Additional inlet evolution from October 1988 to December 1988 (described
in detail in Liu et al. 1993) showed an ever widening inlet throat and continued
recurving of the north and south barrier spits. By 23 May 1989, the south spit
breached again and that sand was deposited on the south flood shoal, limiting
navigation to the south Chatham Harbor (Figure 8). By this time, the south flood
shoal had migrated far enough south to merge with the south remnant sand flat.
The main ebb channel continued to migrate southward with the prevailing coastal
processes expanding the swash platform and expanding the ebb shoal seaward and
to the south. The west channel around the flood shoal into Chatham Harbor was
still the predominant channel, but navigation into the Fish Pier became more
difficult as the Tern Island Channel narrowed and moved more east-west. The
general trend was for the north flood shoal to migrate northward and expand in
area. Erosion still continued on the mainland beach, as sand was eroded from in
front of the inlet and moved to the north and south mainland beach area just past
the expanding inlet opening.
By December 1989, almost two years after inlet formation, the inlet main ebb
channel continued to migrate south. A large spit extended westward from South
Beach overtaking most of the south flood shoal. At this time a large stone revet-
ment type seawall was being constructed along the most severely eroded section
of mainland beach. By 15 August 1990, the South Beach sand spit almost
extended across the south Chatham Harbor (Figure 9). Navigation to the south
within Chatham Harbor was limited to only small craft through a small channel
that still existed adjacent to the mainland through the south flood shoal/south rem-
nant sand flat. The swash platform was becoming very large with development of
complex sand waves. The main west flood channel was now close to the recently
constructed mainland seawall. The ebb lobe in the west channel was more elon-
gate and presented less obstruction to navigation, and formed a linear shoal in
front of the seawall, with a spit extending south toward the ebb channel. Shoaling
became more of a problem at the entrance to the Tern Island Channel to the Fish
Pier as that channel reoriented more to the east.
In the February 1991 photo mosaic, the inlet configuration was basically the
same as in August 1990. By 31 December 1991, almost exactly 6 years after the
initial breach, the South Beach spit had continued to enlarge as the seaward tip of
the island became more rounded (Figure 10). There was still a small, shallow
opening to South Chatham Harbor, as the south flood shoal moved south more
into the harbor. The ebb shoal/swash platform, main ebb channel complex contin-
ued to grow to the south, with the orientation of the main ebb channel more to the
southeast. Nauset Beach Spit was now recurving less into the harbor but more to
the southeast. This north swash platform was also extending into the harbor
creating a very narrow opening for the main navigation channel between it and the
mainland beach. The north flood shoal expanded to the northwest, moving the
dominant west navigation channel closer to Tern Island. The Tern Island channel
rotated from a east-west orientation to a more northwest-southeast one, with a
wider channel. Erosion on the mainland beach progressed south past the Chatham
Lighthouse.
19
Chapter 3 Inlet Throat, Shoreline, and Channel Evolution
Previous Page
