Island south shoal, located adjacent to the mainland and Tern Island, changed
shape and orientation. Dredging became necessary to maintain a navigable
channel access to the Fish Pier and harbor area for Chatham's commercial fishing
fleet. Soon after establishment of the inlet, the mainland beach opposite the inlet
underwent severe erosion. Several homes were lost, as the mainland shoreline
directly across from the new opening retreated landward due to waves and tidal
currents impinging on the shoreline. Other areas of the mainland shoreline, both
updrift and downdrift of the inlet opening, experienced accretion as longshore
currents deposited the newly eroded sand in shore-attached shoals. This report
will identify this complex pattern of inlet morphology development, channel
migration and shoaling, and shoreline modification. Recommendations to
maintain navigation in this highly dynamic environment will be presented.
Project Setting
Chatham Harbor, is a bar-built estuary/lagoon located on the southeastern
corner of Cape Cod, MA (Figure 1). The estuary is an elongate, coast parallel
feature approximately 4 miles (6 km) long, 1.6 miles (1 km) wide and had a
maximum depth of 22 ft (7 m) prior to the breach. The estuary widens into the
more shallow Pleasant Bay on the north end.
Prior to the breach, the Chatham Harbor/Pleasant Bay estuary was sheltered
from the Atlantic Ocean by a 10-mile- (16-km-) long barrier spit called Nauset
Beach, which is attached to the mainland at the north end of Pleasant Bay. This
spit averaged 1,250 ft (381 m) wide and contained a sandy beach backed by
irregular sand dunes and a back-barrier marsh. The estuary opened to the ocean
through what was called Chatham Bars Inlet located between the southern end of
Nauset Spit and Monomoy Island. This inlet is now called the South Channel
(Figure 1). Monomoy Island was originally an 8-mile- (12.9-km-) long barrier
island to the south and west of Chatham Bars Inlet. Monomoy Island was itself
breached around 1978 and is now bisected by an unnamed inlet separating North
and South Monomoy Islands. The north end of Monomoy Island has been sepa-
rated from Morris Island by Morris Island Cut. When the new breach formed
during an extratropical northeaster on 2 January 1987, the barrier island formed
from the southern part of Nauset Spit became known as South Beach. From 1987
to 1992 the Chatham area of southeastern Cape Cod had a complex four-inlet,
estuary, and barrier island system.
Cyclic history of inlet system
Historically, this barrier system has an approximate 140-year cycle of barrier
spit growth and inlet formation (Giese 1988). The cycle starts with the growth of
Nauset Spit southward from the mainland sea cliffs of Eastham and Wellfleet. The
spit migrates southward with the prevailing longshore drift until a storm occurs
and a breach breaks through a weak point in the barrier, creating a shortened spit
and a detached barrier island from the southern portion of the spit. This southern
barrier continues to migrate to the south and west and eventually welds to the
mainland. Charts and other records dating back to the 1700s indicate that an inlet
2
Chapter 1 Introduction
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