South Spit/South Beach
Figure 32 illustrates the complex changes to the south spit as it first migrated
south and west into south Chatham Harbor and then overtook the south flood
shoal and south remnant sand flat to form the land bridge between the mainland
and South Beach. The area was measured to a constant point on South Beach as
shown by the line on Figure 32. The South Beach barrier island shoreline has also
retreated landward almost one island width as the inlet has evolved. Again the
preinlet area of the then Nauset Spit barrier was measured from the 1987 breach
to the limit line on the 1982 preinlet photo set. Figure 33 shows the measured
change in area and Figure 34 shows the change in estimated volume of the south
spit. The area and volume of this south spit reached a minimum in 1989 as the spit
moved rapidly south and west.
In 1990, the southward movement slowed and a more westward movement
began. With the welding of the spit to the mainland in 1992, the area and volume
has grown as sand has been deposited to the land bridge. The initial east-west
orientation of the land bridge has changed to a more northwest-southeast orienta-
tion as sand has accreted to the spit and the south ebb channel has migrated up
against this beach. This landform reached its maximum area and estimated vol-
ume in 1997/98 and is now slightly decreasing in area and volume as the beach
continues to experience overwash into the bay and landward retreat of the
shoreline.
South Flood Shoal
Prior to inlet formation, several shoals existed in Chatham Harbor. One of
these shoals, the south remnant shoal, was in front of the Chatham Lighthouse and
was oblong in shape (Figure 35). After the inlet breached the barrier spit, this
shoal became incorporated into the south flood shoal. Modified by tidal currents
and waves entering the bay through the inlet, this shoal migrated to the south and
was at times composed of from one to two segments separated by channels into
south Chatham Harbor. The south and westward migrating south spit finally
overtook the south shoal in 1991. The measured area (Figure 36) and estimated
volume (Figure 37) of the shoal remained constant until 1989 when the size
increased as sand was added to the shoal as it overtook the south remnant sand flat
to the south. The maximum volume was reached in 1990 as the shoal migrated
south between the mainland beach and south spit. Most of the south shoal was
incorporated into the south spit in 1991 and finally the spit welded with the main-
land and incorporated the south shoal into the continuous sand bridge connecting
the mainland with South Beach by early 1992.
Remnant South Sand Flat
Another preinlet shoal was located south of Chatham Lighthouse near a
marina entrance and the spit to Morris Island. Figure 38 shows the location of the
remnant south sand flat relative to the south remnant shoal/south flood shoal
52
Chapter 4 Ebb and Flood Shoal Evolution
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