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78-679: The Frisian Islands, along with the mainland coast in the German Bight , form the region of Frisia (German and Dutch: Friesland ), homeland of the Frisian people . Generally, the term Frisian Islands is used for the islands where Frisian is spoken and the population is ethnically Frisian. In contrast, the term Wadden Islands applies to the entire archipelago, including the Dutch -speaking westernmost islands of Texel and Vlieland , Danish -speaking Danish Wadden Sea Islands further north off

156-528: A 16th century shipwreck during a search for containers from MSC Zoe . According to Holland’s National Office for Cultural Heritage, the ship was built circa 1540 in the Netherlands during the reign of Charles V . Researchers also found copper plates with emblem of the Fugger family and wooden beams with a sleek hull about 30 metres long. In Friesland and Groningen plans were made to embank and drain

234-414: A breach may experience flooding similar to a natural event, while damage near a breach can be catastrophic, including carving out deep holes and channels in the nearby landscape. Under natural conditions, floodwaters return quickly to the river channel as water-levels drop. During a levee breach, water pours out into the floodplain and moves down-slope where it is blocked from return to the river. Flooding

312-400: A controlled inundation by the military or a measure to prevent inundation of a larger area surrounded by levees. Levees have also been built as field boundaries and as military defences . More on this type of levee can be found in the article on dry-stone walls . Levees can be permanent earthworks or emergency constructions (often of sandbags ) built hastily in a flood emergency. Some of

390-506: A dam by means of tidal road. The Wadden Islands are in continuous apparent movement. The most important movement is the 'migration': the islands themselves are slowly but certainly moving from West to East. On the West side most of the islands disappear slowly into the sea and on the East side even larger sand-banks arise. This movement is also the reason that most of the villages themselves are on

468-612: A distance of some 610 km (380 mi). The scope and scale of the Mississippi levees has often been compared to the Great Wall of China . The United States Army Corps of Engineers (USACE) recommends and supports cellular confinement technology (geocells) as a best management practice. Particular attention is given to the matter of surface erosion, overtopping prevention and protection of levee crest and downstream slope. Reinforcement with geocells provides tensile force to

546-422: A dyke may be a drainage ditch or a narrow artificial channel off a river or broad for access or mooring, some longer dykes being named, e.g., Candle Dyke. In parts of Britain , particularly Scotland and Northern England , a dyke may be a field wall, generally made with dry stone . The main purpose of artificial levees is to prevent flooding of the adjoining countryside and to slow natural course changes in

624-444: A high suspended sediment fraction and thus are intimately associated with meandering channels, which also are more likely to occur where a river carries large fractions of suspended sediment. For similar reasons, they are also common in tidal creeks, where tides bring in large amounts of coastal silts and muds. High spring tides will cause flooding, and result in the building up of levees. Both natural and man-made levees can fail in

702-662: A line of dunes extending over 500 kilometres (310 mi) from the Netherlands to the mouth of the river Elbe in Germany. The sea broke through the dunes in many places to form the Wadden Islands, with the low-lying country behind becoming the tidal Wadden mudflats . The Dutch West Frisian and the German East Frisian Islands are barrier islands . They arose along the breakers' edge where

780-428: A number of ways. Factors that cause levee failure include overtopping, erosion, structural failures, and levee saturation. The most frequent (and dangerous) is a levee breach . Here, a part of the levee actually breaks or is eroded away, leaving a large opening for water to flood land otherwise protected by the levee. A breach can be a sudden or gradual failure, caused either by surface erosion or by subsurface weakness in

858-471: A particularly well regarded product of local fishing. Energy extraction also plays an important role with Germany's only offshore oil rig ( Mittelplate ) located in the German Bight and an increasing penetration by offshore wind farms such as Alpha Ventus . While offshore wind farms are more expensive to build and require more expensive operations for maintenance and repair than land-based wind turbines

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936-799: A property-boundary marker or drainage channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike , which leads water from the catchwater drain , Car Dyke, to the South Forty Foot Drain in Lincolnshire (TF1427). The Weir Dike is a soak dike in Bourne North Fen , near Twenty and alongside the River Glen , Lincolnshire . In the Norfolk and Suffolk Broads ,

1014-525: A ridge and increasing the river channel's capacity. Alternatively, levees can be artificially constructed from fill , designed to regulate water levels. In some circumstances, artificial levees can be environmentally damaging . Ancient civilizations in the Indus Valley , ancient Egypt, Mesopotamia and China all built levees. Today, levees can be found around the world, and failures of levees due to erosion or other causes can be major disasters, such as

1092-412: A shorter route to the ocean and begin building a new delta. Wave action and ocean currents redistribute some of the sediment to build beaches along the coast. When levees are constructed all the way to the ocean, sediments from flooding events are cut off, the river never migrates, and elevated river velocity delivers sediment to deep water where wave action and ocean currents cannot redistribute. Instead of

1170-421: A shorter time interval means higher river stage (height). As more levees are built upstream, the recurrence interval for high-water events in the river increases, often requiring increases in levee height. During natural flooding, water spilling over banks rises slowly. When a levee fails, a wall of water held back by the levee suddenly pours out over the landscape, much like a dam break. Impacted areas far from

1248-447: A waterway to provide reliable shipping lanes for maritime commerce over time; they also confine the flow of the river, resulting in higher and faster water flow. Levees can be mainly found along the sea, where dunes are not strong enough, along rivers for protection against high floods, along lakes or along polders . Furthermore, levees have been built for the purpose of impoldering, or as a boundary for an inundation area. The latter can be

1326-537: Is electrical resistivity tomography (ERT). This non-destructive geophysical method can detect in advance critical saturation areas in embankments. ERT can thus be used in monitoring of seepage phenomena in earth structures and act as an early warning system, e.g., in critical parts of levees or embankments. Large scale structures designed to modify natural processes inevitably have some drawbacks or negative impacts. Levees interrupt floodplain ecosystems that developed under conditions of seasonal flooding. In many cases,

1404-499: Is a scheduled horse drawn carriage service from the mainland to Neuwerk locally known as a Wattwagen (mud flats wagon). The island of Sylt can be reached by the railway-only Hindenburgdamm causeway which was built after World War I when the port on the mainland from which ferries to Sylt had left up to that point came under Danish rule following the 1920 Schleswig plebiscites . Some of the Halligen also have railway connections to

1482-429: Is an elevated ridge , natural or artificial, alongside the banks of a river , often intended to protect against flooding of the area adjoining the river. It is usually earthen and often runs parallel to the course of a river in its floodplain or along low-lying coastlines. Naturally occuring levees form on river floodplains following flooding, where sediment and alluvium is deposited and settles, forming

1560-546: Is below mean sea level. These typically man-made hydraulic structures are situated to protect against erosion. They are typically placed in alluvial rivers perpendicular, or at an angle, to the bank of the channel or the revetment , and are used widely along coastlines. There are two common types of spur dyke, permeable and impermeable, depending on the materials used to construct them. Natural levees commonly form around lowland rivers and creeks without human intervention. They are elongated ridges of mud and/or silt that form on

1638-420: Is important in order to design stable levee and floodwalls . There have been numerous studies to investigate the erodibility of soils. Briaud et al. (2008) used Erosion Function Apparatus (EFA) test to measure the erodibility of the soils and afterwards by using Chen 3D software, numerical simulations were performed on the levee to find out the velocity vectors in the overtopping water and the generated scour when

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1716-451: Is permanently diverted through the gap. Sometimes levees are said to fail when water overtops the crest of the levee. This will cause flooding on the floodplains, but because it does not damage the levee, it has fewer consequences for future flooding. Among various failure mechanisms that cause levee breaches, soil erosion is found to be one of the most important factors. Predicting soil erosion and scour generation when overtopping happens

1794-573: Is prolonged over such areas, waiting for floodwater to slowly infiltrate and evaporate. Natural flooding adds a layer of sediment to the floodplain. The added weight of such layers over many centuries makes the crust sink deeper into the mantle , much like a floating block of wood is pushed deeper into the water if another board is added on top. The momentum of downward movement does not immediately stop when new sediment layers stop being added, resulting in subsidence (sinking of land surface). In coastal areas, this results in land dipping below sea level,

1872-480: Is thought to date from the 1st or 2nd century BC. In the late Middle Ages , the dike system was gradually strengthened and flooding diminished. Beginning in the 17th century, dikes were built further out to reclaim more land. This activity peaked in the 19th and 20th centuries. The dunes south of the Wadden Sea were also liable to this process, but human intervention prevented the many storm surges from changing

1950-654: The German Bay ) is the southeastern bight of the North Sea bounded by the Netherlands and Germany to the south, and Denmark and Germany to the east (the Jutland peninsula ). To the north and west it is limited by the Dogger Bank . The Bight contains the Frisian and Danish Islands . The Wadden Sea is approximately ten to twelve kilometres wide at the location of the German Bight. The Frisian islands and

2028-525: The Nile Delta on the shores of the Mediterranean . The Mesopotamian civilizations and ancient China also built large levee systems. Because a levee is only as strong as its weakest point, the height and standards of construction have to be consistent along its length. Some authorities have argued that this requires a strong governing authority to guide the work and may have been a catalyst for

2106-571: The Noorderhaaks and Zuiderhaaks . Sometimes such a shoal grows, originating where an island has been 'walking', and the island regains area. (from West to East) The Dutch islands have a surface of 405.2 km² and a total of 23,872 inhabitants. The names of all these places suggest this is the transition area between island and shoal ( plaat in Dutch). Noorderhaaks, Griend, Rottumerplaat and Rottumeroog are generally considered to be islands,

2184-700: The Wadden Sea , a UNESCO World Heritage Site in the "nature" category. Due to being divided among three different states of Germany those protected areas fall into three different national parks, namely the Lower Saxon Wadden Sea National Park , the Schleswig-Holstein Wadden Sea National Park and the small Hamburg Wadden Sea National Park mostly around the island of Neuwerk . Despite or maybe because of its unique natural environment,

2262-564: The 20th century, silt on the islands was a serious problem. To protect them, small woods were planted. Long before the beginning of the modern era, there were already humans inhabiting the Wadden area. Up to 800 AD, most inhabitants lived on terpen (artificial mounds). Living conditions were difficult. The Roman naturalist Pliny , writing in the first century AD, described the Frisians as ... ... people who live without trees or shrubs. ... in

2340-405: The German Bight is also subject to intense economic and recreational use with the Wadden Sea being one of Germany's most popular tourist destinations . Mudflat hiking is a particularly popular tourist activity usually undertaken with licensed guides employed by the national park service. Fishing and mussel banks (particularly oysters ) are other important economic activities with crangon crangon

2418-638: The Mississippi, stretching from Cape Girardeau , Missouri , to the Mississippi delta . They were begun by French settlers in Louisiana in the 18th century to protect the city of New Orleans . The first Louisiana levees were about 90 cm (3 ft) high and covered a distance of about 80 km (50 mi) along the riverside. The U.S. Army Corps of Engineers, in conjunction with the Mississippi River Commission, extended

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2496-878: The North Sea. (from South to North) In the 20th century, south of the Danish island Rømø lay the small island Jordsand , which sank in 1999. North of the Danish island Fanø the sand coast has been opened and closed numerous times in the course of history, but at the moment the coast line is closed, and forms a whole again except for two west coast fjords. The Danish islands have a total surface of 193.8 km² (74.5 sq. mi.) and 4,173 inhabitants. 53°57′N 8°30′E  /  53.950°N 8.500°E  / 53.950; 8.500 German Bight The German Bight ( German : Deutsche Bucht ; Danish : tyske bugt ; Dutch : Duitse bocht ; West Frisian : Dútske bocht ; North Frisian : Schiisk Bocht ; sometimes also

2574-468: The Wadden Sea. As a result, the islands would have become part of the mainland. As of today, nature and environmental movements have been able to prevent this. The only plan ever to be carried out was the construction of a causeway from the Frisian Holwerd to Ameland , in 1872, which was not very successful. Shortly after construction, the causeway had already suffered so much storm damage that

2652-405: The West side of their island. When they were founded they were situated in the center. Over the course of the last few centuries, many houses and even entire villages disappeared into the sea. The second movement is the development of a hook shape. Along the sea breaches hook-shaped sand ridges arise, which change form with the moving of the sea arm. By growth of these hooks new shoals arise such as

2730-674: The approach to the Port of Hamburg passing through it and then the Elbe River estuary. Other important ports along the German Bight are Bremerhaven/Bremen , Emden (important for export of motorcars, particularly those made at the local VW plant) and the JadeWeserPort at Wilhelmshaven which is Germany's only deepwater port . Shipping in the German Bight often relies on tidal channels (called "Priel" in German) for shipping lanes, but as

2808-403: The bush country lies too far away. They braid ropes of sedges and rushes from the marshes with which they make nets to be able to catch fish, and they dig up mud with their hands and dry it more in wind than in the sun, and with soil as fuel they heat their food and their own bodies, frozen in northern wind. Their only drink comes from storing rain water in tanks front of their houses. And these are

2886-657: The catastrophic 2005 levee failures in Greater New Orleans that occurred as a result of Hurricane Katrina . Speakers of American English use the word levee , from the French word levée (from the feminine past participle of the French verb lever , 'to raise'). It originated in New Orleans a few years after the city's founding in 1718 and was later adopted by English speakers. The name derives from

2964-637: The city of Vancouver , British Columbia , there are levees (known locally as dikes, and also referred to as "the sea wall") to protect low-lying land in the Fraser River delta, particularly the city of Richmond on Lulu Island . There are also dikes to protect other locations which have flooded in the past, such as the Pitt Polder, land adjacent to the Pitt River , and other tributary rivers. Coastal flood prevention levees are also common along

3042-443: The coast of the provinces North Holland and South Holland into separate islands with Wadden mudflats behind them. However, around 1200AD, storm surges did break up the northern coast of Western Friesland into five islands. Around 1600AD, four of these along the West coast had been again recovered, but Wieringen , to the south-east of Texel , remained an island up to the 20th century. In 2019, Dutch maritime investigators unearthed

3120-420: The dam was abandoned in 1882. The dam has been almost entirely eroded since then. In the northern Wadden Sea building dams proved to be considerably simpler. Nordstrand is now so much linked to the rampart by dikes that it is difficult to define it as an island, and also Langeness , Oland , Nordstrandischmoor , Hamburger Hallig , Sylt , and Rømø are all reachable by dams. Mandø is even reachable without

3198-488: The development of systems of governance in early civilizations. However, others point to evidence of large-scale water-control earthen works such as canals and/or levees dating from before King Scorpion in Predynastic Egypt , during which governance was far less centralized. Another example of a historical levee that protected the growing city-state of Mēxihco-Tenōchtitlan and the neighboring city of Tlatelōlco,

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3276-588: The earliest levees were constructed by the Indus Valley civilization (in Pakistan and North India from c.  2600 BCE ) on which the agrarian life of the Harappan peoples depended. Levees were also constructed over 3,000 years ago in ancient Egypt , where a system of levees was built along the left bank of the River Nile for more than 1,000 kilometers (600 miles), stretching from modern Aswan to

3354-479: The earth together. On the land side of high levees, a low terrace of earth known as a banquette is usually added as another anti-erosion measure. On the river side, erosion from strong waves or currents presents an even greater threat to the integrity of the levee. The effects of erosion are countered by planting suitable vegetation or installing stones, boulders, weighted matting, or concrete revetments . Separate ditches or drainage tiles are constructed to ensure that

3432-484: The east, to the coasts of the ocean, a number of races in such needy conditions exist; but this also applies to the races of peoples which are called the large and small Chaucen, which we have seen in the north. There, two times in each period of a day and a night, the ocean with a fast tide submerges an immense plain, thereby the hiding ... whether the area is sea or land. There this miserable race inhabits raised pieces ground or platforms, which they have moored by hand above

3510-879: The foundation does not become waterlogged. Prominent levee systems have been built along the Mississippi River and Sacramento River in the United States , and the Po , Rhine , Meuse River , Rhône , Loire , Vistula , the delta formed by the Rhine, Maas/Meuse and Scheldt in the Netherlands and the Danube in Europe . During the Chinese Warring States period , the Dujiangyan irrigation system

3588-403: The government for coastal protection work and to transport goods and personnel. 54°27′14″N 7°12′50″E  /  54.45389°N 7.21389°E  / 54.45389; 7.21389 Levee A levee ( / ˈ l ɛ v i / or / ˈ l ɛ v eɪ / ), dike ( American English ), dyke ( British English ; see spelling differences ), embankment , floodbank , or stop bank

3666-450: The impact is two-fold, as reduced recurrence of flooding also facilitates land-use change from forested floodplain to farms. In a natural watershed, floodwaters spread over a landscape and slowly return to the river. Downstream, the delivery of water from the area of flooding is spread out in time. If levees keep the floodwaters inside a narrow channel, the water is delivered downstream over a shorter time period. The same volume of water over

3744-404: The inland coastline behind the Wadden Sea , an area devastated by many historic floods. Thus the peoples and governments have erected increasingly large and complex flood protection levee systems to stop the sea even during storm floods. The biggest of these are the huge levees in the Netherlands , which have gone beyond just defending against floods, as they have aggressively taken back land that

3822-549: The laboratory tests, empirical correlations related to average overtopping discharge were derived to analyze the resistance of levee against erosion. These equations could only fit to the situation, similar to the experimental tests, while they can give a reasonable estimation if applied to other conditions. Osouli et al. (2014) and Karimpour et al. (2015) conducted lab scale physical modeling of levees to evaluate score characterization of different levees due to floodwall overtopping. Another approach applied to prevent levee failures

3900-455: The last ice age , which ended approximately 12,000 years ago, sea level was about 60 metres (200 ft) lower than it is now, and part of what is now the North Sea was dry land. With the melting of the ice caps, the sea level rose, reaching the current coast line around the beginning of the Holocene era, approximately 7,000 years ago. Tidal action transported large quantities of sand to form

3978-528: The levee system beginning in 1882 to cover the riverbanks from Cairo, Illinois to the mouth of the Mississippi delta in Louisiana. By the mid-1980s, they had reached their present extent and averaged 7.3 m (24 ft) in height; some Mississippi levees are as high as 15 m (50 ft). The Mississippi levees also include some of the longest continuous individual levees in the world. One such levee extends southwards from Pine Bluff , Arkansas , for

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4056-420: The levee. A breach can leave a fan-shaped deposit of sediment radiating away from the breach, described as a crevasse splay . In natural levees, once a breach has occurred, the gap in the levee will remain until it is again filled in by levee building processes. This increases the chances of future breaches occurring in the same location. Breaches can be the location of meander cutoffs if the river flow direction

4134-475: The levees in the area, created for the purpose of farming the fertile tidal marshlands. These levees are referred to as dykes. They are constructed with hinged sluice gates that open on the falling tide to drain freshwater from the agricultural marshlands and close on the rising tide to prevent seawater from entering behind the dyke. These sluice gates are called " aboiteaux ". In the Lower Mainland around

4212-442: The level of the highest known tide. Living in huts built on the chosen spots, they seem like sailors in ships if water covers the surrounding country, but like shipwrecked people when the tide has withdrawn itself, and around their huts they catch fish which try to escape with the expiring tide. It is for them not possible to keep herds and live on milk such as the surrounding tribes. They cannot even fight with wild animals, because all

4290-543: The main channel, this will make levee overtopping more likely again, and the levees can continue to build up. In some cases, this can result in the channel bed eventually rising above the surrounding floodplains, penned in only by the levees around it; an example is the Yellow River in China near the sea, where oceangoing ships appear to sail high above the plain on the elevated river. Levees are common in any river with

4368-620: The mainland but in some cases those are only usable at low tide. Those lines are the Dagebüll–Oland–Langeneß island railway and the Lüttmoorsiel-Nordstrandischmoor island railway . While there is no scheduled traffic, island residents can use their own (usually self-built) rail vehicles. In the past those were sail bogeys , but nowadays most are diesel driven draisines with battery-electric railcars increasingly gaining ground. The rail lines are also used by

4446-410: The mainland. They are, therefore, often higher and their cores are less exposed to changes than the islands to the south. Beyond the core, however, the same processes are at work, as is particularly evident on Sylt , where the south of the island threatens to be broken away and the harbour at List in the north silts up. The Danish Islands, the next in the chain to the north, arose from sandbanks. Into

4524-445: The majority of The Lake being drained in the 17th century. Levees are usually built by piling earth on a cleared, level surface. Broad at the base, they taper to a level top, where temporary embankments or sandbags can be placed. Because flood discharge intensity increases in levees on both river banks , and because silt deposits raise the level of riverbeds , planning and auxiliary measures are vital. Sections are often set back from

4602-537: The nearby coastal areas are collectively known as Frisia . The southern portion of the bight is also known as the Heligoland Bight . Between 1949 and 1956 the BBC Sea Area Forecast (Shipping Forecast) used " Heligoland " as the designation for the area now referred to as German Bight. The German Bight contains some of Germany's largest national parks by area, the aim of which is to protect

4680-399: The ocean migrating inland, and salt-water intruding into freshwater aquifers. Where a large river spills out into the ocean, the velocity of the water suddenly slows and its ability to transport sand and silt decreases. Sediments begin to settle out, eventually forming a delta and extending to the coastline seaward. During subsequent flood events, water spilling out of the channel will find

4758-463: The others are considered to be sandbars and disappear from time to time into the waves. The former island of Wieringen can be found at the top of North Holland , against the Afsluitdijk . (from West to East and South to North) The German islands have a surface of 448.52 km² (173 sq. mi.) and 53,296 inhabitants. It is possible to make a boat excursion from several German Wadden Islands to

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4836-484: The overtopping water impinges the levee. By analyzing the results from EFA test, an erosion chart to categorize erodibility of the soils was developed. Hughes and Nadal in 2009 studied the effect of combination of wave overtopping and storm surge overflow on the erosion and scour generation in levees. The study included hydraulic parameters and flow characteristics such as flow thickness, wave intervals, surge level above levee crown in analyzing scour development. According to

4914-562: The races which, if they were now conquered by the Roman nation, say that they will fall into slavery! It is only too true: Destiny saves people as a punishment. Around 1000AD, dike construction began. Monks were instrumental in this activity, among others those of the monastery of Aduard . But earlier attempts had been undertaken to dam the sea. At the Frisian Peins (near Franeker ), a 40-meter section of dike has been discovered that

4992-454: The rebellious Batavi pierced dikes to flood their land and to protect their retreat (70  CE ). The word dijk originally indicated both the trench and the bank . It closely parallels the English verb to dig . In Anglo-Saxon , the word dic already existed and was pronounced as dick in northern England and as ditch in the south. Similar to Dutch, the English origins of

5070-413: The river floodplains immediately adjacent to the cut banks. Like artificial levees, they act to reduce the likelihood of floodplain inundation. Deposition of levees is a natural consequence of the flooding of meandering rivers which carry high proportions of suspended sediment in the form of fine sands, silts, and muds. Because the carrying capacity of a river depends in part on its depth, the sediment in

5148-440: The river to form a wider channel, and flood valley basins are divided by multiple levees to prevent a single breach from flooding a large area. A levee made from stones laid in horizontal rows with a bed of thin turf between each of them is known as a spetchel . Artificial levees require substantial engineering. Their surface must be protected from erosion, so they are planted with vegetation such as Bermuda grass in order to bind

5226-638: The riverbed, even up to a point where the riverbed is higher than the adjacent ground surface behind the levees, are found for the Yellow River in China and the Mississippi in the United States. Levees are very common on the marshlands bordering the Bay of Fundy in New Brunswick and Nova Scotia , Canada . The Acadians who settled the area can be credited with the original construction of many of

5304-527: The sediment is moved around by tides, wind and waves and as ships reach ever greater draughts extensive dredging is necessary to keep shipping lanes open. Some of the East Frisian Islands can be reached on foot at low tide and the sailing schedules of local ferries are tide-dependent. While the mudflats are usually barred to anything but foot traffic and more heavily protected areas of the national parks are off-limits to all but scientists, there

5382-531: The small rock island of Helgoland which is situated 70 km (43 mi) off the German coast. Although Heligoland (German: Helgoland) is not a Wadden Island, there are strong cultural links with the Wadden area; for example a dialect of North Frisian is spoken there. Not all these islands are officially considered to be Wadden Islands. For the definition of an island, a minimum of 160 hectares (0.6 sq. mi.) must no longer be submerged during average high water by

5460-404: The soil to better resist instability. Artificial levees can lead to an elevation of the natural riverbed over time; whether this happens or not and how fast, depends on different factors, one of them being the amount and type of the bed load of a river. Alluvial rivers with intense accumulations of sediment tend to this behavior. Examples of rivers where artificial levees led to an elevation of

5538-427: The steadier winds out at sea allow for steadier power output and a higher capacity factor . Both these advantages are important enough to justify the higher cost as Germany is in the process of phasing out nuclear energy and plans to phase out all fossil fuels thereafter leaving few dispatchable electricity sources . The German Bight has also played an important role as a shipping lane since medieval times with

5616-441: The trait of the levee's ridges being raised higher than both the channel and the surrounding floodplains. The modern word dike or dyke most likely derives from the Dutch word dijk , with the construction of dikes well attested as early as the 11th century. The 126-kilometer-long (78 mi) Westfriese Omringdijk , completed by 1250, was formed by connecting existing older dikes. The Roman chronicler Tacitus mentions that

5694-524: The water surge piled up sediment, and behind which sediment was carried away by the breaking waves. Over time, shoals arose, which ultimately were only covered by infrequent storm floods. Once plants began to colonize the sandbanks, the land began to stabilize. In contrast, the North Frisian Islands arose from the remains of old Geestland islands, where the land was partially removed by storm floods and water action and then separated from

5772-494: The water which is over the flooded banks of the channel is no longer capable of keeping the same number of fine sediments in suspension as the main thalweg . The extra fine sediments thus settle out quickly on the parts of the floodplain nearest to the channel. Over a significant number of floods, this will eventually result in the building up of ridges in these positions and reducing the likelihood of further floods and episodes of levee building. If aggradation continues to occur in

5850-642: The west coast of Jutland and the Islands of Trischen and Neuwerk . Most of the Wadden Sea Islands are environmentally protected areas, and an international wildlife nature reserve is being coordinated between the Netherlands, Germany and Denmark. Natural gas and oil drilling continue, however, and in the vicinity of the Ems , Weser and Elbe estuaries , and ship traffic causes tension between wildlife protection and economic values. During

5928-482: The word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name may be given to either the excavation or to the bank. Thus Offa's Dyke is a combined structure and Car Dyke is a trench – though it once had raised banks as well. In the English Midlands and East Anglia , and in the United States, a dike is what a ditch is in the south of England,

6006-642: Was built by the Qin as a water conservation and flood control project. The system's infrastructure is located on the Min River , which is the longest tributary of the Yangtze River , in Sichuan , China . The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 5,600 km (3,500 mi) of levees extending some 1,000 km (620 mi) along

6084-488: Was constructed during the early 1400s, under the supervision of the tlahtoani of the altepetl Texcoco, Nezahualcoyotl. Its function was to separate the brackish waters of Lake Texcoco (ideal for the agricultural technique Chināmitls ) from the fresh potable water supplied to the settlements. However, after the Europeans destroyed Tenochtitlan, the levee was also destroyed and flooding became a major problem, which resulted in

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