what are alternatives to hard stabilization? please select all that apply.
Why We Should Intendance
Seawalls, groins, jetties and other shoreline stabilization structures take had tremendous impacts on our nation'due south beaches. Shoreline structures are built to alter the furnishings of ocean waves, currents and sand movement. They are usually built to "protect" buildings that were built on a embankment that is losing sand. Sometimes they are built to redirect rivers and streams. Other times they are constructed to shelter boats in calm water. In many cases, seawalls, jetties, breakwaters and groins have caused down-coast erosion problems with associated costs that have greatly exceeded the construction toll of the structure.
Every surfrider knows that there are groins and jetties that take incidentally improved wave riding. Still, in many other areas shoreline structure has ruined wild animals habitat, destroyed surfing waves and caused beaches to erode. As embankment lovers and environmentalists, we need to understand the consequences of shoreline structures so that we may be able to effectively influence decisions on the impacts, placement or necessity of these structures. As an ecology grouping committed to maintaining the natural shoreline and beach equilibrium, we are usually opposed to structure that volition disrupt the balance of forces that shape our coastline.
The Nuts
Erosion: Where Has All The Sand Gone?
Every winter, the newspapers evidence pictures of oceanfront buildings falling into giant surf. Beaches are not static piles of sand. Ocean currents cause beaches to move constantly. Embankment sand is primarily a product of the weathering of the land (such equally natural erosion of littoral bluffs). Sand tin can also come up from sea organisms such as coral. Nevertheless, nigh of the sand along the earth's beaches comes from rivers and streams. When natural processes are interfered with, the natural supply of sand is interrupted and the beach changes shape or can disappear completely. Sand production stops when coral reefs die from pollution, when coastal bluffs are "armored" by sea walls and when rivers are dammed or channelized (lined with concrete) upstream for flood command and reservoir structure. The sand that collects behind upstream dams and reservoirs is often "mined" and sold for concrete production. Information technology then never makes it to the beach. A public resource essential for our beaches is instead sold for private turn a profit.
In the face of eroding beaches, owners of beachfront property will often try to use their political influence to demand that "something exist done." The intelligent activity would be to move the building away from the ocean. Unfortunately, what has often been done in the by has been to armor the coastline with rocks, concrete and steel. This does not protect or maintain the embankment - it only protects the buildings, temporarily.
Millions of taxpayer dollars have been wasted subsidizing beachfront edifice. Federal flood insurance and expensive Army Corps of Engineer projects accept done very little to make oceanfront buildings safe and have hastened beach erosion. In many cases, it would be more cost-effective for taxpayers to have the government buy the coastal property, condemn the buildings and allow the area to act every bit a buffer betwixt the ocean and the remaining buildings. In urbanized areas with expensive existent estate, a more price effective and environmentally sound culling to shoreline structures may exist to periodically "nourish" the beach with sand.
The Littoral Cell
On the W Declension of the U.S., beach sand moves from river mouths to the embankment. It then moves along the coast in the direction of prevailing currents and eventually it moves offshore. This sand transport arrangement is called a littoral cell.
When waves break at an bending to the shoreline, part of the wave's energy is directed along the shore. These "longshore currents" period parallel to the shore. Surfers telephone call this the "drift". This current volition motility sand along the shore and a beach will be formed. The same current that transports a surfer down the beach from the betoken of entry will also movement beach sand downwardly the shoreline. When this longshore current turns seaward, it is called a rip electric current.
Some areas have underwater canyons almost the embankment. These submarine canyons were prehistoric river mouths. Sometimes the longshore current volition exist interrupted by 1 of these canyons. In this example, the sand is lost from the beach in water too deep to exist returned to shore. The littoral jail cell system, from the river mouth to the underwater canyon, will always lose embankment sand. If the sand supply from the river is cutting off, the embankment will lose sand causing the beach to become narrower.
On the East Coast of the U.Due south., the shore formed differently. Sand comes from the erosion of headlands, bluffs and cliffs. The underwater coast (continental shelf) of the east is broad and flat. East Coast beaches are generally wider. Barrier islands run along the coast. In contrast to the Westward Coast, submarine canyons are rarely near the beach and seldom act every bit conduits for sand loss. A notable exception is the Hudson Canyon at the southwest end of Long Island, New York. Sand that moves south here is lost down the canyon. On the East Coast, sand "loss" is primarily from the movement of bulwark islands. Bulwark islands naturally migrate landward due to sea level rise, but this migration is accelerated during storm events. Powerful hurricanes deposit sand inland by washing it over the dunes. Sometimes these storms volition create strong currents that have sand too far offshore for it to return to the beach. The depth where sand is moved so far offshore that it cannot return is known as the "closure depth". The precise depth is nether scientific debate and varies with fourth dimension, wave and weather weather. When humans effort to interfere with the natural migration of barrier islands, it is usually at their long-term peril.
Erosion is a procedure, not a problem. Beaches are dynamic and natural. Buildings, bridges and roads are static. The problem occurs when at that place is a static structure built on a dynamic, moving embankment. If buildings and roads were not built close to the shore, nosotros would not have to worry about shoreline structures or sand erosion, as beaches would simply migrate inland.
Responses to Erosion
Seawalls
Meet the full article: Seawalls
When coastal buildings or roads are threatened, usually the first suggestion is to "harden" the declension with a seawall. Seawalls are structures congenital of physical, forest, steel or boulders that run parallel to the beach at the land/h2o interface. They may also exist called bulkheads or revetments. They are designed to protect structures past stopping the natural move of sand by the waves. If the walls are maintained they may hold back the sea temporarily. The construction of a seawall ordinarily displaces the open embankment that it is congenital upon. They also prevent the natural landward migration of an eroding beach.
See this gallery of photos of seawalls, revetments and other attempts at shoreline armoring from around the world.
When waves hit a smooth, solid seawall, the wave is reflected back towards the ocean. This can brand matters worse. The reflected wave (the aftermath) takes beach sand with it. Both the beach and the surf may disappear.
Seawalls tin cause increased erosion in adjacent areas of the beach that do not have seawalls. This so-chosen "flanking erosion" takes place at the ends of seawalls. Wave energy tin be reflected from a seawall sideways along the shore, causing coastal bluffs without protection to erode faster. When it is necessary to build a seawall, information technology should have a sloped (non vertical) face. Seawalls should besides take pockets and grooves in them that will use up the free energy of the waves instead of reflecting it.
Usually the most cost-constructive, environmental solution is to motion the building away from danger. Building seawalls volition purchase time against natural processes, but it volition not "solve the problem" of erosion by waves.
Groins
Groins are another example of a difficult shoreline structure designed as then-chosen "permanent solution" to beach erosion. A groin is a shoreline structure that is perpendicular to the beach. It is usually fabricated of big boulders, but it tin can be made of concrete, steel or wood. It is designed to interrupt and trap the longshore menses of sand. Sand builds up on one side of the groin (updrift accretion) at the expense of the other side (downdrift erosion). If the current direction is constant all year long, a groin "steals" sand that would normally be deposited on the downdrift end of the beach. The amount of sand on the embankment stays the same. A groin simply transfers erosion from one place to another further down the beach.
Groins occasionally ameliorate the shape of surfing waves by creating a rip current side by side to the rocks. The rip can exist a hazard to swimmers. The rip can likewise divert beach sand onto offshore sand bars, thereby accelerating erosion. Groins tin can too ruin the surf. If the waves are reflected off the rocks, the waves may lose their shape and "close-out."
As presently as one groin is built, property owners downdrift of it may start clamoring for the government to build groins to save "their" beach. Somewhen, the beach may get lined with groins. Since no new sand is added to the system, groins simply "steal" sand from ane part of the embankment and then that it will build upward on another role. In that location will always be beach erosion downdrift of the final groin.
Breakwaters
A breakwater is a big pile of rocks built parallel to the shore. It is designed to cake the waves and the surf. Some breakwaters are below the water's surface (a submerged breakwater). Breakwaters are usually built to provide calm waters for harbors and artificial marinas. Submerged breakwaters are congenital to reduce embankment erosion. These may also be referred to as artificial "reefs."
A breakwater can be offshore, underwater or connected to the country. Equally with groins and jetties, when the longshore current is interrupted, a breakwater volition dramatically modify the profile of the embankment. Over fourth dimension, sand will accumulate towards a breakwater. Downdrift sand will erode. A breakwater can crusade millions of dollars in beach erosion in the decades after it is congenital.
Beach Nourishment
In contempo years, the hard structures described in a higher place have fallen somewhat out of favor by communities due to the negative impacts we have discussed. Beach nourishment (or beach fill) is becoming the favored "soft" culling. Embankment nourishment is just depositing sand on the beach in gild to widen it. Although paid for by all taxpayers, it is frequently undertaken to protect private oceanfront buildings. Occasionally the taxpaying public is refused admission to beaches that they take paid to protect. Sand nourishment is a costly, temporary solution. The projects are not intended to have a long life span and must exist renourished on a regular basis, creating a cycle that will keep until the money runs out or shorefront buildings are relocated.
There are many considerations that must addressed when designing a nourishment project. If the grains of sand are not exactly the same size equally that of the natural embankment, the newly nourished beach may erode faster than the natural beach was eroding. Beach nourishment can cause bottom organisms and habitats to be smothered by "turbid" water that has sand and mud suspended in information technology. The shoreline is moved seaward into deeper water, causing the beach to drop off quickly, posing a take chances to swimmers. This may also impact the surf for a period of time, causing the waves to interruption as shore break, until the beach and sandbars can reestablish a level of equilibrium.
Harbors, Natural and Artificial
On the West Declension of the U.South., artificial harbors accept been constructed past edifice a series of breakwaters and jetties. When an artificial harbor is built in an expanse that is subject area to high-energy wave action, it volition invariably interrupt the longshore period of sand. This volition cause serious downdrift erosion. Some harbor designs forcefulness the longshore electric current to make a 90-caste turn towards the sea. This causes a large rip current that may bear sand offshore that might otherwise remain in the surf zone. This will take the effect of completely changing the shape of the ocean lesser. An artificial harbor mouth can human action every bit a trap for the longshore sand transport causing it to clog up with sand, which makes costly periodic dredging projects necessary.
Natural harbors, like San Francisco Bay, are protected from the body of water'due south fury but are all the same subject area to tidal and wave energy. This causes water mixing and circulation. Stagnant artificial harbors are easily polluted past boating activities: paint, oil, grease, garbage and illegally dumped sewage. These wastes can poison the living creatures that swim in these waters. When the harbor is dredged, the sand and contaminated sediments cannot exist returned to the beaches and must be disposed of in a safe identify. Often, the sediments are dumped in deeper waters, poisoning the marine life food web.
Some harbors accept been built by dredging wetland areas. Wetlands are habitat for birds and marine life. They can likewise provide h2o storage capacity to prevent coastal flooding during rains. Wetlands are natural h2o filters that purify land run-off before information technology enters the ocean. Dredging a wetland to build a gunkhole harbor should never exist done. We take lost over half the wetlands in the U.South. to human development. In California, we have lost over 94% of our wetlands.
Jetties
Jetties are large, human-made piles of boulders or concrete that are built on either side of a coastal inlet. Whereas groins are built to modify the furnishings of beach erosion, jetties are built and then that a channel to the sea will stay open up for navigation purposes. They are also congenital to prevent rivermouths and streams from meandering naturally.
Jetties completely interrupt or redirect the longshore current. Simply as a groin accumulates sand on the updrift side, then do jetties. The major difference is that jetties are usually longer than groins and therefore create larger updrift beaches at the expense of the smaller downdrift beaches.
On East Declension barrier islands, ocean tidal inlets migrate naturally with the longshore electric current. A jetty organization will permanently disrupt the equilibrium of the beach. This may seriously affect the tidal circulation and the health of the wetlands between the bulwark islands and the mainland.
Inlets with short jetties that don't quite reach the surf will clog upwards with sand. The sand must exist dredged on a regular ground. A "sand by-passing" organization may be congenital to pump sand around the jetties. The sand pumping may come from within the inlet or from the updrift beach. These methods are expensive and must exist maintained indefinitely.
What Yous Can Practice
Ecology Impacts
Before a shoreline structure is built, the local community must exist informed of its environmental impacts. The National Environmental Protection Human action (NEPA) mandates that an Ecology Impact Statement (EIS) must be prepared to identify environmental impacts of the project. This document must spell out all effects that a new structure will have on the surrounding expanse. It is during the scoping of and subsequent public comment catamenia of preparing an EIS that Surfrider Foundation activists can have the greatest impact on the proposed project.
The EIS procedure allows activists to educate the public about the project's impacts on the environs. Written comments on the draft EIS are crucial for legal purposes. Oral comments at hearings are even more important considering they are picked up in the media, which allows more of the public to go informed.
Our goal is to brand certain that the long-term furnishings and the truthful costs of the project are carefully spelled out for both the public and the determination-makers. If there are environmental impacts, the developer must provide ways to "mitigate" the damage. For instance, if the project volition cause downcoast erosion, the programmer may be required to install and maintain a sand replenishment system or hope to post a bond that volition pay for periodic sand replenishment as long every bit the structure exists. This may exist impractical. If in that location is wild animals habitat destroyed, the programmer may be required to restore habitat on site if feasible.
The But Permanent Solution: Retreat from the Beach!
"Difficult" shoreline structures have astringent environmental impacts on the longshore current and the natural processes of beach sand distribution. "Soft" solutions like sand nourishment are expensive and temporary. Marinas should be congenital in natural harbors away from the energy of the waves. Building on our sea's shore is not a expert idea. NATURE WILL ALWAYS PREVAIL.
Shoreline construction means that taxpayers pay the bills when the ocean behaves equally expected. Whether information technology is fire department rescues, the Public Works Section placing sand bags, the constabulary guarding vacant buildings from looters or the Army Corps of Engineers spending millions to "correct the problem," taxpayers are the ones who pay. Shoreline protection is, often, "welfare for the rich."
Shoreline belongings owners often limit the public's access to the embankment by refusing to let the public cantankerous their holding to get to the beach.
Shoreline building also means habitat devastation. Birds, plants and animals that call coastal dunes and beaches their homes are slowly becoming extinct.
Every bit humans continue to overpopulate our littoral areas (and the planet) we will take to be more than thoughtful about our relationship with the ocean. Surfrider Foundation activists will continue to educate the public about the natural processes that create and maintain our shoreline. Sometimes shoreline structures must exist congenital, but the public must know the impacts. Society will have to continually pay to maintain the structures and correct the environmental impairment caused by them. The all-time solution is to retreat from the embankment and allow nature to furnish, maintain and alter the beach as she sees fit.
Surfrider Foundation Beach Preservation Policy
Restore the Shore Video
Video produced past the San Diego Chapter of Surfrider Foundation discussing beach erosion, shoreline structures and ways to respond to the changing coast.
N Carolina'due south Summary of the Furnishings of Shoreline Structures
Since 1985, Due north Carolina prohibited shoreline armoring. The following text, from the country's 2010 Habitat Protection Plan does a expert job explaining the concrete and ecological effects of shoreline armoring:
"Shoreline hardening, or hard stabilization, involves construction of hard immovable engineered structures, such equally seawalls, rock revetments, jetties, and groins. Seawalls and rock revetments run parallel to the embankment. Seawalls are vertical structures, constructed parallel to the ocean shoreline, and are primarily designed to prevent erosion and other harm due to wave activeness. Revetments are shoreline structures constructed parallel to the shoreline and generally sloped in such a mode equally to mimic the natural slope of the shoreline profile and misemploy wave energy every bit the wave is directed up the slope. Breakwaters are structures constructed waterward of, and unremarkably parallel to, the shoreline. They attempt to pause incoming waves before they achieve the shoreline, or a facility (e.g., marina) being protected. Jetties and groins are manmade structures constructed perpendicular to the beach, with jetties usually existence much longer, and are located side by side to inlets with the purpose of maintaining navigation in the inlet by preventing sand from entering information technology. In contrast, terminal groins are structures built at the end of a littoral cell to trap and conserve sand along the end of the barrier island, stabilize inlet migration, and widen a portion of the updrift beach. Terminal groins are designed so that when the expanse behind the groin fills in with sand, boosted sand will go around the structure and enter the inlet system.
It is well accepted that hard stabilization techniques along high energy ocean shorelines will advance erosion in some location forth the shore as a result of the longshore sediment transport being altered (Defeo et al. 2009). The hydromodifications resulting from littoral armoring modifies sediment grain size, increases turbidity in the surf zone, narrows and steepens beaches, and results in reduced intertidal habitat and multifariousness and abundance of macroinvertebrates (Walton and Sensabaugh 1979; NRC 1995; Dolan et al. 2004: 2006; Pilkey et al. 1998; Peterson et al. 2000a; Miles et al. 2001; Dugan et al. 2008; Walker et al. 2008; Riggs and Ames 2009). A study looking at the effect of a short groin (95m) on the benthic community found that the groin created a depositional condition on one side of the structure and erosion on the other, and macroinvertebrate diversity and abundance was significantly reduced within 30m of the structure, as sand particle size and steepness increased (Walker et al. 2008). The alter in benthic community was attributed to the change in geomorphology of the beach. Hard structures along a sandy beach can likewise event in establishment of invasive epibenthic organisms (Chapman and Bulleri 2003). A secondary touch of hardened structures is that the areal loss of embankment resulting from hardening of shorelines is oft managed past implementing nourishment projects, perhaps having additional damage to subtidal bottom (Riggs et al. 2009). Anchoring inlets likewise prevents shoal formation and diminishes ebb tidal deltas, which are important foraging grounds for many fish species. Recognizing that hardened structures are damaging to recreational beaches and the intertidal zone, four states have prohibited shoreline armoring: Maine, Rhode Island, Due south Carolina, and North Carolina (effective in North Carolina since 1985).
Mayhap the greatest impact of terminal groins and jetties results in the long-term effect on barrier islands and the effect that will accept on marine and estuarine ecosystems. By stabilizing the inlet, inlet migration and overwash processes are interrupted, causing a cascade of other effects (Riggs and Ames 2009). In the instance of Oregon Inlet, the final groin anchored the bridge to Pea Isle and stopped the migration of the inlet on the due south side. But the continuing migration of the north stop of Bodie Island led to an increased demand for inlet dredging. The combination of reduced longshore ship of sediment due to the groin and the mail-storm dune structure to open and protect the highway prevented overwash processes that permit Pea Island to maintain its tiptop over fourth dimension. With overwash processes disrupted, the beach profile has steepened, and the isle has flattened and narrowed, increasing vulnerability to storm damage (Dolan et al. 2006; Riggs and Ames 2009; Riggs et al. 2009). At Oregon Inlet and Pea Isle, the accelerated demand for beach replenishment is farther aggravated by the need to maintain Hwy 12 on the narrowing beach. From 1983 to 2009 approximately 12.vii million cubic yards of sand have been added to the shoreline within three miles of the terminal groin (Riggs and Ames 2009). Dolan (2006) documented that the large volumes of sand replenishment in this area, required to maintain the channel, protect the route, and maintain a beach take resulted in a pregnant reduction in grain size and reduction in mole crab abundance. Mole crabs are considered an important indicator of beach conditions due to their importance in the food spider web equally prey for shorebirds and surf fish. In addition to causing erosion on downdrift beaches, altering barrier island migration processes, and accelerating the need for beach nourishment projects, jetties obstruct larval fish passage through adjacent inlets (Blanton et al. 1999)."
This article is part of a series on Shoreline Structures looking at types of structures commonly built along shorelines, and the policies, laws, and regulations which tin affect where and under what conditions they are congenital.
For data nigh laws, policies and conditions impacting shoreline structures in a specific state, please visit Surfrider's State of the Embankment report to discover the State Report for that state, and click on the "Shoreline Structures" indicator link.
Source: https://beachapedia.org/Shoreline_Structures
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