THE INTERNAL VELOCITY FIELD IN BREAKING WAVES

Abstract

As far as is known, the results presented here are the first detailed measurements of the horizontal velocity component inside breaking waves. The field study was originally undertaken in 1960 to determine the presence and strength of mid-depth return flow under shoaling waves (Miller and Zeigler, 1961, 1964). In the course of the experiment, a series of measurements was made very close to the shore. During one tidal cycle, the instruments became exposed to breakers, and continued to operate. A study of the resulting data convinced us that detailed velocity measurements could be made within the natural breaker m the field. Accordingly, a series of runs was made and velocity data collected on breakers ranging from very small to storm size. This data will be presented and discussed in detail in a later portion of this paper. A number of laboratory studies have been made on breakers. These may be placed in three categories for our purposes. The first group includes detailed discussion of observations and sequential figures illustrating the development of breakers. An example is Mason (1951). The second group of papers gives some detail on the structure of breakers and presents, either by direct photograph or sketch of, the trajectory inside the breakers. Examples are Hamada (1951) and Morison and Crooke (1953). The third group of papers presents, in addition to most of the material referred to above, a series of vector maps of the internal velocity under various types of breakers, including both sinusoidal and solitary wave generated breakers. Papers in the third category include Iversen (1951), Larras (1952), and Ippen and Kulin (1955). The latter were of most direct interest to us within the context of the present study.