Barrier island and mainland wet/dry line shoreline positions, channel center
lines and shoal areas were then digitized from the aerial images on the screen and
entered into the Geographic Information System (GIS) theme layer for each year.
There has been a great deal of change in the inlet system. Figure 3a identifies the
morphologic features associated with Chatham Harbor in the early years of forma-
tion circa 1988 when the South Beach was still detached from the mainland. An
example of the prominent morphologic features after the South Beach became
welded onto the mainland are shown in Figure 3b from the 1999 photographic set.
Details of yearly change will be presented in the next chapter.
Shoreline
Maps have been produced of the north Nauset Spit and South Beach ocean
and bay shoreline, and the Chatham mainland shoreline. The shoreline was
defined visually on the aerial mosaic as the wet/dry line on the beach, based on
the variation in color between the lighter gray tones of the dry beach and the
darker gray tones of the more saturated intertidal area. This has been interpreted
by some as the high-water shoreline but in reality would be slightly below the
actual debris line of maximum runup, which was not visible on most of the
photos. Since most of the photos were taken at or around low tide and the same
procedure was done on each date, this interpreted shoreline is thought to be a
good representation of shoreline change. Each shoreline was stored by date in a
separate layer.
Channel Center Line
Channels through the various shoals at Chatham Inlet were readily visible on
all of the photographs as darker areas between lighter sand deposits. The approxi-
mate center line was digitized as a line feature by visual inspection. The main ebb
channel through the ebb shoal was the most prominent channel feature. The pre-
inlet 1982 and postinlet 1987 to 1991 had a south Chatham Harbor channel that
connected the present opening with the Chatham Bars Inlet and Morris Island Cut.
As the north flood shoal evolved, the channels associated with this shoal also
changed, evolving from a west and east flood channel around the flood shoal to a
channel that was discontinuous through the center of the flood shoal. The entrance
channel to the Fish Pier has also evolved with this changing north flood shoal
morphology. The channel center lines for each year were placed on a different
layer.
Shoals
Several shoals have been identified as the inlet has evolved and the number of
shoals has changed as sediment has eroded and accreted with time. The outline of
each shoal was digitized using the intertidal and subtidal boundary based on color
change and bed forms visible on the photos. Water clarity is for the most part,
good in this area, so the interface between the lighter color, shallow shoal and the
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Chapter 2 Methods