Bulkheads and seawalls are man-made structures designed to protect bluffs and land banks by separating water and land. Bulkheads serve as retaining walls that keep earth and sand from slumping and crumbling. Seawalls, as the name implies, are used to resist wave action. According to the U.S. Army Corps of Engineers, both are most effective when used in areas where fishing and boating are the primary uses for the shore. Neither bulkheads nor seawalls are recommended for locations with gently sloping areas used for sunbathing and shallow-water swimming.
Seawalls usually consist of a vertical or sloping wall that is thick, sturdy and self-contained. In contrast to heavy seawalls, bulkheads are often comprised of relatively thin walls. Materials used in the construction of bulkheads and seawalls include treated timber, steel, vinyl, plastic, lean concrete and riprap, loose stones placed together to form a barrier. Today's high-performance bulkhead and seawall materials are designed to withstand the battering of waves and wave-carried debris while also being low-maintenance and eco-friendly.
Bulkheads and seawalls can be built in three types of design: thin, interlocking sheet piles placed deep into the ground; individual piles that support an above-ground structure; or a large gravity construction that rests on the shore bottom, or slightly in it, and is supported by its own weight instead of by piling. Timber, steel and aluminum are the preferred materials for sheet piles; concrete is preferable for gravity structures.
A bulkhead or seawall must be tall enough to prevent waves from lapping over the top of the structure; insufficient height could result in waves overtopping the structure and eroding the land. In addition, groundwater and rain percolating through soil can cause pressure that could eventually topple a bulkhead or seawall. To ensure that a water-retaining structure remains upright, weep holes should be placed along the bottom of it to relieve built-up water pressure.
If used in areas where significant wave action is present, bulkheads and seawalls could accelerate beach erosion rather than hinder it. When waves encounter a water-retaining structure, a significant amount of the wave's energy is directed downward to the area where the wall and soft sand or earth meet. As a result, the shore on the retaining side of the bulkhead or seawall is subjected to a significant amount of water force, which can cause the land to erode more quickly than if there were no wall.