EM 1110-2-1100 (Part V)
31 Jul 2003
Figure V-3-14. Definition sketch, headland breakwaters
(4) Applications on Chesapeake Bay. Headland breakwater systems have been built along the shoreline
of the Chesapeake Bay for shore protection and to maintain recreational beaches. Since 1985, 60 breakwaters
at 19 sites have been designed, constructed, monitored and analyzed to learn about their functional
performance (Hardaway, Thomas, and Li 1991; Hardaway, Gunn, and Reynolds 1995; Hardaway and Gunn
1991, 1995, 1998, 1999). The design method employs a three-step procedure that accounts for bimodal
annual wave climates (annual and storm wave direction) a numerical wave transformation model for near-
shore wave refraction and shoaling, and the beach planform shape model for static equilibrium (Silverster and
Hsu 1993). System design also includes upland runoff, bank geology, shoreline morphology, sedimentation,
and aesthetics. Potential impacts to adjacent shorelines must also be considered and minimized.
Figure V-3-15a displays before and after photos for the Van Dyke project on the James River. The dark area
along the shore is vegetation after the new bank was graded to provide sand for beach nourishment as part
of the construction. Figure V-3-15b displays 12 nearshore breakwaters at the Luter project site (James River)
one year after construction. Note the use of Y-shaped breakwaters to refine the shape of the planform beach.
Moving the breakwater ends further offshore changes the diffraction point to provide the desired planform
beach shape. Short breakwaters at both ends pin the downdrift beach. Experience since 1991 indicates that
on the Chesapeake Bay, the ratio of Yg/Lg is about 1.7 for stable, equilibrium-shaped beaches. As illustrated
in Figure V-3-16, at the Murphy project site (Potomac River) the present shore is still eroding and will require
several years to reach the predicted embayment shoreline shape. Hardaway, Thomas, and Li 1991 present
minimum design parameters for medium wave energy shorelines (average fetch 1-5 nautical
Shore Protection Projects
V-3-41
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