Misplaced Pages

#774225

59-490: Washdyke Lagoon is a brackish shallow coastal lagoon approximately 1 kilometre (0.62 mi) north of Timaru , South Canterbury , New Zealand . The lagoon has drastically reduced in size since 1881 when it was approximately 253 hectares (630 acres), now it is less than 48 hectares (0.48 km) in area. It is enclosed by a barrier beach that is 3 kilometres (1.9 mi) long and 3 metres (9.8 ft) above high tide at its largest point (see Figure 1). The reduced lagoon size

118-430: A combination of an existing seawall and new gravel dredging to form a harbour from 1986 to 1902, caused the erosion of the whole village by 1917. This was due to sediment starvation causing the erosion of the mixed sand and gravel barrier beaches which protected the village. They are not alone, the effects of man-made structures on restricting or diverting natural sediment transport are now well known and to some extent there

177-427: A feeding ground for a variety of birds including waterfowl, handfuls of migratory godwits and sandpipers , herons and other species of water birds (Figure 5). Gulls and dotterels nest on the shingle barrier of the eastern side. However, in recent years black-fronted dotterel numbers have been declining. Saltmarsh ribbonwood, rushes and exotic plants can be found on the margins of the lagoon. A reef borders part of

236-486: A healthy natural ecosystem, especially fish and wildlife habitat, and a decrease in the number of people participating in trout fishing and other activities has been recorded since 1996. In a 2010 report on lake water quality Lake Ellesmere / Te Waihora was deemed the second most polluted lake in New Zealand in terms of nutrient content and algal growth. Algal blooms are a regular summer occurrence and toxic algae bloomed in

295-523: A lake is hu ( 湖 ), and a lagoon is xihu ( 潟湖 ). In the French Mediterranean several lagoons are called étang ("lake"). Contrariwise, several other languages have specific words for such bodies of water. In Spanish, coastal lagoons generically are laguna costera , but those on the Mediterranean coast are specifically called albufera . In Russian and Ukrainian, those on

354-555: A length of the Washdyke Barrier to be renourished in order to protect a sewage outfall pipe and ascertain whether or not the system would viably protect the barrier structure. A 300 metres (980 ft) section of the barrier was raised 2–2.5 metres (6 ft 7 in – 8 ft 2 in) using sediments which have rolled over the barrier and are now on the lagoon side, then armouring them with coarse sediments brought in from Opihi River (12 kilometres (7.5 mi) away). Despite

413-422: A regular flow of fresh water an "estuary". Davis does state that the terms "lagoon" and "estuary" are "often loosely applied, even in scientific literature". Timothy M. Kusky characterizes lagoons as normally being elongated parallel to the coast, while estuaries are usually drowned river valleys, elongated perpendicular to the coast. Coastal lagoons are classified as inland bodies of water. When used within

472-442: Is a brackish bar-type waterbody, commonly called a lake or lagoon . It covers an area of 198 square kilometres (76 sq mi), and is New Zealand's 5th largest lake (by area). This illustrates why Lake Ellesmere / Te Waihora has undergone significant ecological transformation in recent years as land use practices in the catchment area have changed. Southern elephant seals have been observed here, spending short periods in

531-419: Is a large amount of coarse grained sediments available and storm wave conditions during which more sediment load is transported ashore. They also form steep slopes in high wave energy environments and have very high levels of seepage of freshwater into the ocean, due to the large grain size range increasing permeability. Another characteristic is the zonation of sediments on the barrier. Coarse, flat sediments form

590-453: Is actually the third-largest lake by area in the country. The brackish water lagoon may be thus explicitly identified as a "coastal lagoon" ( laguna costera ). In Portuguese, a similar usage is found: lagoa may be a body of shallow seawater, or a small freshwater lake not linked to the sea. Lagoon is derived from the Italian laguna , which refers to the waters around Venice ,

649-501: Is also possible that it will permanently breach forming an open bay in the coming decades. Waituna Lagoon is also under threat from breaching but in this case it is machinery not erosion that is opening the coastal lake to the ocean. This is so that it can be used for hunting and allow grazing at its banks. However, it is now been opened more frequently increasing the natural salinity of the lagoon. The effects of this on native fish and bird species are still not fully understood. Currently

SECTION 10

#1733114988775

708-469: Is due to the construction of the Timaru Port breakwater which is preventing coarse sediments from reaching and replenishing Washdyke Barrier. This is important as the lagoon and the surrounding 250 hectares (620 acres) are classified as a wildlife refuge and it demonstrates the role human structures have on coastline evolution. Washdyke Lagoon is a coastal lake, ‘choked’ type lagoon as it is separated from

767-492: Is now a move away from these. There is also an issue surrounding the pollution of the lagoon. Nearby freezing works have previously pumped waste water into the lagoon. Workers in charge of checking this discharge pipe also noted thinning of the barrier as early as 1897. More recently there has been concern about the pollution runoff from the Washdyke industrial area immediately to the west of the lagoon. Another source of pollutants

826-612: The Black Sea are liman ( лиман ), while the generic word is laguna ( Лагуна ). Similarly, in the Baltic , Danish has the specific Nor  [ da ] , and German the specifics Bodden and Haff , as well as generic terms derived from laguna . In Poland these lagoons are called zalew ("bay"), in Lithuania marios ("lagoon, reservoir"). In Jutland several lagoons are known as fjord . In New Zealand

885-523: The Māori word hapua refers to a coastal lagoon formed at the mouth of a braided river where there are mixed sand and gravel beaches, while waituna , an ephemeral coastal waterbody, is neither a true lagoon, lake nor estuary. Some languages differentiate between coastal and atoll lagoons. In French, lagon  [ fr ] refers specifically to an atoll lagoon, while coastal lagoons are described as étang  [ fr ] ,

944-592: The Venetian Lagoon . Laguna is attested in English by at least 1612, and had been Anglicized to "lagune" by 1673. In 1697 William Dampier referred to a "Lagune or Lake of Salt water" on the coast of Mexico. Captain James Cook described an island "of Oval form with a Lagoon in the middle" in 1769. Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only

1003-452: The Wadden Sea , have strong tidal currents and mixing. Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide. Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands. Mangroves and marsh plants can facilitate

1062-422: The accretion of sediment to at least equal the rate of erosion in order for the lagoon to remain separate from the ocean. This balance is also effected by sea level changes, rising causing the barrier to be overtopped and falling allowing a smaller barrier keep the lagoon separate. There are many examples of these relatively closed lagoon systems around the world. Most have significant ecological value, so preserving

1121-680: The accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments. Lake Ellesmere Lake Ellesmere / Te Waihora is a broad, shallow coastal lake or waituna , in the Canterbury region of the South Island of New Zealand. It is directly to the west of Banks Peninsula , separated from the Pacific Ocean by the long, narrow, sandy Kaitorete Spit , or more correctly Kaitorete Barrier. It lies partially in extreme southeastern Selwyn District and partially in

1180-469: The balance between fresh and salt water is important. Examples include the Coorong , Australia, 260 square kilometres (100 sq mi), Laguna de Araruama (Brazil, 10,360 square kilometres (4,000 sq mi)), Lake St. Lucia (South Africa, 312 square kilometres (120 sq mi)) and Lake Songkhla (Thailand, 1,040 square kilometres (400 sq mi)). If the sediment sources for these barriers

1239-413: The barrier and push sediment from the ocean side to the lagoon side, there is no incoming sediment on the ocean side to rebuild the barrier. This means that the barrier migrate landward as the barrier ridges are reworked. The ratio of fine to coarse sediments making up the barrier is also increased. The coarse sediments armour the barrier structure against ocean swell and wind waves , without this sediment

SECTION 20

#1733114988775

1298-515: The coast down braided rivers that originated at the Southern Alps and fine sediments from further offshore. Southerly currents push them north and they are then deposited on Washdyke Barrier causing it to stay above the high tide mark and form the lagoon. The southerly current travelling up from south of the South Island of New Zealand has formed a chain of lagoons along the east and south coast of

1357-571: The coast just off the barrier, attracting oystercatchers and turnstones . The area is also popular for catching whitebait off the barrier. The ecology of lagoon systems is lost if the sediment sources for these barriers is removed and their barriers erode away, bays then form in the lagoons place with inundation. This is what will happen at Washdyke Lagoon and other lagoons around the world if human activities continue to starve natural sediment supplies. This will have ecological implications and will also allow for flooding of land previously protected by

1416-451: The coast to the south of the port is accumulating sediment forming 80 hectare of new land. This is a large loss to the north of the port that can not be replaced by current longshore transport mechanisms. The port's breakwater starves the barrier of coarse sediments from the rivers to the south. As shown in Figure 4, prior to breakwater construction fine and coarse sediments were transported from

1475-614: The context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area. Many lagoons do not include "lagoon" in their common names. Currituck , Albemarle and Pamlico Sounds in North Carolina , Great South Bay between Long Island and the barrier beaches of Fire Island in New York , Isle of Wight Bay , which separates Ocean City, Maryland from

1534-532: The crest, whilst large, spherical and rod shape sediments form the outer part and the barrier infill is made up of finer sediment sizes. Washdyke Lagoon is a useful example of a barrier that displays all of these characteristics. The lagoon is situated at the southern end of the Canterbury Bight . This coastline is characterised by its mixed sand and gravel beaches and southerly longshore currents. These currents transport coarse greywacke sediments that have reached

1593-520: The cultural health of Lake Ellesmere / Te Waihora was undertaken as a combined effort by Ngai Tahu and the National Institute of Water and Atmospheric Research (NIWA). As well as holding high cultural significance to the indigenous population Lake Ellesmere / Te Waihora is also rated as a nationally significant site for recreation. The lake is currently used for a wide range of water and land based activities. Many of these activities are reliant on

1652-429: The end of large river mouths. Lagoons form when longshore transport builds up sediment across the mouth of a water source cutting it off or diverting it from directly reaching the ocean. In order for a lagoon to form the barrier needs both a coarse and fine sediment source, the fines usually from longshore transport offshore and the coarse usually from transport of sediment from river mouths. The barriers created rely on

1711-408: The fines are much more vulnerable to being removed leaving the barrier structure more vulnerable. Maximum wave height for this section of coast during one October was found to be 6.3 metres (21 ft), and other studies have recorded frequent breakers around 5 metres (16 ft) high. This means that the barrier would frequently have to deal with overtopping events. Another factor that is preventing

1770-583: The generic word for a still lake or pond. In Vietnamese, Đầm san hô refers to an atoll lagoon, whilst Đầm phá is coastal. In Latin America, the term laguna in Spanish, which lagoon translates to, may be used for a small fresh water lake in a similar way a creek is considered a small river. However, sometimes it is popularly used to describe a full-sized lake , such as Laguna Catemaco in Mexico, which

1829-414: The island, including Waituna , Wainono and Washdyke Lagoons, Coopers Lagoon / Muriwai , and Lake Ellesmere / Te Waihora . Like Washdyke, these closed lagoons are also facing the possibility of becoming much more open systems in the near future. Currently Kaitorete Spit (enclosing Lake Ellesmere / Te Waihora) is undergoing erosion, especially at its southern end, due to coastal rotation of currents. It

Washdyke Lagoon - Misplaced Pages Continue

1888-496: The lagoon began to erode rapidly after the construction of the port resulting in the complete destruction of the lagoon, leaving behind an open bay in its place. Internationally, sediment starvation is causing the erosion of many important coastal features. Breakwaters and other man-made structures in Thailand are responsible for accelerated beach erosion which may start to affect tourism in the coming years. In Hallsands, Devon, England,

1947-410: The lagoon is shrinking at an alarming rate. The barrier has retreated 400 metres (1,300 ft) between 1865 and 1987 (3.2 metres (10 ft) per year). In 1992 it was predicted that by the year 2000 the lagoon would have totally disappeared. Whilst this has not yet happened it is still a possibility in the near future. This would cause flooding of the Washdyke industrial area and the loss of habitat for

2006-638: The lagoon, such as the Washdyke industrial area. Lagoon Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposed shoal , coral reef , or similar feature. Some authorities include fresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree of salinity . The distinction between "lagoon" and "estuary" also varies between authorities. Richard A. Davis Jr. restricts "lagoon" to bodies of water with little or no fresh water inflow, and little or no tidal flow, and calls any bay that receives

2065-611: The lagoon. Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, such as Lake St. Lucia , in South Africa , may become highly saline. Lagoons with no connection to the open ocean and significant inflow of fresh water, such as the Lake Worth Lagoon in Florida in the middle of the 19th century, may be entirely fresh. On the other hand, lagoons with many wide inlets, such as

2124-618: The lake and its surroundings, including native species such as the Pied Stilt , South Island Pied Oystercatcher , Banded Dotterel and Wrybill , and also Arctic migrants such as the Bar-Tailed Godwit , Red-Necked Stint , Sharp-Tailed Sandpiper and Pacific Golden Plover , among others. Waterfowl are also prominent residents on the lake, with native species including Paradise Shelduck , New Zealand Scaup , Australasian Shoveler and Grey Teal . Grey Teal are actually considered one of

2183-501: The lake as part of Canterbury plains, which were then flooded, forming a bay, then an estuary and finally a lake / lagoon / waituna. Lake Ellesmere / Te Waihora has been a revered mahinga kai (site of traditional significance for food and other natural resources) for Māori since ancient times and remains central to the lives of many Māori who now live in the area. Under the Ngāi Tahu Claims Settlement 1998, ownership of

2242-489: The lake bed of Lake Ellesmere / Te Waihora was returned to Te Rūnanga O Ngāi Tahu, who are now able to reassert their rangatiratanga (ownership) over this significant site through direct control of its management. The traditional name for the lake was Te Kete Ika o Rākaihautū meaning "the fish basket of Rākaihautū ". The food sources of Lake Ellesmere / Te Waihora were once abundant and included tuna (eels), pātiki (flounder) and aua (mullet). Lake Ellesmere / Te Waihora

2301-583: The lake, as can some tern species such as the Caspian Tern , White-Fronted Tern and Black-Fronted Tern , and the rarer White-Winged Tern . A wide variety of other birds can also be seen in and around the lake, including White-Faced Heron , Eastern Cattle Egret , Royal Spoonbill , Australasian Harrier , Pukeko , Spotless Crake , Sacred Kingfisher , as well as various introduced Galliforms and both native and introduced Passerines . A variety of rare vagrant birds have also appeared at Lake Ellesmere over

2360-506: The lake. Basking sharks have occasionally entered the lake. Lake Ellesmere is also home to a wide variety of birds , with over 200 species (if extinct species are also included) having been recorded at the lake and its direct surroundings. Lake Ellesmere has become a well-known bird watching location for certain rare species, such as the Australasian Bittern , Marsh Crake and Kotuku . Wading birds of various species frequent

2419-556: The land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep underwater to protect the lagoon. Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of

Washdyke Lagoon - Misplaced Pages Continue

2478-486: The most abundant bird species on the lake. Introduced waterfowl species include Mallards , feral Greylag Geese , Canada Geese , Mute Swan and Black Swan , with the latter being another one of the lake's most abundant birds. Cormorants / Shags such as the Black Shag , Pied Shag and Little Shag are commonly seen in the lake. Black-Backed Gull , Red-Billed Gull and Black-Billed Gull can be seen in and around

2537-423: The overall findings of the report being that the project was 'technically and economically feasible' no further renourishment work of the barrier has been undertaken. However, the effects of the renourishment on this section of the barrier is still evident (as of 2006). Further work is needed in order to show the best way to maintain the bar economically and environmentally. This work needs to be site specific due to

2596-407: The reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20 m (66 ft)) portions. Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop offshore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or subsidence of

2655-606: The rest of Worcester County, Maryland , Banana River in Florida , US, Lake Illawarra in New South Wales , Australia, Montrose Basin in Scotland , and Broad Water in Wales have all been classified as lagoons, despite their names. In England, The Fleet at Chesil Beach has also been described as a lagoon. In some languages the word for a lagoon is simply a type of lake: In Chinese

2714-434: The sea by a built-up bar, and has only minimal tidal input (<5% of total tidal impact to coast within the lagoon). Lagoons of this type usually form along high energy, microtidal coastlines, have high ratio of fresh to salt water and rarely open to the ocean. This type of lagoon differs from more ‘open’ lagoons which are open to the ocean through one or more channels, have a lower percentage of fresh water and form directly at

2773-420: The south and deposited on Washdyke Barrier. However, after the breakwater was built the coarse sediment is unable to reach the barrier as it accumulates at the port's southern side. Some sediment is supplied further offshore by bypassing the breakwater but this is a much reduced load. Without sediment supply erosion of the barrier is rapid as normal processes such as washover continue. This happens when waves hit

2832-407: The southwestern extension of the former Banks Peninsula District, which now (since 2006) is a ward in the city of Christchurch . The lake holds high historical and cultural significance to the indigenous Māori population and the traditional Māori name Te Waihora , means spreading waters . It has officially had a dual English/Māori name since at least 1938. Currently Lake Ellesmere / Te Waihora

2891-477: The supply of coarse sediment to the lagoon barrier is the damming of the Waitaki River . The dam was constructed by 1934 as part of a hydroelectric scheme and is the only braided river in New Zealand that is dammed. It is estimated that the dam stops 50% of the bed load transport. The amount of sediment that is supplied to the barrier is the most important aspect in determining barrier alignment and breakdown. This

2950-400: The unique morphodynamics and challenges that the lagoon is facing. Mixed sand and gravel barriers are an area that is being continuously studied and some long term behaviours are still not understood. A challenge to future work is that the Timaru Port is a major economic driver in the region and sections of the community may feel that Washdyke Lagoon is a necessary sacrifice. Washdyke Lagoon is

3009-594: The wildlife within the refuge. The drastic reduction in area of the lagoon can be at least partially attributed to the construction of the Timaru Port, which started in 1878. In building the port's 700 metres (2,300 ft) long breakwater (Figure 3) the sediment supply from the south is blocked from reaching the Washdyke Lagoon area. Since the construction the Washdyke-Opihi coast has lost 2,620,000 cubic metres (93,000,000 cu ft) of sediment per year, whilst

SECTION 50

#1733114988775

3068-510: The world's shorelines. In the United States, lagoons are found along more than 75 percent of the Eastern and Gulf Coasts . Coastal lagoons can be classified as leaky, restricted, or choked. Coastal lagoons are usually connected to the open ocean by inlets between barrier islands. The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of

3127-454: The years, with some of these including Little Stint , Long-Toed Stint , Stilt Sandpiper , and most notably Cox's Sandpiper . Australian Terns are also rare visitors to the lake. The lake is a dynamic feature, it has been up to twice its present depth and area in the past, and it has progressed through various stages as it has developed into the brackish bar-type lagoon that we see today. In chronological order these stages began with

3186-410: Was a famed mahinga manu wai māori (place for taking waterfowl). However, today the richness of Lake Ellesmere / Te Waihora as a mahinga kai has been largely lost to farmland. While it remains a mahinga kai , its yields have been significantly reduced due to the periodic drainage of the lake in order to maintain reclaimed land and pasture. In the pre-Pākehā past however, the control of the lake's level

3245-470: Was proven that 20% of these tailings are coarse enough to benefit Washdyke Barrier, so tailings have been dumped off the Washdyke coast since the early 1990s. However 80% of this material is unsuitable due to the fine, weathered nature of the sediments, making them less resistant to wave activity than the sediment source prior to port construction. From 1979 to 1985 the Timaru City Council commissioned

3304-484: Was retained at an optimum water level for the birdlife that lived there and provided kai (food) for many people. The lake was only drained when its level exceeded the normal maximum. Kōrari ( flax stalks) were dragged across the sand to make the initial opening of the water to the sea. Such carefully monitored drainage of the lake took place for several hundred years, consistently maintaining Lake Ellesmere / Te Waihora's abundant supply of kai . In 2007 an assessment of

3363-515: Was shown studying the coastal barriers on the Atlantic coast of Nova Scotia. This is particularly important as these barriers are one of the few other MSG beaches internationally. Another, more local site very relevant to the issues at Washdyke Lagoon is Waimataitai Lagoon. This lagoon was situated just north of the Port of Timaru (South of Washdyke Lagoon and Dashing Rocks) prior to 1933. The barrier enclosing

3422-510: Was the sewage outfall pipe which ended on the ocean side of the middle of the barrier and was in use until 1998. This pipe was constantly at risk to exposure and damage as the barrier eroded and would have contributed pollutants and caused nitrification in the lagoon. Every ten months the entrance to the Timaru Port is dredged in order to keep the channel deep enough for use as a commercial port. Each time around 100,000 cubic metres (3,500,000 cu ft) of fine grained sediments are removed. It

3481-490: Was to be removed their barriers would be eroded away and bays would form in the lagoons place with inundation. Washdyke Lagoon was created by the formation of a mixed sand and gravel (MSG) beach barrier (Figure 2) allowing fluvial water from Washdyke Creek to accumulate behind it, with some tidal infiltration through the barrier. The MSG barrier type is relatively rare and has its own unique set of processes and morphology. MSG barriers form mostly on paraglacial coasts where there

#774225