Shoal

In oceanography, geomorphology, and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.[1][2]

The term shoal is also used in a number of ways that can be either similar or quite different from how it is used in the geologic, geomorphic, and oceanographic literature. Sometimes, this terms refers to either any relatively shallow place in a stream, lake, sea, or other body of water; a rocky area on the sea floor within an area mapped for navigation purposes; a growth of vegetation on the bottom of a deep lake that occurs at any depth; and as a verb for the process of proceeding from a greater to a lesser depth of water.[2]

GughSandbar
Sandbar between St Agnes and Gugh on the Isles of Scilly, off the coast of Cornwall, England, United Kingdom.
WayaWayasewa
A tidal sandbar connecting the islands of Waya and Wayasewa of the Yasawa Islands, Fiji.
Nosy Iranja 097
Sandbar between Nosy Iranja Be and Nosy Iranja Kely
(Nosy Iranja, Madagascar)

Description

Shoals are characteristically long and narrow (linear) ridges. They can develop where a stream, river, or ocean current promotes deposition of sediment and granular material, resulting in localized shallowing (shoaling) of the water. Marine shoals also develop either by the in place drowning of barrier islands as the result of episodic sea level rise or by the erosion and submergence of inactive delta lobes.

Shoals can appear as a coastal landform in the sea, where they are classified as a type of ocean bank, or as fluvial landforms in rivers, streams, and lakes.

A shoal–sandbar may seasonally separate a smaller body of water from the sea, such as:

The term bar can apply to landform features spanning a considerable range in size, from a length of a few metres in a small stream to marine depositions stretching for hundreds of kilometers along a coastline, often called barrier islands.

Composition

They are typically composed of sand, although they could be of any granular matter that the moving water has access to and is capable of shifting around (for example, soil, silt, gravel, cobble, shingle, or even boulders). The grain size of the material comprising a bar is related to the size of the waves or the strength of the currents moving the material, but the availability of material to be worked by waves and currents is also important.

Formation

Wave shoaling is the process when surface waves move towards shallow water, such as a beach, they slow down, their wave height increases and the distance between waves decreases. This behavior is called shoaling, and the waves are said to shoal. The waves may or may not build to the point where they break, depending on how large they were to begin with, and how steep the slope of the beach is. In particular, waves shoal as they pass over submerged sandbanks or reefs. This can be treacherous for boats and ships.

Shoaling can also diffract waves, so the waves change direction. For example, if waves pass over a sloping bank which is shallower at one end than the other, then the shoaling effect will result in the waves slowing more at the shallow end. Thus the wave fronts will refract, changing direction like light passing through a prism. Refraction also occurs as waves move towards a beach if the waves come in at an angle to the beach, or if the beach slopes more gradually at one end than the other.

Types

Sandbars and longshore bars

Hibokwhiteisl
White Island in Camiguin, Philippines
SandbarLongIsland1
A sandbar off Suffolk County, Long Island, New York, USA, August 2006.

Sandbars, also known as a trough bars, form where the waves are breaking, because the breaking waves set up a shoreward current with a compensating counter-current along the bottom. Sometimes this occurs seaward of a trough (marine landform).

Sand carried by the offshore moving bottom current is deposited where the current reaches the wave break.[3] Other longshore bars may lie further offshore, representing the break point of even larger waves, or the break point at low tide.

Harbour and river bars

DoomBarRiverCamelCornwall2jpg
The Doom Bar sand bank extends across the River Camel estuary in Cornwall, England, UK

A harbor or river bar is a sedimentary deposit formed at a harbor entrance or river mouth by: the deposition of freshwater sediment, or the action of waves on the sea floor or up—current beaches.

Where beaches are suitably mobile, or the river's suspended or bed loads are large enough, deposition can build up a sandbar that completely blocks a river mouth and damming the river. It can be a seasonally natural process of aquatic ecology, causing the formation of estuaries and wetlands in the lower course of the river. This situation will persist until the bar is eroded by the sea, or the dammed river develops sufficient head to break through the bar.

The formation of harbor bars can prevent access for boats and shipping, can be the result of:

In a nautical sense, a bar is a shoal, similar to a reef: a shallow formation of (usually) sand that is a navigation or grounding hazard, with a depth of water of 6 fathoms (11 metres) or less. It therefore applies to a silt accumulation that shallows the entrance to or course of a river, or creek. A bar can form a dangerous obstacle to shipping, preventing access to the river or harbour in unfavourable weather conditions or at some states of the tide.

Shoals as geological units

Mississippi River-sand bars
Shoals in the Mississippi River at Arkansas and Mississippi, USA.

In addition to longshore bars discussed above that are relatively small features of a beach, the term shoal can be applied to larger geological units that form off a coastline as part of the process of coastal erosion. These include spits and baymouth bars that form across the front of embayments and rias. A tombolo is a bar that forms an isthmus between an island or offshore rock and a mainland shore.

In places of re-entrance along a coastline (such as inlets, coves, rias, and bays), sediments carried by a longshore current will fall out where the current dissipates, forming a spit. An area of water isolated behind a large bar is called a lagoon. Over time, lagoons may silt up, becoming salt marshes.

In some cases, shoals may be precursors to beach expansion and dunes formation, providing a source of windblown sediment to augment such beach or dunes landforms.[4]

Human habitation

Since prehistoric times humans have chosen some shoals as a site of habitation. In some early cases the locations provided easy access to exploit marine resources.[5] In modern times these sites are sometimes chosen for the water amenity or view, but many such locations are prone to storm damage.[6][7]

See also

References

  1. ^ D Rutecki, E Nestler, T Dellapenna, and A Pembroke, 2014. Understanding the Habitat Value and Function of Shoal/Ridge/Trough Complexes to Fish and Fisheries on the Atlantic and Gulf of Mexico Outer Continental Shelf. Draft Literature Synthesis for the U.S. Dept. of the Interior, Bureau of Ocean Energy Management. Contract # M12PS00031. Bureau of Ocean Energy Management, U.S. Department of the Interior. 116 pp.
  2. ^ a b Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  3. ^ W. Bascom, 1980. Waves and Beaches. Anchor Press/Doubleday, Garden City, New York. 366 p
  4. ^ Mirko Ballarini, Optical Dating of Quartz from Young Deposits, IOS Press, 2006 146 pages, ISBN 1-58603-616-5
  5. ^ C.Michael Hogan (2008) Morro Creek, ed. by Andy Burnham
  6. ^ Dick Morris (2008) Fleeced
  7. ^ Jefferson Beale Browne (1912) Key West: The Old and the New, published by The Record company

External links

  • Media related to Shoals at Wikimedia Commons
  • Media related to Sandbanks at Wikimedia Commons
Clarenville

Clarenville is a town on the east coast of Newfoundland in the province of Newfoundland and Labrador, Canada. Clarenville was incorporated in 1951 and is located in the Shoal Harbour valley fronting an arm of the Atlantic Ocean called Random Sound.

The town grew in importance after it became a junction on the Newfoundland Railway where a branch line to the Bonavista Peninsula left the main line. The construction of the Trans-Canada Highway through the community in the 1960s resulted in it becoming a local service centre for central-eastern Newfoundland, serving 96,000 people living in 90 communities within a 100 km radius. Clarenville is centrally located and within two hours' driving time of 70% of the province's population.

The town is a natural gateway to the Discovery Trail, extending down the Bonavista Peninsula to Trinity and Bonavista, reputed site of the first landing of European explorer John Cabot. The trail is a panorama of scenery, historic sites, coastal towns and villages.

Iskatewizaagegan 39 Independent First Nation

Shoal Lake 39 First Nation is an Ojibwa or Anishinaabe First Nation, located along the northwestern shores of Shoal Lake, Ontario. It is officially known as Iskatewizaagegan #39 Independent First Nation. The total registered population of this First Nation is 585, of which 297 live on its own reserves. They are governed by a chief and council, with their current Chief Gerald Lewis having been elected in March 2016 for a two-year term.In April 2008, the chief of Shoal Lake 39 complained that the sewage treatment plant built for the community in 2000 had no running water to help maintain cleanliness, and that other problems with the plant could lead to a complete shut-down, resulting in raw sewage entering the lake from which Winnipeg has been drawing its drinking water for almost 100 years. In June 2009, Chief Mandamin and some community members demonstrated on the Trans-Canada Highway near their home reserve, to show their grievances with a highway-twinning project planned by the Ontario government. They also expressed frustration with the fact that the City of Winnipeg has never made an agreement with Shoal Lake 39 regarding the water that is drawn from Shoal Lake to service Winnipeg citizens, although the adjacent Shoal Lake 40 First Nation did have an agreement settled in 1989.In 2011, Iskatewizaagegan #39 First Nation voiced its concern over the plans for the City of Winnipeg to sell its water to outlying communities. That water originates in Shoal Lake, near the reserves of this First Nation, and the natives are seeking monetary compensation, or other equivalent forms of redress, for the many hardships they have endured over the years. The water taken out of Shoal Lake for the aqueduct has required artificial maintenance of lake levels, leading to loss of fishing and wild rice resources, among other difficulties arising from the loss of sovereignty over the land and water. The leaders of this #39 band have threatened to cut off the Winnipeg water supply by blocking the aquatic entrance to Shoal Lake. The neighboring Shoal Lake 40 First Nation stated that they were not willing to take such drastic measures in achieving their objectives, before negotiating with various levels of government.Iskatewizaagegan First Nation has now taken this matter of Winnipeg's water usage to the Manitoba Court of Queen's Bench. In a legal petition filed on 14 March 2012, the First Nation is asking the court to set aside a December 2011 decision by the City of Winnipeg to enter into service-sharing agreements, including one nearing completion with West St. Paul. The Shoal Lake No. 39 band also wants the court to order the city to refrain from any more negotiations until it reaches an agreement with the First Nation on how the water may be used. This First Nation has long maintained Winnipeg did not obtain its consent as far back as 1919, although a neighbouring band, Shoal Lake No. 40, has no such dispute with the city.Four Reserves are attached to this First Nation. They are:

Agency 30, shared with 12 other First Nations

Shoal Lake 34B2, shared with Shoal Lake 40 First Nation

Shoal Lake 39, partly located in Manitoba adjacent to the north of Shoal Lake

Shoal Lake 39A, northwest of Lake of the Woods

James Shoal

James Shoal, also called Beting Serupai in Malaysia and Zengmu Reef (Chinese: 曾母暗沙; pinyin: Zēngmǔ Ànshā) in Greater China, is a small bank in the South China Sea, with a depth of 22 metres (72 ft), located about 45 nautical miles (83 km; 52 mi) off the Borneo coast of Malaysia. It is claimed by Malaysia, the People's Republic of China, and the Republic of China (Taiwan). The shoal and its surrounds are administered by Malaysia.

Lisianski Island

Lisianski Island (Hawaiian: Papa‘āpoho) is one of the Northwestern Hawaiian Islands, with a land area of 384.425 acres (155.571 ha) and a maximum elevation of 40 feet (12 m) above sea level. It is a low, flat sand and coral island about 905 nautical miles (1,676 km) northwest of Honolulu. The island is surrounded by reefs and shoals, including the extensive Neva Shoals. Access to the island is limited by helicopter or by boat to a narrow sandy inlet on the southeastern side of the island.

Municipality of Shoal Lake

The Municipality of Shoal Lake is a former rural municipality (RM) in the Canadian province of Manitoba. It was originally incorporated as a rural municipality on January 1, 2011. It ceased on January 1, 2015 as a result of its provincially mandated amalgamation with the RM of Strathclair to form the Rural Municipality of Yellowhead.The former Municipality of Shoal Lake is located in the Westman Region of the province. Its formation on January 1, 2011 was a result of an amalgamation of the former Town of Shoal Lake and the former Rural Municipality of Shoal Lake. It had a population of 555 according to the Canada 2006 Census.

North Shoal Creek, Austin, Texas

North Shoal Creek is a neighborhood in north central Austin, Texas established in the 1960s.

North Shoal Creek comprises United States Census tract 18.17 and ZIP code 78757 in Travis County. The area is bordered by Mopac to the west, Research Blvd on the North, Burnet Road to the East and Anderson Lane on the South, located in the north part of the City of Austin's Urban Core and increasingly popular North Burnet Road Area. The North Shoal Creek neighborhood borders the following neighborhoods: Allandale (to the south), Wooten (to the east), North Burnet (to the north) and Northwest Hills (to the west).

Centrally located in between Mopac Expressway/Loop 1 (to the west) and 183/Research Blvd. (to the north), the North Shoal Creek neighborhood has an area of 1.179 square miles (3.1 km2) and a population of 4,302 or 0.6% of Austin's population.The neighborhood area is pedestrian friendly and integrates bus routes, biking trails and sidewalks. It is located next to retail and recreational facilities, many of which are local businesses, businesses include: The Village Alamo Drafthouse, Fresh Plus, Chipotle, Hopdoddy Burger Bar, Chen Z, Tarka, The Goodnight and other newly opened restaurants and local shops. The main thoroughfare of West Anderson Lane has seen tremendous redevelopment since 2005 with the opening of Cover 3, Office Depot, Wal-Mart, and other shops.

According to the website Walk Score, North Shoal Creek is the 14th most walkable neighborhood in Austin; the neighborhood scores Very Walkable with an average Walk Score of 74, scoring 21 points higher than Austin's overall Walk Score of 49.

Nowra, New South Wales

Nowra is a town in the South Coast region of New South Wales, Australia. It is located 160 kilometres (99 mi) south-southwest of the state capital of Sydney (about 120 kilometres (75 mi) as the crow flies.) With its twin-town of Bomaderry, as at the 2016 census, Nowra had an estimated population of 35,795. It is also the seat and commercial centre of the City of Shoalhaven. Geologically, the city is situated in the southern reaches of the Sydney basin.The region around Nowra is a farming community, sustaining a thriving dairy industry and a number of State forests, but is also increasingly a retirement and leisure area for Canberra and Sydney. The naval air station HMAS Albatross is located about 10 kilometres (6.2 mi) south-west of Nowra. The name Nowra, originally written by Europeans as 'nou-woo-ro' (pronounced Nowa Nowa by the Indigenous Australians of the area), is an Aboriginal word for black cockatoo.

Reefs Harbour-Shoal Cove West-New Ferolle

Reefs Harbour-Shoal Cove West-New Ferolle is a designated place in the Canadian province of Newfoundland and Labrador, located southwest of Anchor Point. The area consists of three unincorporated communities, Reefs Harbour, Shoal Cove and New Ferolle, located on the New Ferolle Peninsula near Port au Choix.

The area had a population of 230 in the Canada 2011 Census.

Scarborough Shoal

Scarborough Shoal, also known as Huangyan Dao (Filipino: Kulumpol ng Panatag),, Bajo de Masinloc (Spanish),, and Democracy Reef are two rocks in a shoal located between the Macclesfield Bank and Luzon island in the West Philippine Sea.

It is a disputed territory claimed by the People's Republic of China, the Republic of China (Taiwan) and the Philippines. The shoal's status is often discussed in conjunction with other territorial disputes in the South China Sea such as those involving the Spratly Islands, and the 2012 Scarborough Shoal standoff. It formerly was administered by the Philippines, however, due to the 2012 Scarborough Shoal standoff, where China sent warships to invade the shoal, the administration of the shoal was taken by the People's Republic of China. It was initially expected for the United States to defend the territory of the Philippines during the standoff as the two nations had a Mutual Defense Treaty, however, the United States chose to move itself away from the tension, and used 'verbal protests' against China instead. The aftermath of the standoff ultimately strained Philippines-China relations and Philippines-United States relations, resulting in Filipino officials calling the United States an 'unreliable ally', a statement echoed by other nations. The event also solidified China's expansionist ideals in the Asia-Pacific region. In 2013, the Philippines solely filed an international case against China in the UN-backed court in The Hague, Netherlands. In 2016, the court officially dismissed China's so-called "9-dash claim" in the entire South China Sea and upheld the Philippine claim. China rejected the UN-backed international court's decision and sent more warships in Scarborough Shoal and other islands controlled by China.The shoal was named by Captain Philip D'Auvergne, whose East India Company East Indiaman Scarborough grounded on one of the rocks on 12 September 1784, before sailing on to China.

Scarborough Shoal standoff

The Scarborough Shoal standoff refers to tensions between China (PRC) and the Philippines which began on April 8, 2012 over the Philippine Navy apprehension of eight mainland Chinese fishing vessels in the disputed Scarborough Shoal.

Shoal Lake 37A

Shoal Lake 37A is a First Nations reserve on Shoal Lake straddling the border between Manitoba and Ontario. It is one of the reserves of the Animakee Wa Zhing 37 First Nation.

Shoal Lake 39

Shoal Lake 39 is a First Nations reserve on Shoal Lake straddling the border between Manitoba and Ontario. It is one of the reserves of the Iskatewizaagegan 39 Independent First Nation.

Shoal Lake 39A

Shoal Lake 39A is a First Nations reserve straddling the border of Manitoba and Ontario on the shores of Shoal Lake. It is one the reserves of the Iskatewizaagegan 39 Independent First Nation.

Shoal Lake 40

Shoal Lake 40 is a First Nations reserve straddling the border of Manitoba and Ontario on the shores of Shoal Lake. It is one the reserves of the Shoal Lake 40 First Nation.

Shoal Lake 40 First Nation

Shoal Lake 40 First Nation is an Ojibway or Ontario Saulteaux First Nation reserve located in the Eastman Region of Manitoba and the Kenora District of Ontario. The total registered population in September 2017 was 641, of which the on-reserve population was 285. The First Nation is a member of the Bimose Tribal Council, a Regional Chief's Council that is a member of the Grand Council of Treaty 3.

This First Nation's community inhabits a man-made island. It is accessible via barge traffic from Iskatewizaagegan 39 First Nation's dock, located in the community of Kejick, Ontario, and in winter by ice roads. The construction of a new all-season road to link this community with the Trans-Canada Highway is now more certain, after an agreement was reached between three levels of government, on how the cost would be covered.The First Nation possess basic infrastructure, limited retail outlets, indoor and outdoor recreational facilities and provide local elementary schooling to Grade 8.

Shoal Lake Cree Nation

The Shoal Lake Cree Nation is a Swampy Cree First Nations band government in Saskatchewan, Canada located 98 kilometres (61 mi) east of Nipawin. The Cree First Nation is on the Carrot River and can be accessed by Highway 55. Nearby to the west is the Red Earth First Nation.

Shoaling and schooling

In biology, any group of fish that stay together for social reasons are shoaling (pronounced /ˈʃoʊlɪŋ/), and if the group is swimming in the same direction in a coordinated manner, they are schooling (pronounced /ˈskuːlɪŋ/). In common usage, the terms are sometimes used rather loosely. About one quarter of fish species shoal all their lives, and about one half shoal for part of their lives.Fish derive many benefits from shoaling behaviour including defence against predators (through better predator detection and by diluting the chance of individual capture), enhanced foraging success, and higher success in finding a mate. It is also likely that fish benefit from shoal membership through increased hydrodynamic efficiency.

Fish use many traits to choose shoalmates. Generally they prefer larger shoals, shoalmates of their own species, shoalmates similar in size and appearance to themselves, healthy fish, and kin (when recognized).

The "oddity effect" posits that any shoal member that stands out in appearance will be preferentially targeted by predators. This may explain why fish prefer to shoal with individuals that resemble themselves. The oddity effect thus tends to homogenize shoals.

Thomas Point Shoal Light

The Thomas Point Shoal Light, also known as Thomas Point Shoal Light Station, is a historic lighthouse in the Chesapeake Bay on the east coast of the United States, and the most recognized lighthouse in Maryland. It is the only screw-pile lighthouse in the bay which stands at its original site. The current structure is a 1½ story hexagonal wooden cottage, equipped with a foghorn as well as the light.

West Sixth Street Bridge

The West Sixth Street Bridge is a historic stone arch bridge in downtown Austin, Texas. Built in 1887, the bridge is one of the state's oldest masonry arch bridges. It is located at the site of the first bridge in Austin, carrying Sixth Street across Shoal Creek to link the western and central parts of the old city. The bridge was added to the National Register of Historic Places in 2014.

Landforms
Beaches
Processes
Management
Related

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.