ERDC/CHL CHETN-II-44
September 2001
Figure 2. Monmouth Beach, NJ, September 1996
Residual Fill Bathymetry: If material is placed irregularly alongshore and seaward of the
depth of closure, then the nearshore contours will be altered by the presence of the fill. Wave
refraction over irregular contours will tend to cause a systematic pattern of convergence and
divergence of breaking waves (see type 11). Different wave heights and directions along the
beach will produce areas of varying erosion and accretion until the residual material disperses.
Permanent Offshore Loss: Losses of littoral material to submarine canyons has been long
documented on the coast of CA (e.g., Everts et al. 1987), and material can be lost as well to deep
navigation channels, such as to the channel system located offshore of Sandy Hook, NJ. On a
local scale, this process was identified by Raichle, Elsworth, and Bodge (1998) for a nourished
beach in Broward County, FL. Sediment appeared to be transported offshore and over or
through a reef. The reef acted as a rectifier, allowing sediment to move offshore but not over it
and onshore.
Wave Transformation by Offshore Translation of Beach Fill: Dean, Liotta, and Simn
(1999) postulate that a beach fill with irregular translation offshore will create a nonuniform
distribution in wave energy alongshore because the offshore bathymetric contours will not be
uniform. EHSs are expected to occur leeward of concentrations of wave energy and ECSs to
occur at locations of reduced wave energy.
Wave Transformation by Offshore Bathymetry: Wave refraction diagrams developed
even prior to the modern computer age showed that irregular bottom contours produce wave
convergence and divergence along the coast. Here, offshore refers to the area from deep water
for the characteristic wave period of the coast to the outer edge of the typical surf zone or the
average-annual depth of closure. EHS type 3, borrow pit within active zone, is an example.
Examination of long-term shoreline change data for many locations reveals highly variable rates
of change and locations of significantly elevated rates of erosion. Along coastal Delaware,
several EHSs correspond to irregular shoreface bathymetry in the form of linear sand shoals or
ridges. McBride and Moslow (1991) postulated that the sand ridges are remnants of ebb shoals.
The sand ridges focus wave energy on segments of the shoreline by wave refraction. Galgano
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