Much of the Boston that we see today stems from the building of the Grand Sluice on the River Witham. It was built to enable easy and reliable navigation between Boston and Lincoln and to help with the drainage of large areas of fen. This heralded a new era of prosperity for Boston and many of the fine buildings we have today date back to this time. It also enabled the town to become the first in Lincolnshire to be industrialised and grow to be the largest in the County.
The River Witham rises near the village of South Witham close to the border with Rutland then flows through Grantham, before reaching Lincoln. After passing through Lincoln’s Brayford Pool and under the city’s High Bridge, it continues its way to the sea. Lincoln’s High Bridge was built in 1160 and is the oldest bridge in the UK with a building on it.
After Lincoln, the river passes Bardney and Kirkstead, sites of important medieval monasteries, before flowing towards Boston and through the Grand Sluice. From there it passes Boston’s famous Stump and through Boston’s Haven finally reaching the Wash. The total length of the river is 82 miles (132km). The important section from Lincoln High Bridge to the Grand Sluice is 31 miles long, with the fall in water level usually only about 4.5m. Before the Grand Sluice was built commercial navigation between Lincoln and Boston had become all but impossible as the Witham meandered, silted up and even changed its course from time to time.
Construction of the Grand Sluice began in 1764 and whilst this work was being carried out the Witham was straightened out and confined between the high banks we see today. Work on the Sluice began in the middle of a field and a totally new course for the Witham was cut ready for the opening in 1766. The Sluice consists of three channels each 5.2 m wide fitted with mitre gates on both sides. Three engineers were involved: John Grundy, Langley Edwards and John Smeaton. Edwards designed the actual Sluice and was appointed as project engineer.
The Sluice controls the water levels for the 21 miles upstream to Bardney Lock. Its construction and the accompanying river improvement enabled 111,000 acres of land in the Holland, Wildmore, East and West Fens and the Lincoln Fens to be drained; then enclosed into fields for growing crops. As a result, large quantities of grain and other produce were grown, shipped to London or the new industrialised areas of the North.