11.1 Introduction

One of the most important reasons for studying nearshore currents is to help understand the interaction between the shoreline and the fluid motion in the sea. In the past, geographers and geomorphologists accumulated a good deal of descriptive knowledge on the formation and evolution of coastlines (Johnson, 1919; King, 1959; Zenkovich, 1967; Shepard and Wanless, 1973). Since the loss of sand and the recession of beaches can be undesirable to parks, residential areas, and coastal highways, and the accumulation of silt near a harbor entrance or a river inlet can be hazardous to navigation or flood control, it is the task of engineers to grapple with the mysteries of beach processes in order to plan proper defenses.

Most of the guidelines for coastal protection practices have been based on observational studies both in the field and in the laboratory (see, for example, Shore Protection Manual, U.S. Army Coastal Engineering Research Center, 1977, Vols. I-III). These studies have been and will undoubtedly remain indispensible in increasing our knowledge of shore processes. In recent years, much progress has also been made in the development of semiempirical theories on both the causative currents and the resultant sediment motion. The whole problem of shoreline dynamics is extremely complex, due in part to the turbulent interaction between sediments and fluid flow and in part to the large variety of currents that can be present (wind waves, tides, storm surges, river currents, and large-scale ocean circulation caused by wind, thermal or salinity gradients,...