Numerical Simulations of Coastal-Tract Morphodynamics

A finitv difference nttrnedcal model has been developed to represent the large-scale morphodynamics of complex coastal systems. The model is based on the Coastal System Tract (CST) concept. This model contains representations of coastal features such as tidal inlets, bays and rivers, beach systems (including littoral drift and profile migration), as well as the offshore zone comprised of the shoreface, shelf and upper continental slope. The purpose of the model is to diagnose the large-scale morphodynamical interactions between the components of the CST that have previously only been represented as separate or incompletely link dements. The results show that there are important forcing factors that result from different characteristic response times of the independent system components. This means that the system components are never properly tuned to respond in unison to perturbations in the large-scale forcing parameters. INTRODUCTION The need to plan and engineer coastal facilities, such as ports or offshore artificial islands that do not upset area-wide coastal processes, has focused attention on a need for long-term and large-scale quantitative representations of large coastal systems morphodynsmics, Over the past decade it has become increasingly apparent that representing the complex processes that shape open-ocean coastline with mathematical models provides for quantitative diagnosis of the relationship between environmental forcing and morphological response. Because coastal systems are complex assemblages of subeomponents and because many available models operate with time steps that resolve wave motions (i.e. seconds), it has been common practice to consider relatively short-term processes (less than a decade) and to isolate portions of overall coastal systems for study (e.g. the surf zone, inlets or the shoreface). More recently, models have been developed to represent large-scale and long-term processes and to link some of the components of overall open-ocean coastal systems. The time-, and length-scales of interest are decades to centuries and tens to hundreds of kilometers. This paper reports on the development and application of a large-scale numerical model representing an entire coastal system tract. It allows exploration of interactions between the shoreline sediment sources and sinks (e.g. river mouth, tidal inlet), the surf zone littoral sediment Vice-President, URS, 3676 Hartsfield Road, Tatlahassee. FL 32303 USA. Alan niedoroda@urscorp.com z Sefflor Project Scientist, URS, 3676 Hartsfield Road, Tallahassee, FL 32303 USA. Chris reed@urscorp.com Pro~ssor, Delf University of Technology, Faculty of Civil Engineering and Geosciences, Delf Hydraulics, (P.O. Box 177, 2600 MH) Delft, The Netherlands. Marcel.stive@wdelft.nl 4 Professor, Institute of Marine and Ocean Sciences, University of Sydney, NSW 2006, Australia. P.cowell@csu.usyd.edu.au