57: Denver Sluice
In a region where the balance between land and water has been measured in inches, Denver Sluice in West Norfolk helps maintain the equilibrium.
A vital role, particularly today.
Denver Sluice is a complex array of mechanisms for managing water levels as far away as Essex. In modern Britain water is a ‘hot’ topic, and we worry over the effect of rising sea levels as well as, conversely, the impact of lack of rain during the summer. In the fenland area water has always been an issue; Denver Sluice has been at the centre of this man-made environment since it was first dug by a Dutch engineer of great genius in 1651, surviving natural and manmade disasters, the impact of shrinking land and changing river courses.
And became a popular spot with the boating fraternity.
Denver Sluice: a complex system for managing water levels.
Denver is two miles from Downham Market, and the sluice stands on the River Ouse, next to the Jennyns Arms pub and Denver Sailing Club. Linking the Norfolk Broads to the waterways of the East Midlands, it is a busy place. But leisure was not its original purpose. When the great landowners of the 17th century sought to drain the vast wetlands of the fens to create the fertile farmland we see today they faced many problems. Apart from the vast scale of the project, which involved digging out channels to straighten the course of the meandering rivers, they also incurred hostility from the local people – the Fen Tigers. They carried on guerilla resistance for many years, attacking the navigators, breaking the sluices and sabotaging the works. It was the Dutch engineer, Cornelius Vermuyden, who orchestrated most of the work. The problems were eventually overcome; during a tortuous period of 20 years, interrupted by the Civil War, the work was completed. The principal engineering achievement of the operation was the construction of the major channels the Old Bedford River and the Forty Foot and Hundred Foot Rivers (known as Drains).
Where did Denver Sluice fit in?
Below Denver, the Ely Ouse waters converged for the journey to the sea. Tidal water from The Wash created a risk of flooding the newly-drained lands. To counter this, the first Denver Sluice was built in 1651 across the Ely Ouse at the lower end of the Hundred Foot River. This shut out the tidal water from the South Level rivers and turned it up the Hundred Foot. It meant the water could be controlled all year round.
So that was that then...
Merely the beginning. Vermuyden had solved the problem of containing the vast volume of water south of Denver, in what was known as the Middle Level, but not in the region towards The Wash. When the sluice was open, the Ouse could flow to the sea. But water levels in the Hundred Foot were often higher than in the Ouse – consequently the sluice doors were often shut. This slowed the river, and led to siltation. Traffic was reduced and prices rose, so not everyone was happy with the Denver Sluice. Other results of fen drainage were unforeseen in the 17th century. Soon the dried-out peat land was shrinking at an alarming rate. A strange, upside down, landscape emerged within a few decades, with the new waterways actually standing above the level of the land around them. Just digging higher embankments made little difference. Soft “buttery clay” soil added to shrinking peat created unstable flood defences liable to saturation.
A disaster waiting to happen?
As early as 1695 that indefatigable traveller Celia Fiennes, while on her marathon horseback tour of England, wrote that she was forced to ride along raised river banks as the land around was flooded. The capture of an oceanborne 7ft 8in long sturgeon at Thetford merely demonstrated that the sea was breaking through. In 1713 exceptionally high tides led to severe flooding and Denver Sluice was wrecked. Within seven years the Hundred Foot flooded. Instead of taking its natural course to the sea, the water followed the new fall of the Ely Ouse and turned inland towards Cambridge. Land in the South Level was drowned, and many farmers were ruined. Something had to be done. Vermuyden’s great work of the previous century was in peril.
What was the solution?
Swiss engineer Labelye eventually rebuilt the sluice in 1750, along with a lock that enabled larger vessels to navigate water at different levels. Even then it was not universally popular with those who claimed it slowed river trade. The current sluice dates from 1834, when Sir John Rennie constructed three main sluice gates and again widened the lock. In the surrounding area steam-powered pumps were introduced in the early 19th century, which helped get rid of excess water. Twentieth century technology provided diesel and electric pumping. Yet the risk remained high. In 1947 the worst flood in recorded history swamped the fens, covering 40,000 acres. It was as serious a situation as in the 1700s, yet the answer turned out to have been provided way back in 1642.
That Dutchman again?
In 1949, Sir Murdoch MacDonald’s Flood Protection Scheme was approved by Parliament. At a cost of £10.5m over more than 10 years it actually mirrored an original drawn up at the start of the Civil War by that clever Mr Vermuyden, which he never got to carry out. A relief channel was dug parallel with the tidal Ouse from Denver to Saddlebow. It provided a second route for water to be sent quickly to the sea from Denver. The Ouse was widened and deepened to improve flow and connected to the new relief channel by a sluice. After 300 years the old problem of moving surplus water from the fens to the sea was solved on completion of the scheme in 1964. But what of the future? If sea levels rise as pessimistic experts claim they will, the water would reclaim its own – and Denver Sluice would be consigned to history.
Denver Sluice, managed by the Environment Agency, is near Downham Market.
Website: /www.environment-agency.gov.uk/
