The River Lymn is a river in Lincolnshire, England. It rises in the Wolds on the eastern slope of Castcliffe Hill in Fulletby parish. It flows south-eastwards to the Lincolnshire Marsh, where it becomes known as the Steeping River on the boundary of Great Steeping parish. The main channel is supplemented by the Wainfleet Relief Channel as it passes Wainfleet All Saints, and the relief channel is joined by the old course of the Lymn. Once the two channels rejoin, there are three flood defence structures to protect the region from flooding by the North Sea. The river flows into the North Sea at Gibraltar Point.
Route
The river rises on the southern slope of Belchford Hill, to the east of Belchford and close to the contour. It flows to the south and then to the east to reach Tetford, where there is a grade II listed water mill and mill house. It was built in the late eighteenth century, but shows evidence that it was built around an earlier structure. The much-repaired water wheel, dating from the seventeenth century, and the corn milling machinery are still intact. Beyond Tetford the river is joined by Double Dike, and flows south through woodland, passing to the west of Somersby and Bag Enderby. Here it is joined by a second stream, which rises on the eastern slope of Castcliffe Hill in Fulletby, close to the contour. It flows through a large lake and is joined by a stream from Holbeck Manor before passing through Salmonby. By the time the two streams join, they are below the contour. Warth's Bridge and Thorpe Culvert Bridge follow, both roads leading to Thorpe Culvert railway station. Thorpe Culvert pumping station, owned by the IDB, is located just before the second bridge, and after it, the Wainfleet Relief Channel turns off, passing under the railway almost immediately. There are two more bridges as the main channel crosses Wainfleet Common, Bycroft's Bridge and Crow's Bridge. Salem Bridge carries the B1195 road to Wainfleet railway station, and the A52 road crosses to the east of Wainfleet All Saints. The channel is now also called Wainfleet Haven, and both names are used to describe it until it reaches the sea. Croft Lane bridge is next, after which the A52 and the Boston to Skegness railway cross, and the relief channel rejoins Wainfleet Haven. The final section contains three flood defence structures. Haven House Sluice is first, after which the channel splits. Wainfleet Clough Outfall is on the western channel, which is tidal below the sluice. The Burgh Sluice Relief Channel is to the east, and Burgh Sluice protects it from the sea just before the two channels rejoin. Gibraltar Point Sailing Club is located at Gibraltar Point, and the east bank of the river channel is used for mooring yachts. As the layers of rock continue to dip to the east, they are covered by boulder clay, gravel and alluvium.
Flow on the upper river is measured by a gauging station at Partney Mill, consisting of a Crump weir with a crest. The catchment area of the river above this point is , and this area received annual rainfall of in the 1960s. This produces an average daily flow of 9.5 million gallons (43.2 Megalitres (Ml)), although a peak flow of 253M gallons (1149 Ml) was recorded in April 1981.
Discharge to the North Sea is along the Burgh Sluice Relief Channel during the winter and at times of high flow, but when flows in the river are low, Wainfleet Clough Sluice is used as the discharge point.
The Environment Agency measure water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail.
The water quality of the Lymn and Steeping was as follows in 2019.
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Like most rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE) and mercury compounds, neither of which had previously been included in the assessment.
History
thumb|right|Haven House Sluice on the lower Wainfleet Haven or Steeping River
The manipulation of the river channel has a long history, dating back to at least the thirteenth century, when the river was diverted to the south at Firsby Clough and then to the east at White Cross Clough, creating two channels. Because the old channel ran through the manor of Croft, and was used to supply drinking water for cattle, an agreement for its management was reached in 1240. The flow was diverted along the old channel for the first three weeks after Easter, and then along the new channel for three weeks. This six-week cycle was repeated until Michaelmas (29 September). The arrangement was ratified by the Court of Sewers in 1432 and 1501, and continued in operation until at least 1774. The original channel is the Lymn, while the southern channel has been straightened and enlarged to become the Steeping River.
Thorpe Culvert takes its name from a culvert which was built under the river to drain water into the Bell Water Drain. The area to the north of the culvert became part of the Witham Fourth District in 1818, and the culvert was built soon afterwards. Responsibility for the drain passed to the Witham and Steeping Catchment Board following the passing of the Land Drainage Act in 1930, and they commissioned a new pumping station to pump water from the drain into the Steeping in 1938.
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