Tidal Cycle of Changes in an Equilibrium Beach, Sandy Hook, New Jersey

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Abstract
Repeated transverse profile surveys were made in the summers of 1959, 1960, and 1961 on the Atlantic beach of Sandy Hook, New Jersey. The beach experienced accretion (progradation) throughout early and middle summer at the same time that a summer berm was built. By late July progradation largely ceased, yielding an equilibrium profile closely fixed in position and slope. Superimposed upon the late-summer steady state are rhythmic minor changes in beach profile attending the semidaily tidal cycle in which the swash-backwash zone and breaker zone shift up and down the foreshore. Elevation changes at selected points on the foreshore transverse profile were measured at half-hour intervals using engineer's level, level rod, and steel tape. From accumulated level data, a model cycle was synthesized to represent elevation and form changes at various levels on the beach. As tide rises, a short phase of initial deposition of about 0.02 foot of medium sand takes place near the inner limit of swash. There follows a scour phase in which about 0.2 foot of sand is removed in a period of 1 1/2-2 hours. Scour is followed by deposition, representing advance of a wedge of mixed sand and pebbles, terminating in the well-sorted pebble and gravel step formed under the breaker point. As step-phase deposition continues, median diameter increases, and sorting becomes poorer. Total step deposition ranges from 0.5 to 0.7 foot. During falling tide, changes at a given survey point are repeated but in reverse order. Thus, under equilibrium conditions, the beach is restored to its original elevation, slope, and composition. About 0.2 foot of sand is completely removed and redeposited during each cycle at points in the mid-tide region of the zone of swash and backwash under characteristic summer wave conditions.

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