A polder ( Dutch pronunciation: [ˈpɔldər] ) is a low-lying tract of land that forms an artificial hydrological entity, enclosed by embankments known as dikes . The three types of polder are:
60-573: A koog (plural: köge ) or groden is a type of polder found on the North Sea coast of Germany that is established by the construction of dykes enclosing the land which is then drained to form marshland . This type of land reclamation is also used along rivers. In general, a koog is protected by embankments known as dykes ( Deiche ). Unlike the meaning in modern German, Ingvaeonic *kāg , Old Dutch *kōg , modern Dutch koog and West Frisian Dutch kaag all designate "land outside
120-772: A common feature of beaches and provide a habitat for many organisms. They are useful when preventing the erosion of beaches, and can catch windblown sand which over time increases the natural formation of the beach. To stabilize sand dunes, foredune flora and backdune flora are planted. Foredune flora are typically plants with a tolerance for salt spray, strong winds and are capable surviving being buried underneath blown sand. Some examples are Ammophila arenaria , Honckenya peploides , Cakile maritima , and Spartina coarctata . Whereas backdune flora grow into dense patches called dune mats, which helps to hold dune structure. Examples of backdune flora are Hudsonia tomentosa , spartina patens , and Iva imbricata . After these plants have taken root,
180-486: A managed retreat. The main cost is generally the purchase of land to be abandoned. Relocation compensation may be needed. Human-made structures that will be engulfed by the sea may need to be removed. In some cases, armouring is used to protect land beyond the area to be flooded. Costs may be lowest if existing defences are left to fail naturally, but the realignment project may be more actively managed, for example by creating an artificial breach in existing defences to allow
240-529: A meaning somewhat opposite to that in coastal context. Coastal management Coastal management is defence against flooding and erosion , and techniques that stop erosion to claim lands. Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates due to climate change . Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy. Coastal zones occupy less than 15% of
300-421: A new approach to the design of dikes and other water-retaining structures, based on an acceptable probability of overflowing. Risk is defined as the product of probability and consequences. The potential damage in lives, property, and rebuilding costs is compared with the potential cost of water defences. From these calculations follows an acceptable flood risk from the sea at one in 4,000–10,000 years, while it
360-407: A piece of land elevated above its surroundings, with the augmentative suffix -er and epenthetical -d- . The word has been adopted in thirty-six languages. The Netherlands is frequently associated with polders, as its engineers became noted for developing techniques to drain wetlands and make them usable for agriculture and other development. This is illustrated by the saying "God created
420-463: A quicker fashion. Sand dunes are vulnerable to human activities. Therefore, they need as little human interaction as possible for their protection. Human coastal activities has led to the erosion and loss of plant life on sand dunes. Plant life has been established as an important stabilizing factor of sand dunes and the loss of it will cause more erosion. To prevent this, noticeboards, leaflets, and beach wardens explain to visitors how to avoid damaging
480-538: A river meadow or a carr . Often its name will recall its original situation, for example, the Oderbruch . On the Rhine , Elbe and Oder rivers these areas are also used for flood protection . Once the flooding has subsided, water is pumped out again and the land can be used for farming until the next flood. Until the 1950s, köge were mainly created to reclaim land for farming; since then coastal defence has been
540-577: A river or creek as it discharges across a sandy coastline. The walls stabilise and deepen the channel which benefits navigation, flood management, river erosion and water quality, but can cause coastal erosion by interrupting longshore drift. One solution is a sand bypassing system to pump sand under/around the training walls. Storm surge barriers, or floodgates , were introduced after the North Sea Flood of 1953 and prevent damage from storm surges or any other type of natural disaster that could harm
600-434: A squeeze. An upside to the strategy is that moving seaward (and upward) can create land of high value which can bring investment. Limited intervention is an action taken whereby the management only addresses the problem to a certain extent, usually in areas of low economic significance. Limited intervention often includes the succession of haloseres , including salt marshes and sand dunes. This normally results in protecting
660-400: Is a corresponding loss of beach material on the updrift side, requiring another groyne there. Groynes do not protect the beach against storm-driven waves and if placed too close together create currents that carry material offshore. Shapes of groynes can be straight, outwardly curved away in opposite direction from downdrift. Groynes are cost-effective, require little maintenance and are one of
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#1732780392766720-663: Is a problem along the Hampshire and Sussex coastline in the UK; e.g., at Worthing . Walls of concrete and masonry are used to protect a settlement against erosion or flooding. They are typically about 3–5 metres (10–16 ft) high. Older-style vertical seawalls reflected all the energy of the waves back out to sea, and for this purpose were often given recurved crest walls which increased local turbulence, and thus increased entrainment of sand and sediment. During storms, sea walls help longshore drift. Modern seawalls aim to re-direct most of
780-586: Is an example of measures not related to ports. Protection of the shore in Italy, England and the Netherlands began in the 6th century or earlier. Attack from the sea caused many coastal towns and their harbours to be abandoned. Other harbours were lost due to natural causes such as rapid silting, shoreline advance or retreat, etc. The Venetian Lagoon was one of the few populated coastal areas with continuous prosperity and development where written reports document
840-437: Is generally used to absorb wave energy and hold beach material as riprap does. Often referred to as titan tubes as manufactured by Flint Technical Geosolutions. Longshore drift is not hindered. Boulders and rocks are wired into mesh cages and placed in front of areas vulnerable to erosion: sometimes at cliffs edges or at right angles to the beach. When the ocean lands on the gabion, the water drains through leaving sediment, while
900-401: Is generally used to absorb wave energy and hold beach material. Although effective, this solution is unpopular for aesthetic reasons. Longshore drift is not hindered. Rock armour has a limited lifespan, is not effective in storm conditions and reduces recreational values. Geotextile tubes or geotubes are large geotextile bags placed at the sea edge filled with locally available sand slurry. This
960-608: Is one in 100–2,500 years for a river flood. The particular established policy guides the Dutch government to improve flood defences as new data on threat levels become available. Major Dutch polders and the years they were laid dry include Beemster (1609–1612), Schermer (1633–1635), and Haarlemmermeerpolder (1852). Polders created as part of the Zuiderzee Works include Wieringermeerpolder (1930), Noordoostpolder (1942) and Flevopolder (1956–1968) Several cities on
1020-653: The European Council in 1999. This document was prepared by the Group of Specialists on Coastal Protection and underlies national legislation and practice. The Group of Specialists originated in 1995, pursuant to a decision by the Committee of Ministers of the Council of Europe. It emphasized the need for integrated management and planning, but that coastal areas continued to deteriorate. The Group claimed that this
1080-786: The Paraíba Valley region (in the state of São Paulo ) have polders on land claimed from the floodplains around the Paraíba do Sul river. Bangladesh has 139 polders, of which 49 are sea-facing, while the rest are along the numerous distributaries of the Ganges-Brahmaputra-Meghna River delta. These were constructed in the 1960s to protect the coast from tidal flooding and reduce salinity incursion. They reduce long-term flooding and waterlogging following storm surges from tropical cyclones . They are also cultivated for agriculture. The Jiangnan region, at
1140-486: The Yangtze River Delta , has a long history of constructing polders. Most of these projects were performed between the 10th and 13th centuries. The Chinese government also assisted local communities in constructing dikes for swampland water drainage. The Lijia (里甲) self-monitoring system of 110 households under a lizhang (里长) headman was used for the purposes of service administration and tax collection in
1200-542: The 11th century. The oldest extant polder is the Achtermeer polder, from 1533. As a result of flooding disasters, water boards called waterschap (when situated more inland) or hoogheemraadschap (near the sea, mainly used in the Holland region) were set up to maintain the integrity of the water defences around polders, maintain the waterways inside a polder, and control the various water levels inside and outside
1260-429: The 20th century) or in older times, were formed as a result of dyke enclosure and Aufspülung , as is often the case with polders. Because a koog often lies below the level of the adjacent sea or river, it has to be continually drained. This is carried out with the aid of soakaways , sluices , pumping stations and water pumps . Today the pumps are powered by engines, in pre-industrial times and sometimes even into
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#17327803927661320-699: The Earth's land area, while they host more than 40% of the world population. Nearly 1.2 billion people live within 100 kilometres (62 mi) of a coastline and 100 metres (328 ft) of sea level , with an average density three times higher than the global average for population. With three-quarters of the world population expected to reside in the coastal zone by 2025, human activities originating from this small land area will impose heavy pressure on coasts. Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities. Coastal engineering of harbours began with
1380-638: The adjacent regions of East Frisia the word polder (Low German: Poller ) is used for land enclosed by embankments from where the water is artificially drained. The etymology of the word polder/poller is unclear but it is probably related to English pool . The term groden (c.f. the English verb "to grow") used in Lower Saxony , particularly in the eastern part of East Frisia and in the Oldenburg Land , refers to new areas of land washed up by
1440-428: The air. Polders are at risk of flooding at all times, and care must be taken to protect the surrounding dikes. Dikes are typically built with locally available materials, and each material has its own risks: sand is prone to collapse owing to saturation by water; dry peat is lighter than water and potentially unable to retain water in very dry seasons. Some animals dig tunnels in the barrier, allowing water to infiltrate
1500-587: The area they protect. They are habitually open and allow free passage, but close under threat of a storm surge. The Thames Barrier is an example of such a structure. Beach replenishment/nourishment involves importing sand from elsewhere and adding it to the existing beach. The imported sand should be of a similar quality to the existing beach material so it can meld with the natural local processes and without adverse effects. Beach nourishment can be used in combination with groynes. The scheme requires repeated applications on an annual or multi-year cycle. Sand dunes are
1560-409: The back-shore. These techniques include beach nourishment and sand dune stabilization . Historically coastal strategies were heavily based on static structures, while coastal areas otherwise reflect a dynamic equilibrium . Armouring often has the unintended consequence of moving the problem to another part of the coast. Soft options such as beach nourishment protect coastlines and help to restore
1620-456: The coast, usually towards the back of the beach to protect the area beyond. The most basic revetments consist of timber slants with a possible rock infill. Waves break against the revetments, which dissipate and absorb the energy. The shoreline is protected by the beach material held behind the barriers, as the revetments trap some of the material. They may be watertight, covering the slope completely, or porous, to allow water to filter through after
1680-450: The coastline to trap the sedimentation of longshore drift to gradually create a beach and for it ongoing protection by eliminating coastal erosion, often made of greenharts, concrete, rock or wood. Material builds up on the downdrift side, where littoral drift is predominantly in one direction, creating a wider and a more plentiful beach, thereby protecting the coast because the sand material filters and absorbs wave energy. However, there
1740-537: The dike". In the Netherlands, it primarily survives in place names (e.g. De Koog , Koog aan de Zaan , Kaag ). From the Dithmarschen word koch (15th and 16th centuries), it went into Danish as kog . In North Frisian it is kuch . The spelling koog was used by the poet Michael Richey in 1755 and around 1700, what is now the port of Cuxhaven was still called Koogshaven . In the Netherlands and in
1800-641: The evolution of coastal protection works. In other words, this is one of the first accounts of the use of a sea wall to protect a coastal settlement. Little improvement took place beyond the Roman approach to harbour construction after the Renaissance . Then in the early 19th century, the advent of the steam engine , the search for new lands and trade routes, the expansion of the British Empire through her colonies, and other influences, all contributed to
1860-541: The first dredgers in the Netherlands to maintain the harbour at Velsen . Silting problems there were solved when the previously sealed solid piers were replaced with new "open"-piled jetties . Ancient harbour works are still visible, but most of them disappeared following the fall of the Western Roman Empire even if submerged remains are sometimes still visible under water. Although most coastal efforts were directed to port structures, Venice and its lagoon
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1920-508: The incident energy in the form of sloping revetments, resulting in low reflected waves and much reduced turbulence. Designs use porous designs of rock, concrete armour ( Tetrapods , Seabees , SHEDs, Xblocs , etc.) with flights of steps for beach access. The location of a seawall, must consider the swept prism of the beach profile, the consequences of long-term beach recession and amenity crest level, including cost implications. Sea walls can cause beaches to dissipate. Their presence also alters
1980-546: The land adjacent to the sea is low in value. A decision is made to allow the land to erode and flood, creating new shoreline habitats. This process may continue over many years. The earliest managed retreat in the UK was an area of 0.8 ha at Northey Island flooded in 1991. This was followed by Tollesbury and Orplands in Essex , where the sea walls were breached in 1995. In the Ebro Delta (Spain) coastal authorities planned
2040-428: The land behind the halosere, as wave energy dissipates throughout the accumulated sediment and additional vegetation in the new habitat. Although the halosere is not strictly man-made, as many natural processes contribute to the succession, anthropogenic factors are partially responsible for the formation, since an initial factor was needed to help start the process of succession. Groynes are ert or walls perpendicular to
2100-580: The landscape that they are trying to protect. Modern examples can be found at Cronulla (NSW, 1985–6), Blackpool (1986–2001), Lincolnshire (1992–1997) and Wallasey (1983–1993). At Sandwich, Kent the Seabee seawall is buried at the back of the beach under the shingle with crest level at road kerb level. Sea walls typically cost £10,000 per metre (depending on material, height and width), £10,000,000 per km (depending on material, height and width). Revetments are slanted or upright blockades, built parallel to
2160-587: The main aim. On the western coast of Schleswig-Holstein and on the shores of the Lower Elbe over 230 koogs have been created over the centuries. The oldest ones are in the borough of Eiderstedt ; they date to the 11th century. After the Burchardi flood of 1634, an increasing number of " octroi " koogs were built. Well known koogs include: Polder The ground level in drained marshes subsides over time. All polders will eventually be below
2220-420: The most common defences. However, groynes are increasingly viewed as detrimental to the aesthetics of the coastline and face opposition in many coastal communities. Groynes can be considered a "soft" solution because of the beach enhancement. Groyne construction creates a problem known as terminal groyne syndrome. The terminal groyne prevents longshore drift from bringing material to other nearby places. This
2280-482: The natural dynamism, although they require repeated applications. Maintenance costs can eventually require a strategy change. In some cases a seaward strategy can be adopted. Examples from erosion include: Koge Bay (Dk), Western Scheldt estuary (Nl), Chatelaillon (Fr) and Ebro delta (Sp). There is an obvious downside to this strategy. Coastal erosion is already widespread, and there are many coasts where exceptional high tides or storm surges result in encroachment on
2340-409: The need to address the changes. Growth management can be a challenge for local authorities who must provide the infrastructure required by new residents. Managed retreat is an alternative to constructing or maintaining coastal structures. Managed retreat allows an area to erode. Managed retreat is often a response to a change in sediment budget or to sea level rise . The technique is used when
2400-552: The newly dyked areas of marsh. In this way a so-called "polder staircase" is formed. The name groden is found for example in the borough of Wilhelmshaven in the villages of Altengroden, Neuengroden and Fedderwardergroden , the Heppenser , Voslapper and Rüstersieler Groden, and in the surrounding area are the Cäciliengroden , Petersgroden and Adelheidsgroden. All these areas, whether they emerged more recently (i.e. in
2460-566: The origin of maritime traffic, perhaps before 3500 B.C. Docks , breakwaters and other harbour works were built by hand, often in a grand scale. The Romans introduced many innovations in harbour design. They built walls underwater and constructed solid breakwaters . These structures were made using Roman concrete . Vitruvius described three methods for building port structures ( De Architectura , 5, 12). Other types of port structure such as rubble mounds and arched breakwaters built by means of timber floating caissons were used also. Romans were
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2520-419: The period of intense industrialisation, they were driven by wind power ( wind pumps ). The groups of wind mills on the dykes of the Rhine delta - a symbol of the Netherlands - are old water pumps. As well land reclaimed from the sea, a koog may also refer to land reclaimed alongside rivers. These are usually wet areas that are now used for agriculture. This entails creating a completely new ecosystem from
2580-551: The polder, with a liangzhang (粮长, grain chief) responsible for maintaining the water system and a tangzhang (塘长, dike chief) for polder maintenance. In Germany, land reclaimed by diking is called a koog . The German Deichgraf system was similar to the Dutch and is widely known from Theodor Storm 's novella The Rider on the White Horse . In southern Germany, the term polder is used for retention basins recreated by opening dikes during river floodplain restoration ,
2640-485: The polder. Water boards hold separate elections, levy taxes, and function independently from other government bodies. Their function is basically unchanged even today. As such, they are the oldest democratic institutions in the country. The necessary cooperation among all ranks to maintain polder integrity gave its name to the Dutch version of third-way politics —the Polder Model . The 1953 flood disaster prompted
2700-799: The polders into an inaccessible swamp, which allowed the Allied armies to stop the German army . The Netherlands has a large area of polders: as much as 20% of the land area has at some point in the past been reclaimed from the sea, thus contributing to the development of the country. IJsselmeer is the most famous polder project of the Netherlands. Some other countries which have polders are Bangladesh , Belgium , Canada and China . Some examples of Dutch polder projects are Beemster , Schermer , Flevopolder and Noordoostpolder . The Dutch word polder derives successively from Middle Dutch polre , from Old Dutch polra , and ultimately from pol- ,
2760-426: The protection impeded recreational uses. Erosion continued, but the structures remained, resulting in a loss of beach area. The obtrusiveness and cost of these structures led in the late 1940s and early 1950s, to a more dynamic approach. Projects attempted to replicate the protective characteristics of natural beach and dune systems. The resultant use of artificial beaches and stabilized dunes as an engineering approach
2820-501: The revitalization of sea trade and a renewed interest in port works. Prior to the 1950s, the general practice was to use hard structures to protect against beach erosion or storm damages. These structures included seawalls and revetments or sand-trapping structures such as groynes. During the 1920s and '30s, private or local community interests protected many coastal areas using these techniques on an ad hoc basis. In certain resort areas, structures proliferated to such an extent that
2880-764: The sea in at a particular place in a controlled fashion, or by pre-forming drainage channels for created salt-marsh. Managed retreat has become more of a necessary strategy due to climate change, as adaptation strategies can only do so much to stop sea level rise. Holding the line typically involves shoreline hardening techniques, e.g., using permanent concrete and rock constructions. These techniques-- seawalls , groynes , detached breakwaters , and revetments —represent more than 70% of protected shorelines in Europe. Alternatively, soft engineering techniques supporting natural processes and relying on natural elements such as dunes and vegetation can prevent erosive forces from reaching
2940-452: The sea. Sediments are deposited by the sea on mud flats when the tides change. After reaching a certain height, the land is dyked. Dyked land becomes innengroden . As a result of draining the fertile soil compacts and, over time, can sink until it is below sea level. The rising sea level in front of the dyke and the sinking of the old, now drained, sea areas behind the dyke leads to further dykes being built at an ever-higher level to enclose
3000-472: The shore, impinging on human activity. If the sea rises, many coasts that are developed with infrastructure along or close to the shoreline will be unable to accommodate erosion. They will experience a so-called "coastal squeeze" whereby ecological or geomorphological zones that would normally retreat landwards encounter solid structures and can migrate no further. Wetlands, salt marshes, mangroves and adjacent fresh water wetlands are particularly vulnerable to such
3060-482: The shrub stage begins. Since the previously established plants have stabilized the dunes, during the shrub stage larger plants with bigger root systems are able to grow. This allows for further stabilization of sand dunes. These larger plants, along with wooden sand fences , footpaths, Dutch ladders and boardwalks help to catch windblown sand. Stabilizing sand dunes with plants is a common practice and can be implemented on private and public beaches. When implementing
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#17327803927663120-426: The stabilization sand dunes on privately owned beaches with multiple owners, coming to a consensual agreement tends to be complicated. Some owners may prefer to leave the dunes bare, while others would rather plant more visually appealing plants. In comparison, when implementing dune stabilization on publicly owned beaches, there are less parties to confer with. Therefore, agreements about implementation can be reached in
3180-436: The structure absorbs a moderate amount of wave energy. Gabions need to be securely tied to protect the structure. Downsides include wear rates and visual intrusiveness. Concrete blocks and/or boulders are sunk offshore to alter wave direction and to filter wave and tide energy. The waves break further offshore and therefore lose erosive power. This leads to wider beaches, which further absorb wave energy. Dolos has replaced
3240-569: The structure; the muskrat is known for this activity and hunted in certain European countries because of it. Polders are most commonly, though not exclusively, found in river deltas, former fenlands , and coastal areas. Flooding of polders has also been used as a military tactic in the past. One example is the flooding of the polders along the Yser River during World War I . Opening the sluices at high tide and closing them at low tide turned
3300-543: The surrounding water level some or all of the time. Water enters the low-lying polder through infiltration and water pressure of groundwater , or rainfall, or transport of water by rivers and canals. This usually means that the polder has an excess of water, which is pumped out or drained by opening sluices at low tide . Care must be taken not to set the internal water level too low. Polder land made up of peat (former marshland) will sink in relation to its previous level, because of peat decomposing when exposed to oxygen from
3360-411: The use of concrete blocks because it is more resistant to wave action and requires less concrete to produce a superior result. Similar concrete objects like Dolos are A-jack , Akmon , Xbloc , Tetrapod and Accropode . Cliff stabilization can be accomplished through drainage of excess rainwater of through terracing, planting and wiring to hold cliffs in place. Training walls are built to constrain
3420-405: The wave energy has been dissipated. Most revetments do not significantly interfere with transport of longshore drift. Since the wall absorbs energy instead of reflecting, the surf progressively erodes and destroys the revetment; therefore, maintenance is ongoing, as determined by the structural material and product quality. Rock armour is large rocks placed at the sea edge using local material. This
3480-489: The world, but the Dutch created the Netherlands". The Dutch have a long history of reclamation of marshes and fenland, resulting in some 3,000 polders nationwide. By 1961, about half of the country's land, 18,000 square kilometres (6,800 sq mi), was reclaimed from the sea. About half the total surface area of polders in northwest Europe is in the Netherlands. The first embankments in Europe were constructed in Roman times. The first polders were constructed in
3540-742: Was due to difficulties in implementing the concept of "integrated management". The Group proposed that the Council of Europe , cooperate with the Coastal & Marine Union (EUCC) and United Nations Environment Programme (UNEP). Five generic strategies are involved in coastal defense: The choice of strategy is site-specific, depending on pattern of sea-level change, geomorphological setting, sediment availability and erosion, as well as social, economic and political factors. Alternatively, integrated coastal zone management approaches may be used to prevent development in erosion- or flood-prone areas, reducing
3600-519: Was economically viable and more environmentally friendly. Limited knowledge of coastal sediment transport processes often resulted in inappropriate measures of coastal erosion mitigation. In many cases, measures worked locally, but exacerbated problems at other locations -up to tens of kilometers away- or generated other environmental problems. The essential source on coastal engineering is the European Code of Conduct for Coastal Zones issued by
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