in which all terms are expressed as a volume or as a volumetric change rate, Qsource and Qsink
are the sources and sinks to the control volume, respectively, DV is the net volume change
within the cell, P and R are the amounts of material placed in and removed from the cell,
respectively, and residual represents the degree to which the cell is balanced. For a balanced
cell, the residual is zero. Fig. 2 shows the parameters in Eq. (1) for a typical sediment budget
cell in this study, in which x1 and x2 represent alongshore coordinates of the cell according to
the established baseline which roughly parallels the shoreline.
∆V, P, R
Qsink (sea level)
Fig. 2. Typical sources, sinks, and engineering activities
formulated for each sediment budget cell.
Shoreline Position Data
Ten historical shoreline position data sets were available to formulate the sediment
budget: 1830, 1870, 1887, Feb-May 1933, Oct 1938, Mar 1962, and Dec 1979 (Leatherman
and Allen 1985), Apr 1983, Mar 1988, and Mar/Apr 1995. The first four data sets were
derived by Leatherman and Allen (1985) from the U.S. Coast and Geodetic Survey maps, in
which the shoreline position is believed to represent the high water or berm crest line
(Shalowitz 1962). The 1938, 1962, and 1979 shoreline position data sets were digitized from
aerial photography by Leatherman and Allen and according to their description represent
"mean high tide shorelines." The latter three data sets were digitized from the interpreted
high water line (HWL) shoreline position on digitally rectified scanned aerial photography as
a part of this study. All shoreline position data were described at 25-m intervals with respect
to an established baseline for each barrier island. Each baseline has its origin in the center of
the inlet and is oriented with the general trend of the shoreline. With exceptions for the 1938
and 1962 (post-storm) data, it is believed that this suite of data provides a fair representation
of the same discernable feature, i.e., the seaward-most berm crest or high water line.
Volumetric change rates were calculated from the shoreline change rates by assuming that
the shoreline is translated over an active depth DA(x), where the active depth is given as the
sum of B(x), the elevation of the seaward-most active berm relative to a datum, and DC (x),
the depth of closure measured from the same datum, and x is the distance alongshore.
Rosati et al.