Whether you live near an ocean beach or a lake, one thing they both have in common is sediment. Sediment is important to stabilize water plants, allow for infiltration of water, it serves as habitat for fish and other benthic or near shore communities, and is an ideal place to sit and take in the view. Beaches are not naturally stagnant though, and much like any other natural system, they prefer to meander. Because this is the case, and millions of people are now living near coastlines, many areas are willing to take drastic measures to ensure that the natural processes that move beaches do not affect their day-to-day lives. From jetties to sea walls, we will examine shoreline stabilization structures and the environmental impacts of each.
Beach Ecology and Management
Sand exists in many different habitats and arrives at the beach in a variety of ways. The two most common transport mediums of sand are rivers and eroding coastal bluffs (1,5). Once the sand has been delivered to the beach, it enters the littoral cell (5, 6). The littoral cell describes the total area from which sand enters the transport system (e.g. a river mouth) to where it meets its final destination (e.g. a deep sloping shelf.) Longshore drift, a type of current that moves parallel to the shore, will over time move sand from its point of entry, along the shoreline and eventually move it seaward(5). Beaches are created in this manner, and naturally over time have a preference to retreat towards land and narrow out, as nature shapes the landscape. Scientists will use this information to create a sediment or beach budget. By looking at the strength of currents of a particular area, intake of sediment and the amount of sediment lost, they can determine if a beach has a net gain or loss of sand to better determine stabilization measures that may be necessary(6).
A Growing Beach
A beach is considered growing if the amount of sediment entering the littoral cell exceeds the amount leaving it. While no beach can grow forever and wave energy is constantly moving sand around naturally, there are significant ways that humans are rapidly altering the littoral cells they live in and the beaches they call home. There are three major system failures contributing to beach loss: ocean acidification leading to loss of calcium carbonate containing shell fragments and sediments, coastal armoring and shoreline structures, and dammed rivers (5).
Shoreline Stabilization Structures
As people are more and more drawn to living on the shoreline, officials have had to come up with ways to prevent the natural landward movement of the beach. Most of the structures in place today keep high tide and strong waves from intruding on beachfront property, but fail to protect the beach or the animals that require it as part of their life cycle. In fact, in many cases the shoreline structures, such as seawalls and rip rap revetments, end up destroying beaches over time and increases the effects of sea level rise on coastal communities (4,7). Shoreline stabilization structures are not only largely ineffective at maintaining and facilitating beach growth but they are very costly. Each shoreline structure will cost the tax payers that need or request them thousands of dollars per linear foot in installation costs, permitting fees, upkeep and replacement each year (1,7).
Common Types of Shoreline Stabilization Structures
Seawalls are hard structures that run parallel to the water with the intent of physically blocking and absorbing wave energy from moving the sand. When the seawall is installed, there may be a healthy beach between the water and seawall. Over time, longshore drift will try to move the sand along the coast and eventually hit the seawall. The wave energy will bounce back and take with it sand from the beach (5). The result is erosion, prevention of landward movement of the beach, and in some case can prevent access to the beach for recreation. Seawalls can prevent some species, such as sea turtles, from reaching their natural breeding grounds and some studies have suggested that littoral cells with seawalls may only support half of the species diversity of their natural counterparts (1,3).With that being said, seawalls are beneficial to those that live on the waterfront. It will stop the inevitable slow movement of the ocean up to beachfront properties and helps protect communities during storm events. They are not fool-proof though and require homeowners and officials to be diligent in terms of maintenance, replacement and cost.
Breakwaters (Rip Rap)
Breakwaters are usually large piles of massive rocks designed to intercept wave energy for calmer waters and to keep sand in place. Typically, rip rap covers extensive areas of beaches that would normally be used by aquatic species to forage, take shelter and breed. In some situations, the increase in temperature and differences in types of rocks will influence intertidal communities and algae that will out compete with natural and preferred species (1). Rip rap can function similarly to a seawall where longshore drift will move sand and erode the beach. However, the rocks can hold on to and trap sand preventing it from being part of the sand transport system and eventually erode areas located down beach (5).
Both breakwaters and seawalls are hard structures that are intended to stop beach erosion in a single location, but without other structures in place, they will end up eroding surrounding beaches, even leaving nearby areas without the structures more susceptible to storms (2). Shoreline stabilization structures also make it harder for coastal zones to recuperate from strong storms by blocking sand and sediment from replenishing newly eroded shorelines (3). While these structures do protect coastal communities from high tide and storms now, sea level rise will eventually cause current shoreline stabilization structures to fall below the high tide line (1). This will result in a need for officials to examine new ways of dealing with coastal properties and retreating beaches.
Groins and Jetties
Groins and jetties are unlike breakwaters and seawalls, in that their purpose is not necessarily to stop the landward retreat of the beach, but rather to intercept longshore drift. A groin, much like a jetty, is built perpendicular to the beach and is built out of boulders, concrete or wood (5). While both groins and jetties want to stop longshore drift, they do so for very different reasons. Groins are built to stop the loss of sand and ultimately stop erosion of a particular beach. A groin will stop longshore drift and hold on to the sand that was being transported further down the beach so that it accumulates along the groin. In this way, the beach will “grow.” As this beach grows however, the beach further down shore will erode as longshore drift picks back up and has nothing to leave behind (5).
A jetty is built to retain an open channel to allow boats through an inlet. While their motives are different the product is the same. Jetties tend to be longer than groins and intercept more longshore drift and sand, and therefore grow larger beaches. This does create problems though as water circulation can be affected due to the size of the jetty or it becomes saturated with sand. If clogging occurs, the sand will have to be removed.(5).
Many coastal communities will utilize beach nourishment as a way to counteract the effects of beach erosion (1,5,7). This involves adding beach sand from somewhere else in an equal amount to that which was lost (1) There are several problems with this though as it is incredibly costly, needs to be replaced on average every four years depending on the wave energy and circulation patterns in the littoral cell, and can create a hazard to swimmers as the addition of sand causes the beach to move seaward rather than landward (1,5). This also poses problems for animals living in the sediments of the intertidal zone; the addition of extra sand can increase turbidity and cause animals to suffocate or become easy prey when disoriented in the sand (5).
Some communities are taking a more proactive approach though, with “soft” or “green” shoreline stabilization structures (7). This process includes removal of all or part of the hard structure (if there was one), increasing native vegetation, the use of anchored logs, and nourishment of sand and gravel. Many different strategies and tools can be used to employ soft stabilization. The goal is to increase the connection between land and sea and allow for a more natural ecological system to exist. In some instances groins may even be used to help encourage beach growth instead of replacing a seawall or rip rap (7).
Optimally, soft stabilization would strike a balance that allows for home and property owners along the coast to understand and want to care for the beach, instead of continually replacing hard structures that only serve to degrade the beach and coastal habitat. This is a relatively new concept and one that has individual application and meaning for each beach it is used on.
Shoreline stabilization structures are necessary as long as people are living on the waterfront. The beach naturally wants to retreat towards land and the interaction between land and sea is vital to ensure a healthy ecosystem. When structures are put in place to protect people and buildings, it removes the flow of nutrients from one system to the other, prevents proper healing after a storm, and keeps sea life from finding and utilizing their habitat. Soft stabilization structures strike a refreshing balance between the protection people need and ecological services animals and plants require. But at the end of the day, the best way to protect your home and heal the beach is to not build on it.
- Stamski, Rebecca. 2005. The impacts of coastal protection structures in California’s Monterey Bay National Marine Sanctuary. Marine Sanctuaries Conservation Series MSD-05-3. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Marine Sanctuaries Division, Silver Spring, MD. 18 pp.
- ‘Coastal Armoring and Policy Guidelines’. Bureau of Beaches and Coastal Systems Division of Water Resource Management. Section 161.085, Florida Statutes and Chapter 62B-33, Florida Administrative
- ‘Information About Sea Turtles: Threats from Coastal Armoring’ . Sea Turtle Conservancy. Accessed 07/01/2015. http://www.conserveturtles.org/seaturtleinformation.php?page=seawalls
- Griggs, Gary. ‘Shoreline Armoring.’ 05-13-2015. Accessed 07/01/2015. org
- ‘Shoreline Structures Why We Should Care.’ Beachapedia. 04/05/2014 Accessed 07/01/2015. http://beachapedia.org/Shoreline_Structures#Groins
- ‘Sediment Budget.’ Coastal Morphology Group, Scripps Institution of Oceanography. 06/25/2003. Accessed 07/01/2015. http://coastalchange.ucsd.edu/st3_basics/budgets.html
- Gianou, K. 2014. Soft Shoreline Stabilization: Shoreline Master Program Planning and Implementation Guidance. Shorelands and Environmental Assistance Program, Washington Department of Ecology, Olympia, WA. Publication no. 14-06-009.