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78-517: The city was first mentioned in 1213 as Wilsem, and means "settlement of Willa (person)". Wilsum developed on the dike along the IJssel River. Wilsum received city rights in 1331. The Dutch Reformed church was built in the middle of the 11 century. The spire dates from 1837. The tower probably served as a place of refuge as well, because the top can only be reached by a ladder. Thanks to several restorations (the last one being between 1980 and 1983)

156-640: A scheduled monument . However, some parts of the Dyke may also remain buried under later development. Some sections are also defined as Sites of Special Scientific Interest , including stretches within the Lower Wye Valley SSSI and the Highbury Wood National Nature Reserve . Parts are located within the Wye Valley and Shropshire Hills Areas of Outstanding Natural Beauty . Most of

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

390-600: 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

468-422: 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

546-648: A great trench and strong rampart, fortified with several towers, from sea to sea. Bede’s Ecclesiastical History of England, Bk 1-5 However, the solution to the problem lies a few chapters later in Bede's account. In Book One Chapter Twelve of Bede's Ecclesiastical History , he writes that the Romans "built a strong wall of stone directly from sea to sea in a straight line between the towns that had been built as strong-points, where Severus had built his earthwork ... straight from east to west". The strong wall of stone cannot refer to

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

702-401: A natural wedge shaped delta forming, a " birds-foot delta " extends far out into the ocean. The results for surrounding land include beach depletion, subsidence, salt-water intrusion, and land loss. Offa%27s Dyke Offa's Dyke ( Welsh : Clawdd Offa ) is a large linear earthwork that roughly follows the border between England and Wales . The structure is named after Offa ,

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

858-754: 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 ,

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936-519: 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

1014-455: A series of dates. In one section, these ranged from AD 430 to AD 652 and in another section from AD 887 to AD 1019: confirming that the bank is clearly post-Roman, and that at least some rebuilding work took place after Offa's reign. It has been suggested that Offa's Dyke may have been a long-term project by several Mercian kings. Further excavations by Clwyd-Powys Archaeological Trust on the Dyke at Chirk Castle found well-preserved remains of

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,

1404-429: 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

1482-546: 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

1560-420: 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

1638-413: Is now often seen as secondary to the modern path, and heritage advice about individual dyke sections is not generally coordinated via any connected overview of the values of the whole monument. Moreover, despite the lasting legacy of Offa's Dyke for English and Welsh communities alike, there is limited public awareness of the monument and its remarkable link to modern ideas of national identity. The proposal

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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,

1872-593: Is protected as a scheduled monument . Some of its route is followed by the Offa's Dyke Path , a 177-mile (285 km) long-distance footpath that runs between Liverpool Bay in the north and the Severn Estuary in the south. Although the Dyke has conventionally been dated to the Early Middle Ages of Anglo-Saxon England, research in recent decades – using techniques such as radioactive carbon dating – has challenged

1950-525: The Anglo-Saxon king of Mercia from AD 757 until 796, who is traditionally believed to have ordered its construction. Although its precise original purpose is debated, it delineated the border between Anglian Mercia and the Welsh kingdom of Powys . The earthwork, which was up to 65 feet (20 m) wide (including its flanking ditch) and 8 feet (2.4 m) high, traversed low ground, hills and rivers. Today it

2028-512: 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

2106-584: The Wall of Severus , a structure built by Septimius Severus , who was Roman Emperor between 193 and 211: Novissimum bellum in Britannia habuit, utque receptas provincias omni securitate muniret, vallum per CXXXIII passuum milia a mari ad mare deduxit. Decessit Eboraci admodum senex, imperii anno sexto decimo, mense tertio. Historiae Romanae Breviarium, viii 19.1 He had his most recent war in Britain, and to fortify

2184-527: The Antonine Wall or Offa's Dyke, so it clearly refers to Hadrian's Wall, especially as Offa's Dyke runs from north to south. Also, as Severus's earthwork is described as being in the same location as Hadrian's Wall, it cannot be Offa's Dyke either, so the earth rampart with a great trench that Bede refers to must be the Vallum , the adjoining earthen barrier immediately south of Hadrian's Wall. Where Bede got it wrong

2262-629: The Dark Ages (aired in 1979), show support for Noble's idea. Most recently, Hill and Margaret Worthington have undertaken considerable research on the Dyke. Their work, though far from finished, has demonstrated that there is little evidence for the Dyke stretching from sea to sea. Rather, they claim that it is a shorter structure stretching from Rushock Hill north of the Herefordshire Plain to Llanfynydd , near Mold, Flintshire , some 64 miles (103 km). According to Hill and Worthington, dykes in

2340-509: The Dyke itself, the Path is longer, and in some places passes at some distance from the earthworks. Opened on 10 July 1971, the Path is one of Britain's longest National Trails , stretching for 283 km (176 mi) from the Severn estuary at Sedbury , near Chepstow , to Prestatyn on the north Wales coast. There is a visitor centre at Knighton . The dyke has a cultural significance symbolising

2418-470: The Dyke seriously compared their conclusions with the late 9th-century writer Asser , who wrote: "there was in Mercia in fairly recent time a certain vigorous king called Offa, who terrified all the neighbouring kings and provinces around him, and who had a great dyke built between Wales and Mercia from sea to sea". In 1955, Sir Cyril Fox published the first major survey of the Dyke. He concurred with Asser that

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2496-608: The Dyke was proposed by the Offa's Dyke Association and local authorities for World Heritage Site status. Part of the proposal stated: Offa’s Dyke is a victim of its very scale, nature, meaning and historical success. It is located in two countries, six local authority areas, multiple ownerships and multiple land-use contexts. The main professional stakeholders – such as the English and Welsh path and heritage management agencies – are organisationally and functionally separate. The ancient monument

2574-659: The Fortress of Penygadden." And, for Gwent, Offa had the dyke built "on the eastern crest of the gorge, clearly with the intention of recognizing that the River Wye and its traffic belonged to the kingdom of Gwent". Ongoing research and archaeology on Offa's Dyke has been undertaken for many years by the Extra-Mural Department of the University of Manchester . Interviews with Dr David Hill, broadcast in episode 1 of In Search of

2652-615: 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

2730-614: The Welsh (western) side, with the displaced soil piled into a bank on the Mercian (eastern) side. This suggests that Mercians constructed it as a defensive earthwork, or to demonstrate the power and intent of their kingdom. Throughout its entire length, the Dyke provides an uninterrupted view from Mercia into Wales. Where the earthwork encounters hills or high ground, it passes to the west of them. Although historians often overlook Offa's reign because of limitations in source material, he ranks as one of

2808-425: The accepted historiography of Offa's Dyke. Noble postulated that the gaps in the Dyke were not due to the incorporation of natural features as defensive barriers, but instead the gaps were a "ridden boundary", perhaps incorporating palisades , that left no archaeological trace. Noble also helped establish the Offa's Dyke Association, which maintains the Offa's Dyke Path . This long-distance footpath mostly follows

2886-544: The burnt charcoal and burnt clay in situ showed it was covered by earth on or around AD 446. Archaeologists concluded that this part of Wat's Dyke, so long thought of as Anglo-Saxon and a mid-8th-century contemporary of Offa's Dyke, must have been built 300 years earlier in the post-Roman period . In 2014, excavations by the Clwyd-Powys Archaeological Trust focused on nine samples of the Dyke near Chirk . Radiocarbon dating of redeposited turf resulted in

2964-634: 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

3042-581: The church is still in a very good state. In 1527, a sconce was built near the city, however it was destroyed the next year. Wilsum was home to 435 people in 1840. Wilsum was a separate municipality until 1937, when it became a part of IJsselmuiden . This Overijssel location article is a stub . You can help Misplaced Pages by expanding it . Dyke (embankment) 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

3120-619: 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

3198-536: The conquered provinces with all security, he built a wall for 133 miles from sea to sea. He died at York, a reasonably old man, in the sixteenth year and third month of his reign. This source is conventionally thought to be referring, in error, to either Hadrian's Wall , 73 miles (117 km), or the Antonine Wall , 37 miles (60 km), which were both shorter and built in the 2nd century. Recently, some writers have suggested that Eutropius may have been referring to

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3276-509: The conventional historiography and theories about the earthwork and shows that part was started in the early 5th century, during the sub-Roman period . The generally accepted theory of the earthwork attributes most of its construction to Offa , King of Mercia from 757 to 796. The structure did not represent a mutually agreed boundary between the Mercians and the Kingdom of Powys . It had a ditch on

3354-480: 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,

3432-623: The ditch under later parkland; radiocarbon samples were recovered, but the results have not yet been made public. The England–Wales border still mostly passes within a few miles of the course of Offa's Dyke through the Welsh Marches . A 3-mile (4.8 km) section of the Dyke which overlooks Tintern Abbey and includes the Devil's Pulpit near Chepstow is now managed by English Heritage . All sections of Offa's Dyke that survive as visible earthworks, or as infilled but undeveloped ditch, are designated as

3510-572: 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

3588-479: 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

3666-424: The earthwork later called Offa's Dyke. Most archaeologists reject this theory. The Venerable Bede also mentions the barrier built by Septimus Severus, but Bede says that the rampart was made of earth and timber, a description which would closer match Offa's Dyke than Hadrian's Wall , though it would describe the Antonine Wall : After many great and severe battles, (Severus) thought fit to divide that part of

3744-642: The earthwork ran 'from sea to sea', theorising that the Dyke ran from the River Dee estuary in the north to the River Wye in the south: approximately 150 miles (240 km). Although Fox observed that Offa's Dyke was not a continuous linear structure, he concluded that earthworks were raised in only those areas where natural barriers did not already exist. Sir Frank Stenton , the UK's most eminent 20th-century scholar on Anglo-Saxon England , accepted Fox's conclusions. He wrote

3822-513: The far north and south may have different dates, and though they may be connected with Offa's Dyke, there is as yet no compelling evidence behind this. However, not all experts accept this view. 'Ofer' means 'border' or 'edge' in Old English, giving rise to the possibility of alternative derivations for some border features associated with Offa. The Roman historian Eutropius in his book Historiae Romanae Breviarium , written around 369, mentions

3900-886: 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

3978-577: The greatest Anglo-Saxon rulers – as evidenced in his ability to raise the workforce and resources required to construct Offa's Dyke. The construction of the earthwork probably involved a corvée system requiring vassals to build certain lengths of the earthwork for Offa in addition to performing their normal services to their king. The Tribal Hidage , a primary document, shows the distribution of land within 8th-century Britain; it shows that peoples were located within specified territories for administration. The first historians and archaeologists to examine

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4056-450: 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

4134-456: 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

4212-490: The introduction to Fox's account of the Dyke. Although Fox's work has now been revised to some extent, it still remains a vital record of some stretches of Offa's Dyke that still existed between 1926 and 1928, when his three field surveys took place, but have since been destroyed. In 1978, Dr Frank Noble challenged some of Fox's conclusions, stirring up new academic interest in Offa's Dyke. His MPhil thesis entitled "Offa's Dyke Reviewed" (1978) raised several questions concerning

4290-443: The island, which he had recovered, from the other unconquered nations, not with a wall, as some imagine, but with a rampart. For a wall is made of stones, but a rampart, with which camps are fortified to repel the assaults of enemies, is made of sods, cut out of the earth, and raised high above the ground, like a wall, having in front of it the trench whence the sods were taken, with strong stakes of wood fixed above it. Thus Severus drew

4368-549: 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

4446-523: 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

4524-420: 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

4602-468: 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

4680-419: The line of Offa's Dyke is designated as a public right of way , including those sections which form part of the Offa's Dyke Path. In August 2013, a 45-metre (148 ft) section of Dyke, between Chirk and Llangollen , was destroyed by a local landowner. The destruction of the Dyke to build a stable was said to be like "driving a road through Stonehenge ", but the perpetrator escaped punishment. In 2010,

4758-533: 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

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4836-445: 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

4914-399: 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

4992-484: 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

5070-399: 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

5148-413: 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

5226-440: 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

5304-617: 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

5382-466: The route of the dyke and is a designated British National Trail . John Davies wrote of Fox's study: "In the planning of it, there was a degree of consultation with the kings of Powys and Gwent. On the Long Mountain near Trelystan , the dyke veers to the east, leaving the fertile slopes in the hands of the Welsh; near Rhiwabon , it was designed to ensure that Cadell ap Brochwel retained possession of

5460-457: The separation between England and Wales: a symbolism similar to Hadrian's Wall between England and Scotland in the Scottish Marches . George Borrow , in his Wild Wales (1862), drawn from folklore , claimed that: [It] was customary for the English to cut off the ears of every Welshman who was found to the east of the dyke, and for the Welsh to hang every Englishman whom they found to

5538-404: 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

5616-488: 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

5694-494: 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

5772-474: 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,

5850-622: 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

5928-483: 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

6006-567: Was in attributing the Vallum to Septimius Severus, and saying that it predated the Wall. In fact the Vallum was the work of Hadrian , and slightly post-dated the Wall. Evidence has also been found that challenges the accepted date of the construction of Offa's Dyke. In December 1999, Shropshire County Council archaeologists uncovered the remains of a hearth or fire on the original ground surface beneath Wat's Dyke near Oswestry . Carbon dating analysis of

6084-505: Was rejected in 2011. The Offa's Dyke Centre is a purpose-built information centre in the town of Knighton , on Offa's Dyke on the border between England ( Shropshire ) and Wales ( Powys ). Some of the best remains of the earthworks can be seen within a two-minute walk from the centre. The Offa's Dyke Path (Welsh: Llwybr Clawdd Offa ) is a long-distance footpath close to the England–Wales border . Although large sections are close to

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