CHAPTER 4 

 LITTORAL PROCESSES 



I. INTRODUCTION 



Littoral processes result from the interaction of winds, waves, currents, 

 tides, sediments, and other phenomena in the littoral zone. This chapter 

 discusses 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 of 

 other coastal structures. Therefore, an understanding of littoral processes 

 is needed to predict erosion or accretion effects and rates. A common aim of 

 coastal engineering design is to maintain a stable shoreline where the volume 

 of 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. 



1, 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 

 App. A). 



a. Bgach Profile . Profiles perpendicular to the shoreline have char- 

 acteristic features that reflect the action of littoral processes (see Fig. 1- 



1, Ch. 1, and Figs. A-1 and A-2 of the Glossary for specific examples). At 

 any given time, a profile may exhibit only a few specific features; however, a 

 dune, berm, and beach face can usually be identified. 



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

 Figure 4-1 by a series of profiles taken between February 1963 and November 

 1964 at Westhampton Beach, New York. The figure shows how the berm built up 

 gradually from February through August 1963, cut back in November through 

 January, and then rebuilt in March through September 1964. This process is 

 typical of a cyclical process of storm-caused erosion in winter, followed by 

 progradation owing to the lower, and often longer, waves in summer. 



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

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

 indented, where sand is restricted to local pocket beaches; 4- 2b a long 

 straight coast with an uninterrupted sand beach; and 4-2c short barrier 

 islands interrupted by inlets. These are some of the different coastal 

 configurations which reflect differences in littoral processes and the local 

 geology. 



2. Environmental Factors . 



a. Waves. The action of waves is the principal cause of most shoreline 

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



4-1 



