PHYSICAL THERAPY

The Need to Intervene

Some beaches need physical intervention to deal with problems, such as storm impact or beach erosion. There are three major approaches of dealing with long-term beach erosion–beach nourishment being the preferred treatment by most coastal communities.

Beach erosion is a national problem as 80 to 90 percent of sandy beaches are currently eroding at rates of only a few inches to over 50 feet per year along the outer coastline of Louisiana, the erosion “hot spot” of the United States. Our knowledge of the causes and rates of erosion have greatly improved in recent years, and it is clear that rising sea level results in the long-term trend of landward shoreline movement. Coastal storms, including hurricanes, nor’easters and El Nino events, cause episodic changes in beach position and width. Oceanic beaches have a cyclic behavior–narrowing in the winter and widening in the summer in response to changes in wave activity. This seasonal fluctuation in beach dimensions is well understood by people who live or regularly visit beaches. Others are astounded (and dismayed) to find the beach in front of their home eroding severely or even disappearing in the wintertime, especially during very stormy years. Large coastal storms can overtop and flatten sand dunes, causing major damage to beachfront houses and infrastructure, such as roads and utilities. It is at this time that the public becomes aroused and calls for governmental action are made.

Sand is a valuable commodity and can be considered as a part of the necessary infrastructure of coastal communities. As the beach goes, so goes the local economy because the sandy beach is the draw for tourism. A wide beach serves both as a storm buffer to protect shorefront properties and also as recreational space. Long-term changes in shoreline position and beach width have been studied for many coastal areas, which permits better prediction of future changes. The average long-term erosion rate along the U. S. East Coast is 2 to 3 feet per year, but some areas are stable to slightly accretional while others are eroding at much higher rates. The Cape Hatteras Lighthouse on the Outer Banks of North Carolina was moved in the summer of 1999 because of a long-term trend of coastal erosion that amounted to a loss of 1,500 feet during the last century-a very high rate of sustained beach erosion.

Beach erosion can occur because of simple inundation of the land, but it largely involves the actual removal of sand from the beach to deeper water offshore or movement alongshore into inlets, tidal shoals, and bays. The relative rate of sea-level rise along the U. S. coasts has been approximately 1 foot in the last century with much higher rates along the Louisiana coast because of rapid land subsidence. A unit vertical rise in sea level translates into 150 to 200 units of horizontal retreat of sandy shorelines. While sea level rise sets the conditions for landward displacement of the shore, coastal storms supply the energy to do the “geologic work” by moving the sand off and along the beach. Therefore, beaches are greatly influenced by the frequency and magnitude of storms along a particular shoreline. The rate of sea-level rise is expected to accelerate in the coming decades in response to global warming, which would exacerbate existing erosion problems.

The management options available to control coastal erosion and protect beachfront properties include retreat, shore hardening, and beach nourishment. Retreat from the shore generally occurs in the aftermath of a major storm when beachfront properties have been heavily damaged or completely destroyed and the building lot has been greatly diminished or disappeared completely. Along the Outer Banks of North Carolina, coastal retreat has been the principal response to beach erosion and storm impact. Houses on the edge are often moved landward before being destroyed by waves and surges during coastal storms. The State of Texas has an Open Beaches Act that dictates that any house standing on the beach, even if it survived the storm, must be moved off the public property. Elsewhere, houses elevated on pilings that survived the storm surge are condemned by the health department because of the exposure of septic tanks on the beach. The retreat option is extremely unpopular with local residents because everyone wants to live on the beach, and the land is the generally much more valuable than the house itself.

Beachfront homeowners faced with erosional problems and possible storm damage often resort to shore hardening, especially bulkheads, in order to protect their invesment where permitted by governmental agencies. Shore hardening refers to the construction of a range of structures built to retain sand, interfere with waves and currents in order to reduce their damaging effects, or protect property from direct wave attack and hold back tidal waters. These structures built of wood, stone, concrete, or steel include bulkheads, seawalls, revetments, groins, jetties, and breakwaters (see Beach Glossary). Bulkheads and seawalls can protect upland property from damaging storm waves, but they do nothing to abate the erosion of the beach fronting the structure. In fact, such hard shore-parallel structures such as bulkheads and seawalls may accelerate beach erosion by reflecting wave energy off the facing wall, impacting adjacent property owners as well. Building such structures along retreating shorelines eventually result in diminished beach width and even loss. Groins and jetties intercept the alongshore movement of sand, building wide beaches on the updrift side and causing accelerated erosion of downdrift beaches. These shore-perpendicular structures do not create any new sand, but merely rearrange the sand that is on the beach. Groins are most effective and not detrimental when built as a cluster or “field” along a stretch of shoreline at the terminus of the alongshore movement of sand, such as at a harbor mouth. Offshore breakwaters have had mixed success, but there has been much less testing of this technology along U. S. beaches.

Beach nourishment is the process of adding new sand to the beach profile in order to restore it to some former width. This is usually accomplished by dredge and fill operations with sand pumped onto the beach from an offshore source, such as sand bars or shoals. Beach nourishment is only feasible at the community level as large sectors (e.g., miles of the shore) must be nourished to be economical viable. In the early 1980s, Miami Beach was restored at the cost of $65 million along this 10-mile strand of shore. While the cost was high, South Beach was rejuvenated, and today it is the “hottest” beach in the country; this beach nourishment project has paid for itself many times over. Where the rate of erosion is high or there are nearby sand sinks, beach nourishment projects have been much less successful-it is not a panacea for all coastal communities. Beach nourishment does not stop the erosion trend–it simply “resets the clock.” But beach fills achieve both goals of providing a wide recreational beach and reasonable storm protection for beachfront development. Where coral reefs are present, such as along South Florida and Hawaii, care must be taken because of the potentially damaging impacts of both the dredging process and the placement of sand, which can smother nearshore habitats and feeding areas for fish and sea turtles.

A coastal engineering project that is successful in one area may not be well suited for another shore. Beaches are a part and parcel of the quality of life in coastal communities, and efforts should be made to preserve these vital resources.