The South Forty-Foot Drain, also known as the Black Sluice Navigation, is the main channel for the land-drainage of the Black Sluice Level in the Lincolnshire Fens. It lies in eastern England between Guthram Gowt and the Black Sluice pumping station on The Haven, at Boston. The Drain has its origins in the 1630s, when the first scheme to make the Fen land available for agriculture was carried out by the Earl of Lindsey, and has been steadily improved since then. Water drained from the land entered The Haven by gravity at certain states of the tide until 1946, when the Black Sluice pumping station was commissioned.

The Drain was navigable until 1971, when improvements to the pumping station led to the entrance lock being removed. It is currently being upgraded to navigable status by the Environment Agency, as part of the Fens Waterways Link, with a new entrance lock being completed in December 2008, giving access to the first of the drain, and the upgrading of the southern section, including a link to the River Glen to allow navigation to Spalding forming phase 2 of the project.

History The Lincolnshire Fens are an area of low-lying land which have been subject to flooding and attempts to prevent it for centuries. In medieval times, the Midfen Dyke was built to drain the area, but by 1500, this was regarded less as a drain for the land than as a boundary marker between the Parts of Holland and the Parts of Kesteven, two of the three medieval subdivisions of Lincolnshire which functioned as county councils until their abolition in 1974. The first serious attempt to drain the area to the south west of Boston, now known as the Black Sluice Area but formerly known as the Lindsey Level, was from 1635 to 1638, when the Earl of Lindsey agreed with the Commissioners of Sewers for Lincolnshire to carry out drainage works which would make of land available for agricultural use. The Earl and a group of Adventurers paid for the works, in return for land grants.

The cost of the work was £45,000, and involved the construction of a sluice near Boston, called Skirbeck Sluice, the construction of the first of the South Forty-Foot Drain, from Boston to Great Hale, the construction of two drains from there to Guthram, which were called the Double Twelves, and the construction of the Clay Dyke Drain. The scheme was not popular with the local fenmen, who made a living from fishing and wildfowling, or with the Commoners, who had a right to graze animals on the common land when it was not flooded. They attempted to get Parliament to rule in their favour, but after three years of trying, they abandoned the idea of legal redress, and took direct action. They destroyed much of the work, as well as buildings and crops, and burnt Skirbeck Sluice. The Earl of Lindsey's contract with the Commissioners of Sewers was revoked by parliament, and it was another hundred years before the next attempt to drain the area.

In an attempt to drain Holland Fen, and prevent flooding from the River Witham, an adventurer called Earl Fitzwilliam constructed a drain in 1720, which runs broadly parallel to the River Witham, and terminated at Lodewick's Gowt, a sluice which he constructed on the Witham close to the location of the present Grand Sluice. The drain was for many years called Earl Fitzwilliam's drain, but is now called the North Forty-Foot Drain. The scheme was not entirely successful.

Second Sluice

The Witham Drainage Act 1762 (2 Geo. 3. c. 32) among other things constituted the Commissioners of Sewers for the Second and Sixth District, which covered the area including Asgarby, Ewerby, Great Hale, Heckington, Holland Fen, Howell, Little Hale and South Kyme. Much of the area to the south and west of Boston, some , was inundated by the Great Flood of 1763, and against this background, the (5 Geo. 3. c. 86 ) was obtained which created the Black Sluice Commissioners, giving them power to raise taxes and authority to carry out drainage works. The scheme largely revived the Earl of Lindsey's original scheme. The initial design work was carried out by the civil engineer Langley Edwards, on loan from the Witham Commissioners. Some of the surveying was performed by John Landen, who was the steward of the estate of Earl Fitzwilliam at Peterborough, and a proficient amateur mathematician. The two men were jointly appointed Surveyors of the Works, acting as engineers for the scheme, while John Chapman and Richard Strattard were assistants. A new sluice, called the Black Sluice, was built at Boston as a direct replacement for the Skirbeck Sluice, having three openings with a total width of . The of the drain were scoured from Boston to Great Hale, beyond which the Main Drain was upgraded by cutting a new channel, effectively extending the South Forty-Foot Drain to Guthram, on the banks of the River Glen. A total of of highland streams were improved by scouring and raising of the banks. The estimated cost of £16,000 was raised by issuing bonds, but the project overran, and another act of Parliament, the (10 Geo. 3. c. 41 ) was obtained in 1770 to authorise the raising of the drainage taxes, to cover the difference. By mid-1769, when Landen and Edwards left the project, because the work was largely complete, the scheme had cost £24,000. They were replaced by Edward Hare as Surveyor of Works, with Chapman and Strattard continuing as assistants. A historian called W. H. Wheeler, who chronicled the Lincolnshire fens, wrote that "the works were efficiently carried out and, being well-designed, entirely answered expectation."

On the River Witham, the Grand Sluice was constructed and opened on 15 October 1766, and this prevented tidal water from entering the river, and hence flooding the Holland Fen. The Boston Harbour Commissioners were created by the Boston Port Act 1766, and they carried out improvement works to The Haven, which resulted in lower water levels at the Black Sluice, and hence more efficient draining from the South Forty-Foot Drain. Water was pumped into the drain by a series of windmills driving scoop wheels. Maps of the area produced in 1783 by Edward Hare show 46 such mills, which provided drainage for of agricultural land. Extreme high tides in 1810 and again in 1820 resulted in widespread flooding, and further thought was given to improving the flood defences.

With the improvements to the River Witham, the final section of Earl Fitzwilliam's drain to Lodewick Gowt was filled in, and the channel was diverted to join the South Forty-Foot Drain. Renamed the North Forty-Foot Drain, it now supplies Cook's Lock and Holland Fen pumping stations.

Third Sluice Reports on improvements to the system were produced in 1843 by the surveyor Mr W Lewin and in 1845 by Sir John Rennie. Rennie's scheme involved the provision of a catchwater drain to collect water draining from the higher ground to the west before it entered the fenlands, but an Act of Parliament to authorise its construction was defeated, and so in 1846 a report by Mr W Cubit which proposed improvements to the existing infrastructure was accepted by the Commissioners. A new Black Sluice, including a wide navigation lock, was constructed to the south of the original one, with the cill level lower, which enabled the gradient of the South Forty-Foot Drain to be increased to 3 inches per mile (5 cm/km). Many of the tributary drains were also improved. 1846 also marked the beginning of the use of steam engines for pumping. Ten years later, a map covering of the Black Sluice area showed nine steam-powered and eight wind-powered drainage engines in use.

The River Witham Outfall Improvement Act 1880 (43 & 44 Vict. c. cliii) authorised further improvements to the mouth of the Witham, to which the Black Sluice Commissioners contributed £65,000. This work led to a further drop of in the low water level at the Black Sluice. Oil and paraffin engines began to replace steam and wind engines from 1910, and by 1935 there were 15 such engines pumping water into the South Forty-Foot Drain. The passing of the Land Drainage Act 1930 resulted in the Commissioners being replaced by the Black Sluice Internal Drainage Board, while responsibility for the rivers in the area passed to the Witham and Steeping Rivers Catchment Board. With war imminent, the Rivers Board took over the Black Sluice and the South Forty-Foot Drain in 1939, and although progress was interrupted by the Second World War, a £374,000 scheme to construct the Black Sluice pumping station and to widen of the drain from Boston to Donington Bridge was completed in 1946. The pumping station contained three pumps, each powered by a 5-cylinder vertical diesel engine manufactured by Ruston.

Modern era Paraffin and oil engines gave way to electrically powered pumping stations in the 1950s, with the Board constructing six electric and one diesel pumping station to improve drainage to an extra of land. In 1960, the decision was taken to further improve drainage of an area of , as part of a £1.4 million scheme which included the addition of two extra pumps at the Black Sluice, replacement of existing pumps elsewhere, and the widening of of the South Forty-Foot Drain from Donington Bridge to Rippingale Running Dyke. Jurisdiction for the Drain and the sluice passed to the Lincolnshire River Board at this time. The work, which began in 1962 and was completed in 1968, proved successful in preventing flooding during severe wet weather in the winter of 1968/9. With three and two diesel engines, the upgraded pumping station could pump 800,000 gallons per minute (60 m3/s). Responsibility for the drain and the sluice passed to the National Rivers Authority in 1990, and to the Environment Agency in 1995.

Despite all the improvements, serious flooding occurred in 1999 when the bank of the drain was breached near Pinchbeck. Staff from the Environment Agency and the Black Sluice Internal Drainage Board successfully repaired the breach before properties were flooded, and a review of the flood defences was then carried out. The report recommended improvements to some of the banks, but funding for the work was not available, and so no work was done at the time.

In 2013, the pumping station flooded as a result of a tidal surge. The three engines dating from 1946 were damaged by water ingress, and were decommissioned. The other two engines were at a higher level, and remained operational, but were by that time nearly 50 years old, and nearing the end of their operational life. Refurbishment of the pumping station was estimated to cost between £15 and £20 million, and so the effectiveness of the station was reviewed. The review showed that it had been used for less than 2 days of every 100 days since it was constructed in 1946, and that the station barely affected the number of properties that might be flooded. By using the adjacent gravity sluice and the lock to discharge water from the South Forty-Foot Drain, better control of water levels could be achieved, and this had been demonstrated during a period of heavy rainfall in spring 2018. Accordingly, the remaining two pumps were decommissioned in October 2018, and the Environment Agency began looking at what to do with the building.

Functions

The South Forty-Foot Drain serves as a district boundary over the length where it runs roughly south to north. South of Donington High Bridge, the Drain separates South Kesteven to the west from South Holland to the east. The boundary then continues southwards along the River Glen. North of Donington, the boundary between the borough of Boston to the east and North Kesteven to the west follows the line of the Drain. As the Drain crosses the line of the Midfen Dyke, just before the Nottingham to Boston railway joins it at Great Hale pumping station, the boundary turns northwards, following its medieval course.