National Erosion Control Development and Demonstration
Program (Section 227)
River Street Cut, Seabrook, NH
Description
The town of Seabrook is located on the coast of New Hampshire, just north of the New
Hampshire-Massachusetts border. Hampton/Seabrook Harbor is characterized by a major
tidal inlet, large shoals
(including a flood-tidal delta),
and three major tributaries:
the Hampton and Taylor
Rivers to the north and the
Blackwater River to the
south. Historical aerial photo-
graphs show the estuarine
shoals and tidal channels
frequently shift position. To
reduce this shifting, the
U.S. Army Corps of Engi-
neers constructed a 1,126-
km- (700-mile-) long
entrance channel to the
harbor in 1965. The state
dredged the harbor in 1955,
View of Hampton/Seabrook Harbor
and since that time it has
remained an active, working
harbor.
Issue
The Blackwater River is changing course resulting in localized bank and bar erosion and
channel and harbor shoaling. The immediate problem is an erosion cut in the flood-tidal
shoal along River Street and the resulting shoaling at the Seabrook piers and mooring field.
A second area of erosion is also located in this flood-tidal shoal but is just north of the
Yankee Fisherman's Coop. This shoal is known locally as the "middle ground" and
contains New Hampshire's largest clam resource. This second point of erosion and
shoaling is of concern because of its strategic location at the mouth of the harbor.
Increased shoaling here could close the harbor. The increasing erosion has required more
frequent dredging in the harbor and mouth of the Blackwater River. While the harbor used
to be dredged every 5 to 6 years, it must now be dredged annually.
Technology
The general project concept is to abate the erosion along River Street and to minimize
shoaling of the inner harbor by filling the cut with dredged material and containing this fill
with two rows of thermoplastic-composite sheet pile. Thermoplastic composites are fiber
reinforced and are a recent, high-performance, advance in engineering materials. The
can be reinforced with glass, carbon and aramid fibers. These materials, particularly in the
form of sheet pile, have rarely been used in the marine environment and are expected to be
1
Commonly used abbreviation for polyetheretherketone
U.S. Army Engineer Research and Development Center
May 2005
www.erdc.usace.army.mil
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