The Outer Trial Bank is a circular artificial island

Artificial island

An artificial island or man-made island is an island or archipelago that has been constructed by people rather than formed by natural means...

 in the Wash

The Wash

The Wash is the square-mouthed bay and estuary on the northwest margin of East Anglia on the east coast of England, where Norfolk meets Lincolnshire. It is among the largest estuaries in the United Kingdom...

, East Anglia

East Anglia

East Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. It is one of two islands constructed during the 1970s for a governmental water resources

Water resources

Water resources are sources of water that are useful or potentially useful. Uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water....

 scheme.

Background

In 1972, the Government

Government of the United Kingdom

Her Majesty's Government is the central government of the United Kingdom of Great Britain and Northern Ireland. The Government is led by the Prime Minister, who selects all the remaining Ministers...

 undertook a study to assess the feasibility of building a tidal barrage

Barrage (tidal)

A barrage is an artificial obstruction at the mouth of a tidal watercourse.-Purpose:The common primary functions of a barrage are:* Increase the depth of a river * Maintain a separation between fresh and salt water...

 across half of the Wash. The idea was to capture the freshwater from the River Witham

River Witham

The River Witham is a river, almost entirely in the county of Lincolnshire, in the east of England. It rises south of Grantham close to South Witham, at SK8818, passes Lincoln at SK9771 and at Boston, TF3244, flows into The Haven, a tidal arm of The Wash, near RSPB Frampton Marsh...

, River Welland

River Welland

The River Welland is a river in the east of England, some long. It rises in the Hothorpe Hills, at Sibbertoft in Northamptonshire, then flows generally northeast to Market Harborough, Stamford and Spalding, to reach The Wash near Fosdyke. For much of its length it forms the county boundary between...

, River Nene

River Nene

The River Nene is a river in the east of England that rises from three sources in the county of Northamptonshire. The tidal river forms the border between Cambridgeshire and Norfolk for about . It is the tenth longest river in the United Kingdom, and is navigable for from Northampton to The...

 and Great Ouse to build a freshwater reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

. The study also intended to establish potential improvements to the navigation of sea locks, provide recreational facilities and develop an area of land for a power station.

Construction of the banks

As part of the test, the approval to build an artificial island 2 miles (3.2 km) off the Lincolnshire

Lincolnshire

Lincolnshire is a county in the east of England. It borders Norfolk to the south east, Cambridgeshire to the south, Rutland to the south west, Leicestershire and Nottinghamshire to the west, South Yorkshire to the north west, and the East Riding of Yorkshire to the north. It also borders...

 coast was given in November 1974. Building work began in February 1975. The bank (known locally as "the doughnut" due to its biconcave shape) was constructed of a sand fill protected by limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 riprap

Riprap

Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...

. Measuring 250 metres (820.2 ft) in diameter, the island contained a small reservoir measuring 1 hectares (2.5 acre) in the centre.

The other trial bank, built before the Outer Trial Bank, is connected to Norfolk

Norfolk

Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...

 by a causeway

Causeway

In modern usage, a causeway is a road or railway elevated, usually across a broad body of water or wetland.- Etymology :When first used, the word appeared in a form such as “causey way” making clear its derivation from the earlier form “causey”. This word seems to have come from the same source by...

 on Terrington Marsh.

Conclusions

The study, which was published in 1976 as "The Wash storage scheme", found that the trial alone proved financially unfeasible (costing £3 million), and that the freshwater was too close to the tidal estuary to ensure low salinity and minimal silt levels. The trial was soon abandoned and the plans for the scheme shelved.

Present use

The outer bank is now used as a nesting ground for seabird

Seabird

Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...

s within the National Nature Reserve

National Nature Reserves in England

National Nature Reserves in England are managed by Natural England and are key places for wildlife and natural features in England. They were established to protect the most important areas of habitat and of geological formations...

of the Wash. In 2008, an estimated 3,000 pairs of birds nested on the island.