continued to grow and migrate southward moving south another 2,000 ft (610 m).
Ebb shoal sediments were now off the northern end of South Beach. The main
ebb channel continued to move south but at a slower rate than earlier. The main
ebb channel was restricted in its southern movement by the land bridge and only
the distal end over the ebb shoal moved some 2,000 ft (610 m) further south. The
ebb shoal/swash platform complex also expanded into the bay.
The North Beach spit became more stationary as the main ebb channel moved
further to the south. The northward retreat has stopped as predicted by Liu et al.
(1993) based on the fact that the inlet throat had reached far enough south so that
the ebb tidal shoal no longer affects the spit or the nearshore bar system off the
end of Nauset Beach. The center line of the main ebb channel was approximately
5,500 ft (1,676 m) south of the north spit during this time period and the main
driving mechanism for north spit movement is related to the seaward reorientation
and displacement of the north beach nearshore bar system.
With the enlargement of the ebb shoal into the bay, the main ebb channel was
forced closer to the mainland beach. By 1995, a new north ebb channel had
established itself on an east-west orientation some 1,500 ft (457 m) south of the
north spit. It is suspected that the long narrow main ebb channel to the south had
become too restricted to carry the ebb flow out of the estuary and a new shorter,
more efficient, channel established itself closer to the main body of the estuary.
With the welding of the south spit to the mainland and the filling of the ebb shoal
across the throat of the inlet, the circulation patterns of the inlet underwent a
drastic change over these 3 years. The establishment of a northern ebb channel
bisected the swash platform and shortened the northern portion of the platform.
The central swash platform was large and had numerous swash bars and small
channels. Sediment transport pathways based on morphology from May 1995 are
shown in Figure 51. The flood flow into the inlet was accomplished both on the
north and central swash platforms. The flood shoal by this time developed a large
flood ramp and the main west flood channel was in the center of the ramp. The
expanding ebb shield deflected the return ebb flow from the upper parts of
Chatham Harbor and Pleasant Bay around both sides of the flood shoal. Since the
west channel was forced close to the mainland beach, tidal flow became restricted
through that channel. Two spillover lobes trying to form through the ebb shield
suggest that the ebb flow was having difficulties navigating the flood shoal and
was trying to establish a straighter route to the inlet throat.
Inlet Development (1995-1999)
With the closure of south Chatham Harbor and the establishment of the
second north ebb channel, Chatham Inlet continues to evolve toward a dynamic
equilibrium with the prevailing coastal processes. Net changes in the main ebb
channel, ebb shoal edge, north spit and South Beach land bridge for the third
period from 1995 to 1999 are shown in Figure 52. With the southern main ebb
channel extending some 6,000 ft (1,829 m) in length and being forced against the
mainland beach by the ever expanding ebb shoal, the flow through this channel is
much more restricted than before. Over this last 3-year period, the position and
orientation of this channel has remained relatively stable. The newer north
Chapter 5 Sediment Pathways