1. INTRODUCTION 



1.1 Coastal Currents and Sediment Transport 



The Corps of Engineers are responsible for a variety of coastal projects 

 such as the deepening of navigation channels, the disposal of dredged 

 materials, and the construction of shore protection structures. These coastal 

 projects are influenced by, and in return can influence, the existing 

 hydrodynamic and sedimentary regimes of the coastal environment. Before a 

 coastal project can be carried out, impact analyses should be performed to 

 ensure that both economic efficiency and environmental quality will be 

 optimally maintained. As a first step, existing hydrodynamic and sedimentary 

 regimes in the coastal environment should be quantitatively studied. Next, 

 impact due to a number of alternative plans for the coastal project should be 

 quantitatively assessed. To meet both these requirements, an accurate 

 predictive tool for coastal currents and sediment transport is urgently 

 needed. Physical models and field and laboratory studies may be used to aid 

 the ultimate construction of a comprehensive mathematical model. 



In a broad sense, coastal water starts from the shoreline and extends 

 seaward much farther beyond the wave breaking zone to the continental shelf 

 where water depth may be several hundred meters. As such, coastal currents 

 are influenced by fresh water river inflow, wind, tide, and large-scale ocean 

 circulation. At the ocean surface, short-period wind waves are generally 

 present whose effects can reach the bottom of shallow coastal waters. In the 

 water column, the water is generally turbulent with strong mixing. Relatively 

 slow internal waves may also be present. With the additional influences of 

 earth rotation and complex coastal geometry and topography, the hydrodynamic 

 regime within a coastal environment is extremely complicated. 



Sediment transport in a coastal environment is strongly influenced by the 

 hydrodynamic regime. Sediments enter into the coastal environment via fresh 

 water inflow during high runoff periods, erosion of the shoreline, and 

 disposal of dredged materials. Generally, relatively fine clay and silt 

 particles comprise a major portion of these sediments. These sediments can be 

 transported by the coastal currents over some distance before depositing on 

 the ocean bottom. Strong coastal currents and/or high waves can cause 



