EM 1110-2-1100 (Part V)
31 Jul 2003
(a) Notched groins have recently undergone laboratory and field testing by the USACE (Kraus 1999;1
Kraus 2000). Trial notched groins have been implemented by the U.S. Army Engineer District, New York,
and the U.S. Army Engineer District, Philadelphia, along the south shore of New Jersey. The purpose of
notching is to bypass beach fill and littoral sediment so that the fillet and erosive response of the shoreline
are smoothed out, i.e., to straighten the shoreline adjacent to the groin. The goal is shoreline readjustment
to approach a smooth, continuous shoreline through a groin field. The efficiency of notching was defined
as the amount of sediment that passes the groin system, but that remains on the subaerial beach. Tentative
conclusions based on both the laboratory and field experiments are: notches in the swash zone are most
efficient; notches in the surf zone are less efficient and can have strong longshore currents, and be hazardous
to swimmers; surf zone notches may move sediment further from shore; notching a groin in the swash zone
may not be successful depending on how and at what rate sediment typically moves alongshore on the subject
beach.
(b) Spur groins are short, stub groins constructed at right angles to navigation jetties and the end groins
of groin fields to redirect currents and sediment transports. Sorensen (1990) describes a spur jetty constructed
as an emergency measure on the leeward side of two curved jetties to prevent a breach at the landward end.
Anderson, Hardaway, and Gunn (1983) document eleven locations in the Chesapeake Bay where short, shore
parallel groins are attached to the terminal groin near the beach. Over 12 years of beach response at one site
reveals that the spur groins cause diffraction and refraction effects to prevent the detachment of the terminal
groin at its landward end.
(c) Another way to smooth the shoreline is to make the groin more permeable as illustrated in
Figure V-3-34. A patented, concrete pile, permeable groin field has existed on Cayman Kai, Caribbean Sea,
for over 10 years and has survived many hurricanes (from Kraus and Bocamazo 2000). Environmental
restrictions against hardened shorelines in North Carolina has resulted in a groin field constructed from
geotextile materials filled with sand on Bald Head Island, North Carolina (Denison 1998). In theory, these
structures will provide sand for shore protection if they are damaged or fail in major storm events. Other
revisited or fresh concepts for groin designs listed in Table V-3-9 have only been proposed conceptually and
have yet to be field tested. These new and innovative approaches to groin design benefit from experience and
modern understanding of coastal sediment processes.
(6) Basic rules for functional design of groins. Ten modern rules for groins design can be summarized
as follows:
Rule 1
If cross-shore sediment transport processes are dominant, consider nearshore breakwater
systems first.
Rule 2
Conservation of mass for transport of sediment alongshore and cross-shore means groins
neither create nor destroy sediment.
Rule 3
To avoid erosion of adjacent beaches, always include a beach fill in the design
Agree on the minimum, dry beach width, Ymin. for upland protection during storm events
Rule 4
as a measured to judge success.
1
Kraus, N. C. 1999. "Completion of Notched Groin Research and Summary of Key Applied Findings," Memorandum for
Record, Coastal and Hydraulics laboratory, U.S. Army Engineer Research and Development Center, Vicksburg, MS.
V-3-76
Shore Protection Projects
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