A groyne (in the U.S. groin ) is a rigid hydraulic structure built perpendicularly from an ocean shore (in coastal engineering ) or a river bank, interrupting water flow and limiting the movement of sediment . It is usually made out of wood, concrete, or stone. In the ocean, groynes create beaches , prevent beach erosion caused by longshore drift where this is the dominant process and facilitate beach nourishment . There is also often cross-shore movement which if longer than the groyne will limit its effectiveness. In a river, groynes slow down the process of erosion and prevent ice-jamming , which in turn aids navigation.
50-431: All of a groyne may be underwater, in which case it is a submerged groyne . They are often used in tandem with seawalls and other coastal engineering features. Groynes, however, may cause a shoreline to be perceived as unnatural. Groynes are generally straight but could be of various plan view shapes, permeable or impermeable, built from various materials such as wood, sand, stone rubble, or gabion , etc. The term groyne
100-491: A false sense of security to property owners and local residents as evident in this situation. Seawalls along the Japanese coast have also been criticized for cutting settlements off from the sea, making beaches unusable, presenting an eyesore, disturbing wildlife, and being unnecessary. After 2012's Hurricane Sandy , New York City Mayor Bill de Blasio invested $ 3,000,000,000 in a hurricane restoration fund, with part of
150-518: A high tide combined with a storm surge) may flow past the landward end and erode a channel bypassing the groyne, a process known as flanking . River groynes ( spur dykes , wing dykes, or wing dams ) are often constructed nearly perpendicular to the riverbanks, beginning at a riverbank with a root and ending at the regulation line with a head. They maintain a channel to prevent ice jamming, and more generally improve navigation and control over lateral erosion, that would form from meanders . Groynes have
200-528: A major impact on the river morphology : they cause autonomous degradation of the river. They are also used around bridges to prevent bridge scour . Groynes can be distinguished by how they are constructed, whether they are submerged, their effect on stream flow or by shape. Groynes can be built with different planview shapes. Some examples include straight groynes, hockey stick or curved, inverted hockey stick groynes, tail or checkmark shaped groynes, L head, straight groynes with pier head (seaward end raised on
250-415: A natural barrier against future disasters like the 2004 Indian Ocean earthquake . Studies have found that an offshore tsunami wall could reduce tsunami wave heights by up to 83%. The appropriate seawall design relies on location-specific aspects, including surrounding erosion processes. There are three main types of seawalls: vertical, curved, stepped, and mounds (see table below). A report published by
300-541: A problem as it is not easy for people to predict or imagine the strength of hurricane or storm-induced waves compared to normal, expected wave patterns. An extreme event can dissipate hundreds of times more energy than everyday waves, and calculating structures that will stand the force of coastal storms is difficult and, often the outcome can become unaffordable. For example, the Omaha Beach seawall in New Zealand
350-402: A rise of between +16-19.3 cm throughout 1900–1988. Superstorm Sandy of 2012 is an example of the devastating effects rising sea levels can cause when mixed with a perfect storm. Superstorm Sandy sent a storm surge of 4–5 m onto New Jersey's and New York's barrier island and urban shorelines, estimated at $ 70 billion in damage. This problem could be overcome by further modeling and determining
400-443: A seawall can be from the area's natural water-table , rain percolating into the ground behind the wall and waves overtopping the wall. The water table can also rise during periods of high water ( high tide ). Lack of adequate drainage can cause the seawall to buckle, move, bow, crack, or collapse. Sinkholes may also develop as the escaping water pressure erodes soil through or around the drainage system. Extreme events also pose
450-539: A series of groynes it occurs after the terminal groyne (last groyne on the downdrift side of the beach or coastline). A breakwater is an artificial offshore structure built parallel to the shore -- similar to naturally formed barrier islands -- that normally remains unattached to the shore. When a groyne is built to attach the breakwater to the shore, it is called a " headland groyne" , also known as "bulkhead groyne", "headland breakwater", "T-head groyne", or "T-shaped groyne". A groyne's length and elevation, and
500-481: A ton, are weathered black and brown. The seawall is inspected every year and whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong. The Union Territory of Pondicherry recorded around 600 deaths from the huge tsunami waves that struck India's coast after the mammoth underwater earthquake (which measured 9.0 on the moment magnitude scale ) off Indonesia, but most of those killed were fishermen who lived in villages beyond
550-399: Is a form of coastal defense constructed where the sea , and associated coastal processes, impact directly upon the landforms of the coast . The purpose of a seawall is to protect areas of human habitation, conservation, and leisure activities from the action of tides , waves , or tsunamis . As a seawall is a static feature, it will conflict with the dynamic nature of the coast and impede
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#1732772584579600-481: Is a static feature which can conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The table below summarizes some positive and negative effects of seawalls which can be used when comparing their effectiveness with other coastal management options, such as beach nourishment . Generally, seawalls can be a successful way to control coastal erosion, but only if they are constructed well and out of materials that can withstand
650-545: Is also a major issue with seawalls. In 2013, more than 5,000 feet (1,500 m) of seawall was found to be crumbling in Punta Gorda, Florida . Residents of the area pay hundreds of dollars each year for a seawall repair program. The problem is that most of the seawalls are over a half-century old and are being destroyed by only heavy downpours. If not kept in check, seawalls lose effectiveness and become expensive to repair. Seawall construction has existed since ancient times. In
700-613: Is believed to be a 100-meter row of boulders in the Mediterranean Sea off the coast of Israel. Boulders were positioned in an attempt to protect the coastal settlement of Tel Hreiz from sea rise following the last glacial maximum . Tel Hreiz was discovered in 1960 by divers searching for shipwrecks, but the row of boulders was not found until storms cleared a sand cover in 2012. More recently, seawalls were constructed in 1623 in Canvey Island , UK, when great floods of
750-670: Is derived from the Old French groign , from Late Latin grunium , " snout ". A large number of groynes were found along a 1,000-kilometre stretch of the river Nile , between the first and the fourth cataract . The earliest ones dated so far were found to be over 3,000 years old, but researchers are hypothising that the technique might already have been understood in the fourth millennium BCE. The newly discovered groynes are located in what are now Egypt ( Aswan ), but mainly in Sudan , in areas of ancient Nubia , some of them built by
800-491: The 2004 Indian Ocean earthquake tsunami crashed against India's south-eastern coastline killing thousands. However, the former French colonial enclave of Pondicherry escaped unscathed. This was primarily due to French engineers who had constructed (and maintained) a massive stone seawall during the time when the city was a French colony. This 300-year-old seawall effectively kept Pondicherry's historic center dry even though tsunami waves drove water 24 ft (7.3 m) above
850-500: The UK , seawall also refers to an earthen bank used to create a polder , or a dike construction . The type of material used for construction is hypothesized to affect the settlement of coastal organisms, although the precise mechanism has yet to be identified. A seawall works by reflecting incident wave energy back into the sea, thus reducing the energy available to cause erosion. Seawalls have two specific weaknesses. Wave reflection from
900-612: The United Nations Environment Programme (UNEP) suggests that the tsunami of 26 December 2004 caused less damage in the areas where natural barriers were present, such as mangroves , coral reefs or coastal vegetation. A Japanese study of this tsunami in Sri Lanka used satellite imagery modelling to establish the parameters of coastal resistance as a function of different types of trees. Natural barriers, such as coral reefs and mangrove forests, prevent
950-510: The Egyptian overlords and some possibly the work of local Nubians. One of the earliest mentions of groynes is in connection with the planned improvements to the silted-up Dover harbour , by one Fernando Poyntz in 1582. In 1713 the first wooden groyne to protect Brighton 's seafront and coastline was built, which had been heavily damaged in the Great storm of 1703 , and again in 1705. In 1867,
1000-506: The Global Positioning System, GPS) indicate a mean rate of sea level rise of 1.6–1.8 mm/yr over the twentieth century. The Intergovernmental Panel on Climate Change (IPCC) (1997) suggested that sea level rise over the next 50 – 100 years will accelerate with a projected increase in global mean sea level of +18 cm by 2050 AD. This data is reinforced by Hannah (1990) who calculated similar statistics including
1050-754: The Living Seawalls project was announced as a finalist for the international environment award the Earthshot Prize . Since 2022 it has become part of Project Restore, under the auspices of the Sydney Institute of Marine Science . Some further issues include a lack of long-term trend data of seawall effects due to a relatively short duration of data records; modeling limitations and comparisons of different projects and their effects being invalid or unequal due to different beach types; materials; currents; and environments. Lack of maintenance
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#17327725845791100-576: The Thames estuary occurred, prompting the construction of protection for further events in this flood-prone area. Since then, seawall design has become more complex and intricate in response to an improvement in materials, technology, and an understanding of how coastal processes operate. This section will outline some key case studies of seawalls in chronological order and describe how they have performed in response to tsunamis or ongoing natural processes and how effective they were in these situations. Analyzing
1150-510: The Vancouver Seawall is a prime example of how seawalls can simultaneously provide shoreline protection and a source of recreation which enhances human enjoyment of the coastal environment. It also illustrates that although shoreline erosion is a natural process, human activities, interactions with the coast, and poorly planned shoreline development projects can accelerate natural erosion rates. On December 26, 2004, towering waves of
1200-427: The artificial barrier which reinforces the effectiveness of seawalls. At least 43 percent of Japan's 29,751 km (18,486 mi) coastline is lined with concrete seawalls or other structures designed to protect the country against high waves, typhoons, or even tsunamis. During the 2011 Tōhoku earthquake and tsunami , the seawalls in most areas were overwhelmed. In Kamaishi , 4-metre (13 ft) waves surmounted
1250-411: The current. Groynes can be submerged or not under normal conditions. Usually impermeable groynes are non-submerged, since flow over the top of solid groynes may cause severe erosion along the shanks. Submerged groynes, on the other hand, may be permeable depending on the degree of flow disturbance needed. Groynes can be attracting, deflecting or repelling. Seawall A seawall (or sea wall )
1300-485: The disruption of sediment movement and transport patterns. Combined with a high construction cost, this has led to increasing use of other soft engineering coastal management options such as beach replenishment . Seawalls are constructed from various materials, most commonly reinforced concrete , boulders, steel, or gabions . Other possible construction materials include vinyl, wood, aluminum, fiberglass composite, and biodegradable sandbags made of jute and coir . In
1350-426: The down-drift side. Groynes are generally placed in series, generally all perpendicular to the shore. The areas between groups of groynes are groyne fields . A poorly designed groyne (too long and not suited to the unique features of the coast) can also accelerate the erosion of the downdrift beach, which receives little or no sand from longshore drift. This process is known as terminal groyne syndrome, because in
1400-454: The earthquake zone, as the tsunami washed over walls that were supposed to protect the plants. Arguably, the additional defense provided by the seawalls presented an extra margin of time for citizens to evacuate and also stopped some of the full force of energy which would have caused the wave to climb higher in the backs of coastal valleys. In contrast, the seawalls also acted in a negative way to trap water and delay its retreat. The failure of
1450-408: The exchange of sediment between land and sea. Seawall designs factor in local climate, coastal position, wave regime (determined by wave characteristics and effectors), and value (morphological characteristics) of landform. Seawalls are hard engineering shore-based structures that protect the coast from erosion. Various environmental issues may arise from the construction of a seawall, including
1500-404: The extension of height and reinforcement of current seawalls which needs to occur for safety to be ensured in both situations. Sea level rise also will cause a higher risk of flooding and taller tsunamis. Seawalls, like all retaining walls , must relieve the buildup of water pressure . Water pressure buildup is caused when groundwater is not drained from behind the seawall. Groundwater against
1550-450: The first century BCE, Romans built a seawall or breakwater at Caesarea Maritima creating an artificial harbor (Sebastos Harbor). The construction used Pozzolana concrete which hardens in contact with seawater. Barges were constructed and filled with the concrete. They were floated into position and sunk. The resulting harbor/breakwater/seawall is still in existence today – more than 2000 years later. The oldest known coastal defense
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1600-410: The first concrete groyne was built near East Street, Brighton as a promenade 195 feet (59 m) long. A groyne gradually creates and maintains a wide area of beach on its updrift side by trapping the sediments suspended in the ocean current. This process is called accretion of sand and gravel or beach evolution . It reduces erosion on the other, i.e. downdrift, side by reducing the speed and power of
1650-402: The force of ongoing wave energy. Some understanding is needed of the coastal processes and morphodynamics specific to the seawall location. Seawalls can be very helpful; they can offer a more long-term solution than soft engineering options, additionally providing recreation opportunities and protection from extreme events as well as everyday erosion. Extreme natural events expose weaknesses in
1700-501: The money dedicated to building new seawalls and protection from future hurricanes. A New York Harbor Storm-Surge Barrier has been proposed, but not voted on or funded by Congress or the State of New York. In Florida, tiger dams are used to protect homes near the coast. General: Related types of walls: Specific walls: River morphology The terms river morphology and its synonym stream morphology are used to describe
1750-454: The normal high-tide mark. The barrier was initially completed in 1735 and over the years, the French continued to fortify the wall, piling huge boulders along its 1.25 mi (2 km) coastline to stop erosion from the waves pounding the harbor. At its highest, the barrier running along the water's edge reaches about 27 ft (8.2 m) above sea level. The boulders, some weighing up to
1800-462: The performance of seawalls, and analyses of these can lead to future improvements and reassessment. Sea level rise creates an issue for seawalls worldwide as it raises both the mean normal water level and the height of waves during extreme weather events, which the current seawall heights may be unable to cope with. The most recent analyses of long, good-quality tide gauge records (corrected for GIA and when possible for other vertical land motions by
1850-403: The rate of plant growth; the availability of sediment ; the size and composition of the sediment moving through the channel; the rate of sediment transport through the channel and the rate of deposition on the floodplain , banks, bars , and bed; and regional aggradation or degradation due to subsidence or uplift . River morphology can also be affected by human interaction, which is a way
1900-559: The river responds to a new factor in how the river can change its course. An example of human induced change in river morphology is dam construction, which alters the ebb flow of fluvial water and sediment, therefore creating or shrinking estuarine channels. A river regime is a dynamic equilibrium system, which is a way of classifying rivers into different categories. The four categories of river regimes are Sinuous canali- form rivers, Sinuous point bar rivers, Sinuous braided rivers, and Non-sinuous braided rivers. The study of river morphology
1950-566: The seafloor. The Living Seawalls project, which was launched in Sydney , Australia, in 2018, aims to help many of the marine species in Sydney Harbour to flourish, thus enhancing its biodiversity , by modifying the design of its seawalls. It entails covering parts of the seawalls with specially-designed tiles that mimic natural microhabitats - with crevices and other features that more closely resemble natural rocks. In September 2021,
2000-481: The seawall began in 1917, and since then this pathway has become one of the most used features of the park by both locals and tourists and now extends 22 km in total. The construction of the seawall also provided employment for relief workers during the Great Depression and seamen from HMCS Discovery on Deadman's Island who were facing punishment detail in the 1950s (Steele, 1985). Overall,
2050-474: The seawall – the world's largest, erected a few years ago in the city's harbor at a depth of 63 m (207 ft), a length of 2 km (1.2 mi) and a cost of $ 1.5 billion – and eventually submerged the city center. The risks of dependence on seawalls were most evident in the crisis at the Fukushima Dai-ichi and Fukushima Dai-ni nuclear power plants , both located along the coast close to
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2100-424: The shapes of river channels and how they change in shape and direction over time. The morphology of a river channel is a function of a number of processes and environmental conditions, including the composition and erodibility of the bed and banks (e.g., sand, clay, bedrock); erosion comes from the power and consistency of the current, and can effect the formation of the river's path. Also, vegetation and
2150-404: The spacing between groynes is determined according to local wave energy and beach slope. Groynes that are too long or too high tend to accelerate downdrift erosion, and are ineffective because they trap too much sediment. Groynes that are too short, too low, or too permeable are ineffective because they trap too little sediment. If a groyne does not extend far enough landward, water (for example at
2200-411: The spread of tsunamis and the flow of coastal waters and mitigated the flood and surge of water. A cost-benefit approach is an effective way to determine whether a seawall is appropriate and whether the benefits are worth the expense. Besides controlling erosion, consideration must be given to the effects of hardening a shoreline on natural coastal ecosystems and human property or activities. A seawall
2250-486: The stilts, since the pier head is raised on the stilts it does not act as the breakwater), T-head ( headland groyne , breakwater attached to the shore with straight groyne, the head/breakwater itself could be shaped straight, Y-shaped, arrow or wing shaped head). Wooden groynes, sheetpile groynes, sandbag groynes, rubble mound or gabion groynes, etc. Groynes can be permeable, allowing the water to flow through at reduced velocities, or impermeable, blocking and deflecting
2300-583: The successes and shortcomings of seawalls during severe natural events allows their weaknesses to be exposed, and areas become visible for future improvement. The Vancouver Seawall is a stone seawall constructed around the perimeter of Stanley Park in Vancouver, British Columbia . The seawall was constructed initially as waves created by ships passing through the First Narrows eroding the area between Prospect Point and Brockton Point. Construction of
2350-549: The wall may result in hydrodynamic scour and subsequent lowering of the sand level of the fronting beach. Seawalls may also accelerate the erosion of adjacent, unprotected coastal areas by affecting the littoral drift process. Different designs of man-made tsunami barriers include building reefs and forests to above-ground and submerged seawalls. Starting just weeks after the disaster, in January 2005, India began planting Casuarina and coconut saplings on its coast as
2400-417: The waves striking the shore. It is a physical barrier to stop sediment transport in the direction of longshore drift (also called longshore transport). If a groyne is correctly designed, then the amount of material it can hold will be limited, and excess sediment will be free to move on through the system. However, if a groyne is too large it may trap too much sediment, which can cause severe beach erosion on
2450-605: The world's largest seawall, which cost $ 1.5 billion to construct, shows that building stronger seawalls to protect larger areas would have been even less cost-effective. In the case of the ongoing crisis at the nuclear power plants, higher and stronger seawalls should have been built if power plants were to be built at that site. Fundamentally, the devastation in coastal areas and a final death toll predicted to exceed 10,000 could push Japan to redesign its seawalls or consider more effective alternative methods of coastal protection for extreme events. Such hardened coastlines can also provide
2500-763: Was designed to prevent erosion from everyday waves only, and when a storm in 1976 carved out ten meters behind the existing seawall, the whole structure was destroyed. The addition of seawalls near marine ecosystems can lead to increased shadowing effects in the waters surrounding the seawall. Shadowing reduces the light and visibility within the water, which may disrupt the distribution as well as foraging capabilities of certain species. The sediment surrounding seawalls tends to have less favorable physical properties (Higher calcification levels, less structural organization of crystalline structure, low silicon content, and less macroscale roughness) when compared to natural shorelines, which can present issues for species that reside on
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