CHAPTER 4 



LITTORAL PROCESSES 



4.1 INTRODUCTION 



Littoral processes result from the interactions among winds, waves, 

 currents, tides, sediments, and other phenomena in the littoral zone. The 

 purpose of this chapter is to discuss those littoral processes which involve 

 sediment motion. Shores erode, accrete, or remain stable, depending on the 

 rates at which sediment is supplied to and removed from the shore. Excessive 

 erosion or accretion may endanger the structural integrity or functional 

 usefulness of a beach, or other coastal structures. Therefore an under- 

 standing of littoral processes is needed to predict erosion or accretion 

 rates. An aim of coastal engineering design is to maintain a stable shore- 

 line where sediment supplied to the shore balances that which is removed. 

 This chapter presents information needed for understanding the effects of 

 littoral processes on coastal engineering design. 



4.11 DEFINITIONS 



In describing littoral processes, it is necessary to use clearly 

 defined terms. Commonly used terms, such as "beach" and "shore," have 

 specific meanings in the study of littoral processes, as shown in the 

 Glossary. (See Appendix A.) 



4.111 Beach Profile . Profiles perpendicular to the shoreline have char- 

 acteristic features that reflect the action of littoral processes. (See 

 Figure 1-1, Chapter 1, and Figures A-1 and A-2 of the Glossary for spe- 

 cific examples.) At any given time, a profile may exhibit only a few 

 specific features, but usually a dune, berm and beach face can be identi- 

 fied. 



Profiles across a beach adapt to imposed wave conditions in ways as 

 illustrated in Figure 4-1 by a series of profiles taken between February 

 1963 and November 1964 at Westhampton Beach, N.Y. The figure shows how 

 the berm built up gradually from February through August 1963, then was 

 cut back in November through January, and was rebuilt in March through 

 September 1964. This process is typical of a cyclical process of storm 

 erosion in winter and progradation with the lower, and often longer, 

 waves in summer. 



4.112 Areal View . Figure 4-2 shows three generalized charts of different 

 U.S. coastal areas, all to the same scale. Figure 4-2a shows a rocky coast, 

 well-indented, where sand is restricted to local pocket beaches. Figure 

 4-2b shows a long straight coast with an uninterrupted sand beach. Figure 

 4-2c shows short barrier islands interrupted by inlets. These are some of 

 the different coastal configurations which reflect differences in littoral 

 processes and the local geology. 



4.12 ENVIRONMENTAL FACTORS 



4.121 Waves . Water waves are the principal cause of most shoreline 

 changes. Without wave action on a coast, most of the coastal engineering 



4-1 



