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Tide mill

Tide mill

A tide mill is a specialist type of water mill driven by tidal rise and fall.

A dam with a sluice is created across a suitable tidal inlet, or a section of river estuary is made into a reservoir. As the tide comes in, it enters the mill pond through a one way gate, and this gate closes automatically when the tide begins to fall. When the tide is low enough, the stored water can be released to turn a water wheel.

Tide mills are usually situated in river estuaries, away from the effects of waves but close enough to the sea to have a reasonable tidal range. These mills have existed since the Middle Ages, and some may go back to the Roman period.

Early history

Possibly the earliest tide mill was located in London on the River Fleet, dating back to Roman times. The earliest excavated tide mill, dating from 787, is the Nendrum Monastery mill on an island in Strangford Lough in Northern Ireland. Its millstones are 830mm in diameter and the horizontal wheel is estimated to have developed 7/8HP at its peak. Remains of an earlier mill dated at 619 were also found.

The earliest recorded tide mill in England was in Dover harbour, mentioned in the Domesday book (1086), as were the mills on the Lea River at Three Mills Island, now in London's docklands, which by the 18th Century had become the largest in England. There were many tide mills in London, including two on London Bridge.

Woodbridge Tide Mill, an excellent example, survives at Woodbridge, Suffolk, England. This mill, dating from 1170 and reconstructed in 1792, has been preserved and is open to the public. Its water wheel can be seen turning. The only working tide mill in the United Kingdom is Eling Tide Mill in Eling, Hampshire. Another example, now only visible in historic documents, is the mill in the hamlet of Tide Mills, East Sussex.

A mediaeval tidemill still operates at Rupelmonde near Antwerp, and there are several still in existence in the Netherlands.

At one time there were 750 tide mills operating along the shores of the Atlantic Ocean. Approximately 300 in North America, 200 in the British Isles, and 100 in France. The Rance estuary in France was also home to some of these mills.

Modern examples

Newer types of tidal power often propose a dam across a large river estuary. Although it represents a source of renewable energy, each proposal tends to come under local opposition because of its likely impact on coastal habitats. One proposal, which came to fruition in 1966, is the Rance barrage which generates 250MW. Unlike historical tide mills which could only operate on an ebb tide, the Rance barrage can generate electricity on both flows of the tide or it can be used for pumped storage depending on demand. A less intrusive design is for a 1MW free standing turbine, being constructed at Strangford Lough Narrows - also close to an old tide mill.

See also

References

Further reading

  • McErlean, T. & Crothers, N.: “Harnessing the Tides: The Early Medieval Tide Mills at Nendrum Monastery, Strangford Lough”, 2007, The Stationery Office, UK, ISBN 0337088772
  • Minchinton, W. E. : "Early Tide Mills: Some Problems", Technology and Culture, Vol. 20, No. 4 (Oct. 1979), pp. 777-786
  • Rynne, Colin: "Milling in the 7th Century – Europe’s earliest tide mills", in: Archaeology Ireland 6, 1992
  • Spain, Rob: "A possible Roman Tide Mill", Paper submitted to the Kent Archaeological Society

External links

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