Friesland historically known as Frisia, is a province of the Netherlands located in the northern part of the country. It is situated west of Groningen, northwest of Drenthe and Overijssel, north of Flevoland, northeast of North Holland, south of the Wadden Sea. In 2015, the province had a population of 646,092 and a total area of 5,100 km2; the capital and seat of the provincial government is the city of Leeuwarden, a city with 91,817 inhabitants. Since 2017, Arno Brok is the King's Commissioner in the province. A coalition of the Labour Party, the Christian Democratic Appeal, the Frisian National Party forms the executive branch; the province is divided into 18 municipalities. The area of the province was once part of the ancient, larger region of Frisia; the official languages of Friesland are West Dutch. In 1996 the States of Friesland resolved that the official name of the province should follow the West Frisian spelling rather than the Dutch spelling, resulting in "Friesland" being replaced by "Fryslân".
In 2004 the Dutch government confirmed this resolution, putting in place a three-year scheme to oversee the name change and associated cultural programme. The province of Friesland is referred to as "Frisia" by, amongst others, Hanno Brand, head of the history and literature department at the Fryske Akademy since 2009. However, the English-language webpage of the Friesland Provincial Council refers to the province as "Fryslân"; the Frisii were among the migrating Germanic tribes that, following the breakup of Celtic Europe in the 4th century BC, settled along the North Sea. They came to control the area from present-day Bremen to Brugge, conquered many of the smaller offshore islands. What little is known of the Frisii is provided by a few Roman accounts, most of them military. Pliny the Elder said their lands were forest-covered with tall trees growing up to the edge of the lakes, they lived by raising cattle. In his Germania, Tacitus would describe all the Germanic peoples of the region as having elected kings with limited powers and influential military leaders who led by example rather than by authority.
The people lived in spread-out settlements. He noted the weakness of Germanic political hierarchies in reference to the Frisii, when he mentioned the names of two kings of the 1st century Frisii and added that they were kings "as far as the Germans are under kings". In the 1st century BC, the Frisii halted a Roman advance and thus managed to maintain their independence; some or all of the Frisii may have joined into the Frankish and Saxon peoples in late Roman times, but they would retain a separate identity in Roman eyes until at least 296, when they were forcibly resettled as laeti and thereafter disappear from recorded history. Their tentative existence in the 4th century is confirmed by archaeological discovery of a type of earthenware unique to 4th-century Frisia, called terp Tritzum, showing that an unknown number of Frisii were resettled in Flanders and Kent as laeti under the aforementioned Roman coercion; the lands of the Frisii were abandoned by c. 400 as a result of the conflicts of the Migration Period, climate deterioration, the flooding caused by a rise in the sea level.
The area lay empty for one or two centuries, when changing environmental and political conditions made the region habitable again. At that time, during the Migration Period, "new" Frisians repopulated the coastal regions; these Frisians consisted of tribes with loose bonds, centred without great power. The earliest Frisian records name four social classes, the ethelings and frilings, who together made up the "Free Frisians" who might bring suit at court, the laten or liten with the slaves, who were absorbed into the laten during the Early Middle Ages, as slavery was not so much formally abolished, as evaporated; the laten were tenants of lands they did not own and might be tied to it in the manner of serfs, but in times might buy their freedom. Under the rule of King Aldgisl, the Frisians came in conflict with the Frankish mayor of the palace Ebroin, over the old Roman border fortifications. Aldgisl could keep the Franks at a distance with his army. During the reign of Redbad, the tide turned in favour of the Franks.
In 733, Charles Martel sent an army against the Frisians. The Frisian army was pushed back to Eastergoa; the next year the Battle of the Boarn took place. Charles ferried an army across the Almere with a fleet; the Frisians were defeated in the ensuing battle, their last king Poppo was killed. The victors began burning heathen sanctuaries. Charles Martel returned with much loot, broke the power of the Frisian kings for good; the Franks annexed the Frisian lands between the Vlie and the Lauwers. They conquered the area east of the Lauwers in 785; the Carolingians laid Frisia under the rule of grewan, a title, loosely related to count in its early sense of "governor" rather than "feudal overlord". About 100,000 Dutch drowned in a flood in 1228. When, around 800, the Scandinavian Vikings first attacked Frisia, still under Carolingian rule, the Frisians were released from military service on foreign territory in order to be able to defend themselves against the heathen Vikings. With their victory in the Battle of Norditi in 884 they were able to drive the Vikings permanently out of East Frisia, although it remained under constan
A sluice is a water channel controlled at its head by a gate. A mill race, flume, penstock or lade is a sluice channelling water toward a water mill; the terms sluice, sluice gate, knife gate, slide gate are used interchangeably in the water and wastewater control industry. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway. Sluice gates control water levels and flow rates in rivers and canals, they are used in wastewater treatment plants and to recover minerals in mining operations, in watermills. "Sluice gate" refers to a movable gate allowing water to flow under it. When a sluice is lowered, water may spill over the top. A mechanism drives the sluice up or down; this may be a simple, hand-operated, chain pulled/lowered, worm drive or rack-and-pinion drive, or it may be electrically or hydraulically powered. Flap sluice gate A automatic type, controlled by the pressure head across it, it is a gate hinged at the top. When pressure is from one side, the gate is kept closed.
Vertical rising sluice gate A plate sliding in the vertical direction, which may be controlled by machinery. Radial sluice gate A structure, where a small part of a cylindrical surface serves as the gate, supported by radial constructions going through the cylinder's radius. On occasion, a counterweight is provided. Rising sector sluice gate Also a part of a cylindrical surface, which rests at the bottom of the channel and rises by rotating around its centre. Needle sluice A sluice formed by a number of thin needles held against a solid frame through water pressure as in a needle dam. Fan gate This type of gate was invented by the Dutch hydraulic engineer Jan Blanken in 1808, he was Inspector-General for Waterstaat of the Kingdom of Holland at the time.. The Fan door has the special property that it can open in the direction of high water using water pressure; this gate type was used to purposely inundate certain regions, for instance in the case of the Hollandic Water Line. Nowadays this type of gate can still be found for example in Gouda.
The design of a Fan gate is shown in the image on the left. The sluice has a separate chamber that can be filled with water and is separated on the high-water-level side of the sluice by a large door; when a tube connecting the separate chamber with the high-water-level side of the sluice is opened, the water level, with that the water pressure in this chamber, will rise to the same level as that on the high-water-level side. The surface area of the door separating the chamber from the high-water-level side of the sluice is larger than that of the door closing the sluice. Since pressures are equal this results into a net force. In the mountains of the United States, sluices transported logs from steep hillsides to downslope sawmill ponds or yarding areas. Nineteenth-century logging was traditionally a winter activity for men who spent summers working on farms. Where there were freezing nights, water might be applied to logging sluices every night so a fresh coating of slippery ice would reduce friction of logs placed in the sluice the following morning.
Sluice boxes are used in the recovery of black sands and other minerals from placer deposits during placer mining operations. They may be small-scale, as used in prospecting, or much larger, as in commercial operations, where the material is first screened using a trommel or screening plant. Typical sluices have transverse riffles over a carpet, which trap the heavy minerals and other valuable minerals; the result is a concentrate. Wood Traditionally wood was the material of choice for sluice gates. Cast iron Cast iron has been popular; this material is great at keeping the strength needed. Stainless steel In most cases, stainless steel is lighter than the older cast iron material. Fibre-reinforced plastic In modern times, newer materials such as fibre-reinforced plastic are being used to build sluices; these modern technologies have many of the attributes of the older materials, while introducing advantages such as corrosion resistance and much lighter weights. In the Somerset Levels, sluice gates are known as clyce.
Most of the inhabitants of Guyana refer to sluices as kokers. Sinhala people in Sri Lanka who had an ancient civilization based on harvested rain water, refer to sluices as Horovuwa. Floodgate Gatehouse – An structure to house a sluice gate Lock Zijlstra – A Dutch name referring to one who lives near a sluice Control lock Crittenden, H. Temple; the Maine Scenic Route. McClain Printing. Moody, Linwood W.. The Maine Two-Footers. Howell-North. Cornwall, L. Peter & Farrell, Jack W.. Ride the Sandy River. Pacific Fast Mail. Soar Valley Sluice Gates Salt/Fresh water separating Sluice Complex
Amsterdam is the capital city and most populous municipality of the Netherlands. Its status as the capital is mandated by the Constitution of the Netherlands, although it is not the seat of the government, The Hague. Amsterdam has a population of 854,047 within the city proper, 1,357,675 in the urban area and 2,410,960 in the metropolitan area; the city is located in the province of North Holland in the west of the country but is not its capital, Haarlem. The Amsterdam metropolitan area comprises much of the northern part of the Randstad, one of the larger conurbations in Europe, which has a population of 8.1 million. Amsterdam's name derives from Amstelredamme, indicative of the city's origin around a dam in the river Amstel. Originating as a small fishing village in the late 12th century, Amsterdam became one of the most important ports in the world during the Dutch Golden Age, as a result of its innovative developments in trade. During that time, the city was the leading centre for trade. In the 19th and 20th centuries the city expanded, many new neighbourhoods and suburbs were planned and built.
The 17th-century canals of Amsterdam and the 19–20th century Defence Line of Amsterdam are on the UNESCO World Heritage List. Since the annexation of the municipality of Sloten in 1921 by the municipality of Amsterdam, the oldest historic part of the city lies in Sloten, dating to the 9th century; as the commercial capital of the Netherlands and one of the top financial centres in Europe, Amsterdam is considered an alpha- world city by the Globalization and World Cities study group. The city is the cultural capital of the Netherlands. Many large Dutch institutions have their headquarters there, including Philips, AkzoNobel, TomTom and ING. Many of the world's largest companies are based in Amsterdam or established their European headquarters in the city, such as leading technology companies Uber and Tesla. In 2012, Amsterdam was ranked the second best city to live in by the Economist Intelligence Unit and 12th globally on quality of living for environment and infrastructure by Mercer; the city was ranked 4th place globally as top tech hub in the Savills Tech Cities 2019 report, 3rd in innovation by Australian innovation agency 2thinknow in their Innovation Cities Index 2009.
The Port of Amsterdam to this day remains the second in the country, the fifth largest seaport in Europe. Famous Amsterdam residents include the diarist Anne Frank, artists Rembrandt van Rijn and Vincent van Gogh, philosopher Baruch Spinoza; the Amsterdam Stock Exchange, the oldest stock exchange in the world, is located in the city centre. Amsterdam's main attractions include its historic canals, the Rijksmuseum, the Van Gogh Museum, the Stedelijk Museum, Hermitage Amsterdam, the Anne Frank House, the Scheepvaartmuseum, the Amsterdam Museum, the Heineken Experience, the Royal Palace of Amsterdam, Natura Artis Magistra, Hortus Botanicus Amsterdam, NEMO, the red-light district and many cannabis coffee shops, they draw more than 5 million international visitors annually. The city is well known for its nightlife and festival activity, it is one of the world's most multicultural cities, with at least 177 nationalities represented. After the floods of 1170 and 1173, locals near the river Amstel built a bridge over the river and a dam across it, giving its name to the village: "Aemstelredamme".
The earliest recorded use of that name is in a document dated 27 October 1275, which exempted inhabitants of the village from paying bridge tolls to Count Floris V. This allowed the inhabitants of the village of Aemstelredamme to travel through the County of Holland, paying no tolls at bridges and dams; the certificate describes the inhabitants. By 1327, the name had developed into Aemsterdam. Amsterdam is much younger than Dutch cities such as Nijmegen and Utrecht. In October 2008, historical geographer Chris de Bont suggested that the land around Amsterdam was being reclaimed as early as the late 10th century; this does not mean that there was a settlement since reclamation of land may not have been for farming—it may have been for peat, for use as fuel. Amsterdam was granted city rights in either 1300 or 1306. From the 14th century on, Amsterdam flourished from trade with the Hanseatic League. In 1345, an alleged Eucharistic miracle in the Kalverstraat rendered the city an important place of pilgrimage until the adoption of the Protestant faith.
The Miracle devotion was kept alive. In the 19th century after the jubilee of 1845, the devotion was revitalized and became an important national point of reference for Dutch Catholics; the Stille Omgang—a silent walk or procession in civil attire—is the expression of the pilgrimage within the Protestant Netherlands since the late 19th century. In the heyday of the Silent Walk, up to 90,000 pilgrims came to Amsterdam. In the 21st century this has reduced to about 5000. In the 16th century, the Dutch rebelled against Philip II of his successors; the main reasons for the uprising were the imposition of new taxes, the tenth penny, the religious persecution of Protestants by the newly introduced Inquisition. The revolt escalated into the Eighty Years' War, which led to Dutch independence. Pushed by Dutch Revolt leader William the Silent, the Dutch Republic became known for its relative religious tolerance. Jews from the Iberian Peninsula, Huguenots from France, prosperous merchants and printers from Flanders, economic and religious refugees
Willows called sallows and osiers, form the genus Salix, around 400 species of deciduous trees and shrubs, found on moist soils in cold and temperate regions of the Northern Hemisphere. Most species are known as willow, but some narrow-leaved shrub species are called osier, some broader-leaved species are referred to as sallow; some willows are creeping shrubs. Willows all have abundant watery bark sap, charged with salicylic acid, soft pliant, tough wood, slender branches, large, fibrous stoloniferous roots; the roots are remarkable for their toughness and tenacity to live, roots sprout from aerial parts of the plant. The leaves are elongated, but may be round to oval with serrated edges. Most species are deciduous. All the buds are lateral; the buds are covered by a single scale. The bud scale is fused into a cap-like shape, but in some species it wraps around and the edges overlap; the leaves are simple, feather-veined, linear-lanceolate. They are serrate, rounded at base, acute or acuminate; the leaf petioles are short, the stipules very conspicuous, resembling tiny, round leaves, sometimes remaining for half the summer.
On some species, they are small and caducous. In color, the leaves show a great variety of greens. Willows are dioecious, with male and female flowers appearing as catkins on separate plants; the staminate flowers are without either calyx with corolla. This scale is square and hairy; the anthers are orange or purple after the flower opens. The filaments are threadlike pale brown, bald; the pistillate flowers are without calyx or corolla, consist of a single ovary accompanied by a small, flat nectar gland and inserted on the base of a scale, borne on the rachis of a catkin. The ovary is one-celled, the style two-lobed, the ovules numerous. All willows take root readily from cuttings or where broken branches lie on the ground; the few exceptions include the goat peachleaf willow. One famous example of such growth from cuttings involves the poet Alexander Pope, who begged a twig from a parcel tied with twigs sent from Spain to Lady Suffolk; this twig was planted and thrived, legend has it that all of England's weeping willows are descended from this first one.
Willows are planted on the borders of streams so their interlacing roots may protect the bank against the action of the water. The roots are much larger than the stem which grows from them. Willows have a wide natural distribution from the tropics to the arctic zones and are extensively cultivated around the world. Willows are cross-compatible, numerous hybrids occur, both and in cultivation. A well-known ornamental example is the weeping willow, a hybrid of Peking willow from China and white willow from Europe; the hybrid cultivar'Boydii' has gained the Royal Horticultural Society's Award of Garden Merit. Numerous cultivars of Salix L. have been named over the centuries. New selections of cultivars with superior technical and ornamental characteristics have been chosen deliberately and applied to various purposes. Most Salix has become an important source for bioenergy production and for various ecosystem services; the first edition of the Checklist for Cultivars of Salix L. was compiled in 2015, which includes 854 cultivar epithets with accompanying information.
The International Poplar Commission of the FAO UN holds the International Cultivar Registration Authority for the genus Salix. The ICRA for Salix produces and maintains The International Register of Cultivars of Salix L.. Willows are used as food plants by the larvae of some Lepidoptera species, such as the mourning cloak butterfly. Ants, such as wood ants, are common on willows inhabited by aphids, coming to collect aphid honeydew, as sometimes do wasps. A small number of willow species were planted in Australia, notably as erosion-control measures along watercourses, they are now regarded as invasive weeds which occupy extensive areas across southern Australia and are considered'Weeds of National Significance'. Many catchment management authorities are replacing them with native trees. Substantial research undertaken from 2006 has identified that willows inhabit an unoccupied niche when they spread across the bed of shallow creeks and streams and if removed, there is a potential water saving of up to 500 ML/per year per hectare of willow canopy area, depending on willow species and climate zone.
This water could benefit the environment or provision of local water resources during dry periods. To aid management of willows, a remote sensing method has been developed to map willow area along and in streams a
The North Sea is a marginal sea of the Atlantic Ocean located between the United Kingdom, Norway, Germany, the Netherlands and France. An epeiric sea on the European continental shelf, it connects to the ocean through the English Channel in the south and the Norwegian Sea in the north, it is more than 970 kilometres long and 580 kilometres wide, with an area of 570,000 square kilometres. The North Sea has long been the site of important European shipping lanes as well as a major fishery; the sea is a popular destination for recreation and tourism in bordering countries and more has developed into a rich source of energy resources including fossil fuels and early efforts in wave power. The North Sea has featured prominently in geopolitical and military affairs in Northern Europe, it was important globally through the power northern Europeans projected worldwide during much of the Middle Ages and into the modern era. The North Sea was the centre of the Vikings' rise. Subsequently, the Hanseatic League, the Netherlands, the British each sought to dominate the North Sea and thus access to the world's markets and resources.
As Germany's only outlet to the ocean, the North Sea continued to be strategically important through both World Wars. The coast of the North Sea presents a diversity of geographical features. In the north, deep fjords and sheer cliffs mark the Norwegian and Scottish coastlines, whereas in the south, the coast consists of sandy beaches and wide mudflats. Due to the dense population, heavy industrialization, intense use of the sea and area surrounding it, there have been various environmental issues affecting the sea's ecosystems. Adverse environmental issues – including overfishing and agricultural runoff and dumping, among others – have led to a number of efforts to prevent degradation of the sea while still making use of its economic potential; the North Sea is bounded by the Orkney Islands and east coast of Great Britain to the west and the northern and central European mainland to the east and south, including Norway, Germany, the Netherlands and France. In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean.
In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively. In the north it is bordered by the Shetland Islands, connects with the Norwegian Sea, which lies in the north-eastern part of the Atlantic; the North Sea is more than 970 kilometres long and 580 kilometres wide, with an area of 570,000 square kilometres and a volume of 54,000 cubic kilometres. Around the edges of the North Sea are sizeable islands and archipelagos, including Shetland and the Frisian Islands; the North Sea receives freshwater from a number of European continental watersheds, as well as the British Isles. A large part of the European drainage basin empties into the North Sea, including water from the Baltic Sea; the largest and most important rivers flowing into the North Sea are the Elbe and the Rhine – Meuse watershed. Around 185 million people live in the catchment area of the rivers discharging into the North Sea encompassing some industrialized areas.
For the most part, the sea lies on the European continental shelf with a mean depth of 90 metres. The only exception is the Norwegian trench, which extends parallel to the Norwegian shoreline from Oslo to an area north of Bergen, it has a maximum depth of 725 metres. The Dogger Bank, a vast moraine, or accumulation of unconsolidated glacial debris, rises to a mere 15 to 30 m below the surface; this feature has produced the finest fishing location of the North Sea. The Long Forties and the Broad Fourteens are large areas with uniform depth in fathoms; these great banks and others make the North Sea hazardous to navigate, alleviated by the implementation of satellite navigation systems. The Devil's Hole lies 200 miles east of Scotland; the feature is a series of asymmetrical trenches between 20 and 30 kilometres long and two kilometres wide and up to 230 metres deep. Other areas which are less deep are Fisher Bank and Noordhinder Bank; the International Hydrographic Organization defines the limits of the North Sea as follows: On the Southwest.
A line joining the Walde Lighthouse and Leathercoat Point. On the Northwest. From Dunnet Head in Scotland to Tor Ness in the Island of Hoy, thence through this island to the Kame of Hoy on to Breck Ness on Mainland through this island to Costa Head and to Inga Ness in Westray through Westray, to Bow Head, across to Mull Head and on to Seal Skerry and thence to Horse Island. On the North. From the North point of the Mainland of the Shetland Islands, across to Graveland Ness in the Island of Yell, through Yell to Gloup Ness and across to Spoo Ness in Unst island, through Unst to Herma Ness, on to the SW point of the Rumblings and to Muckle Flugga all these being included in the North Sea area.
Mean sea level is an average level of the surface of one or more of Earth's oceans from which heights such as elevation may be measured. MSL is a type of vertical datum – a standardised geodetic datum –, used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and aircraft flight levels. A common and straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied over geological time scales; however 20th century and current millennium sea level rise is caused by global warming, careful measurement of variations in MSL can offer insights into ongoing climate change. The term above sea level refers to above mean sea level. Precise determination of a "mean sea level" is difficult to achieve because of the many factors that affect sea level. Instantaneous sea level varies quite a lot on several scales of space.
This is because the sea is in constant motion, affected by the tides, atmospheric pressure, local gravitational differences, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. Still-water level or still-water sea level is the level of the sea with motions such as wind waves averaged out. MSL implies the SWL further averaged over a period of time such that changes due to, e.g. the tides have zero mean. Global MSL refers to a spatial average over the entire ocean. One measures the values of MSL in respect to the land. In the UK, the Ordnance Datum is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the vertical datum was MSL at the Victoria Liverpool. Since the times of the Russian Empire, in Russia and other former its parts, now independent states, the sea level is measured from the zero level of Kronstadt Sea-Gauge.
In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 1.230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collapsed data about the sea level, it is used for main part of Africa as official sea level. As for Spain, the reference to measure heights below or above sea level is placed in Alicante. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, which dates back to the 1690s. Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008. Height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum, it is used in aviation, where some heights are recorded and reported with respect to mean sea level, in the atmospheric sciences, land surveying.
An alternative is to base height measurements on an ellipsoid of the entire Earth, what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is used to define heights; the alternative is to use a geoid-based vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, variations in elevation are shown by contour lines; the elevation of a mountain denotes the highest point or summit and is illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, the elevation AMSL is negative. For one such case, see Amsterdam Airport Schiphol. To extend this definition far from the sea means comparing the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called the geoid. In a state of rest or absence of external forces, the mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field.
In reality, due to currents, air pressure variations and salinity variations, etc. this does not occur, not as a long-term average. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as ocean surface topography, it varies globally in a range of ± 2 m. Adjustments were made to sea-level measurements to take into account the effects of the 235 lunar month Metonic cycle and the 223-month eclipse cycle on the tides. Several terms are used to describe the changing relationships between sea level and dry land; when the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps; the term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in
The Wadden Sea is an intertidal zone in the southeastern part of the North Sea. It lies between the coast of northwestern continental Europe and the range of low-lying Frisian Islands, forming a shallow body of water with tidal flats and wetlands, it is an important area for both breeding and migrating birds. In 2009, the Dutch and German parts of the Wadden Sea were inscribed on UNESCO's World Heritage List and the Danish part was added in June 2014; the Wadden Sea stretches from Den Helder, in the northwest of the Netherlands, past the great river estuaries of Germany to its northern boundary at Skallingen in Denmark along a total coastline of some 500 km and a total area of about 10,000 km2. Within the Netherlands it is bounded from the IJsselmeer by the Afsluitdijk; the Wadden Sea's coastline has been modified by man. Extensive systems of dikes and causeways make it among the most human-altered on the planet; the word wad is Dutch for "mud flat". The area is typified by extensive tidal mud flats, deeper tidal trenches and the islands that are contained within this, a region continually contested by land and sea.
The landscape has been formed for a great part by storm tides in the 10th to 14th centuries and carrying away former peat land behind the coastal dunes. The present islands are a remnant of the former coastal dunes. Towards the North Sea the islands are marked by dunes and wide sandy beaches, towards the Wadden Sea a low, tidal coast; the impact of waves and currents carrying away sediments is changing both land masses and coastlines. For example, the islands of Vlieland and Ameland have moved eastwards through the centuries, having lost land on one side and added it on the other; the Wadden Sea is famous for its rich flora and fauna birds. Hundreds of thousands of waders and geese use the area as a migration stopover or wintering site, it is a rich habitat for gulls and terns. However, the biodiversity of Wadden Sea today is only a fraction of what was seen before human exploitation; some regionally extinct species are still found here. According to J. B. MacKinnon, larger fish including sturgeons, Atlantic salmon, brown trout, others like lacuna snails and oyster beds that were once found elsewhere in the region have disappeared as the Wadden Sea has been reduced to about 50% of its original size and nutrients from Rhine river no longer flow into it.
As a result, about 90% of all the species which inhabited the Wadden Sea are present at risk. Wadden Sea is an important habitat for grey seals. Harbour porpoises and Atlantic white-beaked dolphins, which once were locally extinct but have re-colonized the area, are the sea's only resident cetaceans. Many other species have disappeared, only visit seasonally, or occasionally. North Atlantic right whales and gray whales were once seen in the region, using the shallow, calm waters for either feeding and breeding, before they were wiped out by shore-based whaling, they are now thought to either have remnant populations In the low-tens. A possible right whale was observed close to beaches on Texel in the West Frisian Islands and off Steenbanken, Schouwen-Duiveland in July 2005. Recent increases in number of North Atlantic humpback whales and minke whales might have resulted in more visits and possible re-colonization by the species to the areas around Marsdiep. Future recovery of once-extinct local bottlenose dolphins is expected.
A number of human-introduced invasive species, including algae and smaller organisms, are causing negative effects on native species. Each of three countries has designated Ramsar sites in the region. Although the Wadden Sea is not yet listed as a transboundary Ramsar site, a great part of the Wadden Sea is protected in cooperation of all three countries; the governments of the Netherlands and Germany have been working together since 1978 on the protection and conservation of the Wadden Sea. Co-operation covers management and research, as well as political matters. Furthermore, in 1982, a Joint Declaration on the Protection of the Wadden Sea was agreed upon to co-ordinate activities and measures for the protection of the Wadden Sea. In 1997, a Trilateral Wadden Sea Plan was adopted. In 1986, the Wadden Sea Area was declared a biosphere reserve by UNESCO. In June 2009, the Wadden Sea was placed on the World Heritage list by UNESCO; the Danish part was added to the site in 2014. Many of the islands have been popular seaside resorts since the 19th century.
Mudflat hiking, i.e. walking on the sandy flats at low tide, has become popular in the Wadden Sea. It is a popular region for pleasure boating; the German part of the Wadden Sea was the setting for the 1903 Erskine Childers novel The Riddle of the Sands. Vollmer, M.. "Landscape and Cultural Heritage in the Wadden Sea Region - Project Report". Wadden Sea Ecosystem. 12. Knottnerus, Otto S.. "History of human settlement, cultural change and interference with the marine environment". Secretariat of The Trilateral Cooperation on the Protection of the Wadden Sea Official Tourist Information for the northernmost part of the national park: The Danish Wadden Sea Official Tourist Information for the western