Shore Protection: Part Soft, Part Hard

6.1.1.3 Hybrid Apppproaches to Shore Protection

Several techniques are hybrids of shoreline armoring and the softer approaches to shore protection. Often, the goal of these approaches is to retain some of the storm-resistance of a hard structure, while also maintaining some of the features of natural shorelines.

Groins are hard structures perpendicular to the shore extending from the beach into the water, usually made of large rocks, wood, or concrete (see Figure 6.7b). Their primary effect is to diminish forces that transport sand along the shore. Their protective effect is often at the expense of increased erosion farther down along the shore; so they are most useful where an area requiring protection is updrift from an area where shore erosion is more acceptable. Jetties are similar structures intended to guard a harbor entrance, but they often act as a groin, causing large erosion on one side of the inlet and accretion on the other side.

Breakwaters are hard structures placed offshore, generally parallel to the shore (see Figure 6.7a). They can mitigate shore erosion by preventing large waves from striking the shore. Like groins, breakwaters often slow the transport of sand along the shore and thereby increase erosion of shores adjacent to the area protected by the breakwaters.

Dynamic revetments (also known as cobble beaches) are a hybrid of beach nourishment and hard structures, in which an eroding mud or sand beach in an area with a light wave climate is converted to a cobble or pebble beach (see Figure 6.7d). The cobbles are heavy enough to resist erosion, yet small enough to create a type of beach environment (USACE, 1998; Komar, 2007; Allan et al., 2005).

Recently, several state agencies, scientists, environmental organizations, and property owners have become interested in measures designed to reduce erosion along estuarine shores, while preserving more habitat than bulkheads and revetments (see Box 6.3). “Living Shorelines” are shoreline management options that allow for natural coastal processes to remain through the strategic placement of plants, stone, sand fill, and other structural and organic materials. They often rely on native plants, sometimes supplemented with groins, breakwaters, stone sills, or biologs2 to reduce wave energy, trap sediment, and filter runoff, while maintaining (or increasing) beach or wetland habitat (NRC, 2007). (A sill is a hard structure placed along the edge of a marsh to reduce wave erosion of the marsh. A biolog is an assemblage of woody, organic, biodegradable material in a log-shaped form.)

In addition to the hybrid techniques, communities often use a combination of shoreline armoring and elevation. Many barrier island communities apply beach nourishment on the ocean side, while armoring the bay side. Ocean shore protection projects in urban areas sometimes include both beach nourishment and a seawall to provide a final line of defense if the beach erodes during a storm. Beach nourishment projects along estuaries often include breakwaters to reduce wave erosion (Figure 6.7a), or a terminal groin to keep the sand within the area meant to be nourished (see Figure 6.7c).

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Shore Protection: Part Soft, Part Hard

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6.1.1.3 Hybrid Apppproaches to Shore Protection

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