minerals but may contain a range of organic compounds [1]. Contaminants and nutrients interact with these cohesive sediment mixtures and become part of the assemblage of the mineral and organic particles due to physical, chemical and biological controls [2]. The contaminants and nutrients are transported in the river systems predominantly in association with cohesive sediments. A better understanding of the transport processes of cohesive sediment is of paramount importance for understanding the water quality and the quality of the river ecosystem. Transport processes of cohesive sediment were studied extensively in the literature for over sixty years. Partheniades used a rotating circular flume to study the physical behavior of cohesive sediments in the laboratory and concluded that the cohesive sediment behavior is very different from that of the cohesionless coarsegrained sediments, which had been studied extensively in this area of research (see, e.g., [8,9,10])

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