NUMERICAL INVESTIGATION OF BEACH PROFILE EVOLUTION USING A NEW SEDIMENT CONCENTRATION MODEL

Abstract

Beach profile change largely depends on sediment transport and its settlement. Sediment transport in coastal waters occurs primarily due to the suspension mechanism. Sediment suspension frequently takes place in and outside the surf zone due to (1) vortices generated by sand ripples, (2) the movement of the bottom layer with high bed shear stresses, and (3) the turbulence generated by wave breaking (Jayaratne and Shibayama, 2007). There is a significant knowledge gap in the complete understanding of ripple and sheet-flow dynamics due to its complexity. A number of sediment transport and beach profile evolution models have been developed over the recent decades. However their applicability to the coastal environment changes from one environment to another due to the presence of many governing parameters in these models. This paper discusses two different types of sediment concentration models and their performance for beach profile modelling. The focus is on the models of Jayaratne and Shibayama (2007) and Jayaratne et al. (2011), both highlighting a methodology to calculate sediment concentration with improved accuracy and governing physics. Introduction In recent years, the utilization of coastal areas has increased for human activities such as recreation, leisure, tourism and transportation. Protection of the coastal areas from wind-induced waves and catastrophic events like storms and hurricanes has become a crucial and challenging task. Coastal zone management requires an accurate predictive capability that represents beach deformation from closure depth up to the swash zone. To develop an accurate beach profile model is a challenging task due to the complexity of the sediment transport in the surf zone and swash zone and also its hydrodynamics. A large number of beach profile models have been developed mostly using empirical hydrodynamic equations [Baldock et al. (2011), Roelvink et al. (2010), Sasaoka et al. (2009), Suzuki and Kuriyama (2008), Ruessink et al. (2007) etc.]. Often wave, current, sediment and beach-profile change data both from field and 026 18/3/2015