Three- Dimensional Numerical Simulation of Cohesive Sediment Transport in Natural Lakes

Abstract

Sediment has been identified as one of the leading nonpoint-source pollutants. Most sediments are transported into surface water bodies from agricultural lands and watersheds through runoff, and greatly affect the surface water quality. Sediment particles will change channel topography and play an important role in affecting water quality physically or chemically by the pollutants, nutrients and pesticides they carried. Shallow lakes in the Southern U.S. are often surrounded by agriculture lands. The suspended sediments in these shallow lakes are normally very fine, and they can be classified as cohesive sediments. The basic processes involved in cohesive sediment transport, such as flocculation, deposition, erosion, consolidation, etc., have been studied by many scientists. Burban et al. (1990) presented a formula to calculate the settling velocity of flocs in fresh water based on laboratory experiments. Thorn (1981), Ziegler and Nisbet (1995), Li and Mehta (1998) established several empirical formulas for settling velocity of flocs by considering the effects of sediment size, sediment concentration, salinity, turbulence intensity, and bed shear stress. Krone (1962) and Mehta and Partheniades (1975) investigated deposition of cohesive sediment and proposed formulas to estimate deposition rates. Partheniades (1965) proposed a formula to calculate the erosion rate of cohesive sediment. Hamm and Migniot (1994) studied the consolidation of cohesive bed material using an approach of three stage process. In recent decades, some researchers have studied the cohesive sediment transport in rivers, lakes, and coastal waters using numerical models. Willis and Krishnappan (2004) reviewed a number of numerical models and gave an overview of the knowledge base required for modeling cohesive sediment transport in river flow. Nicholson and O’Connor (1986) developed a 3D cohesive sediment transport model using a splitting method in conjunction with a characteristics technique and a mixed explicit-implicit finite difference approach. Ziegler and Nisbet (1995), Bailey and Hamilton (1997), and Wu and Wang (2004) developed several two-dimensional (2D) depth-averaged models to simulate cohesive sediment transport. Liu (2007) developed a vertical (laterally integrated) two-dimensional model to simulate the cohesive sediment transport in Danshuei River estuary by considering the effects of reservoir construction upstream of the river. Normant (2000), Jin and Ji (2004) proposed 3D layer models to simulate the cohesive sediment transport in estuaries and lakes, respectively. Sediment erosion, transport and suspension often result from turbulent flows. In inland lakes, however, the water flow is often dominated by wind, and the wave induced by wind