Today, with few exceptions, streams are adding little material to the beaches; present loss of material from the beaches is essentially a permanent loss. The dominant erosive force is wind-generated wave action; the dominant zone extends from the 50-foot contour to shore. Wave period, length, height, and steepness are important in determining the effect of waves on beaches. Changes in these parameters can be computed for great distances from the fetch area. Short, storm waves drag material from the beach and deposit it in deep water; long swells push offshore material back onto the beach.
Waves breaking on the beach at an angle generate an alongshore current. The velocity of this littoral current increases as the wave period increases, the angle of the wave with short increases, and the slope of the beach flattens. Wave generated by constant trade winds move more than 5 million cubic yards per year along the shore; on most shores the movement is less than 1 million cubic yards per year. Alongshore energy is correlated to sand transport, and from this correlation, it is possible to predict alongshore drift from the incident wave patter. Sand in suspension can be measured in the surf zone, thus aiding the measurement of littoral transport.
The New Jersey shore, 120 miles long and broken by ten inlets, is examined as a field laboratory of shore processes. This shore at the north end is sheltered by Long Island from northeast wave action. Consisting of a nearly continuous series of barrier islands backed by lagoons, the shore has a tide range of about 5 feet, and is subject to attack by northeasters and hurricanes. Wave analyses, based on weather hindcasts for Sandy hook and Cape May, show essentially the same energy pattern at the two points, and that wave energy is greater from the north except in the shadow of Long Island.
Measurements of accretion near Cape May and at Sandy hook indicate long-term rates of drift; successive surveys of eroding shores indicate rates of erosion. Much of the eroded material in the form of silt and clay is lost permanently to deep water; and much of the remaining littoral drift is washed inside the inlets by the flood tides. Understanding the shore processes and their results makes possible the formulation of practical solutions. Temporary solutions involve placing of new sand and the use of groins and seawalls. Long-term solutions will involve control of the inlets with jetties of better design and arrangements for sand bypassing.