If you are regularly driving down the A10 between Ely and King’s Lynn, you may well have noticed, between Hilgay and Denver, a large sign next to a stream notifying that you are crossing the Cut Off Channel.
Have you ever wondered, like me, what’s the story of this relatively wide piece of water? Well, search no more, because here we will be lifting some of the mysteries.
Sign along A10, just north of Hilgay, when crossing the Cut Off Channel. Source: Google maps.
In fact, the below information has been kindly supplied by Chris Holley, a Stretham-based local historian, who for many years has been researching engineering and other fascinating features in the Fen landscape. A few years back he wrote a substantial report just about the Cut Off Channel, from which the below information has been obtained. He provided me with a copy earlier this year, which has helped me to understand the history and functions of this intriguing canal.
Aftermath of the 1947 floods
A detailed study of drainage problems and ongoing flooding incidents in the Fens was carried out after a series of bad floods in 1936, 1937 and again in 1939, the Sir Murdoch MacDonald Report on Flood Protection published in 1940. Investment in flood prevention was, however, delayed by the Second World War. Following the very bad floods of March 1947 the MacDonald report was reactivated.
Vermuyden’s unbuilt solution
Despite Vermuyden’s 17th century large-scale drainage works, the Fens failed to remain dry, with bad flooding episodes happening regularly. This was not Vermuyden’s fault, since one of his proposals had simply never been built. His drainage map, published in 1642, clearly shows a planned catchwater channel to collect flood waters from three rivers to the east of the Fens (the then-called Mildenhall, Brandon and Stoke Rivers) and divert them via a relief channel to north of his planned Denver Sluice.
The 1940 MacDonald report recommended building just such a cut off channel, collecting water from the same three rivers, now named the Lark, Little Ouse and Wissey.
In addition, this report also recommended building a new Relief Channel to take their surplus flood water away from the Fens and up to Kings Lynn, as well as improving the existing Ten Mile and Ely Great Ouse rivers from Denver to south of Ely. Work on all three flood defence elements started in 1954 and finished ten years later, in 1964.
The Cut Off Channel’s functions
In short, the Cut-off channel was built to serve two functions:
- To relieve the River Great Ouse from the threat of rising floodwater
- To deliver excess water to reservoirs in Essex
Taken together, the two different uses of the Cut Off Channel serve to both keep Ely dry in winter and keep Essex wet in summer. Water flows northwards to prevent flooding during winter times, and flows southwards in summer times to deliver water in Essex.
Some amazing engineering has gone into ensuring that both functions can be carried out. The channel runs across 35 miles of fenland from Downham Market to Mildenhall, with numerous sluices along the way. The southern part also goes largely underground before arriving in Essex.
Great Ouse Cut Off Channel: northwards flow for Ouse flood protection
Since it is estimated that 40% of flood waters in the Fens come from the three eastern rivers (the Lark, Little Ouse and Wissey), the importance of the cut off channel for flood prevention becomes clear.
Map showing the Cut Off Channel, in relation to the Great Ouse and its tributaries, the Lark, Little Ouse and Wissey. Source: report Chris Holley, 2005.
When the Great Ouse Cut Off Channel is flowing northwards for Ouse Flood Protection, the water flows starts at the Lark Head Sluice on the River Lark at Barton Mills, when the sluice is opened. There are four weirs to control the water levels during the considerable fall between the Lark at Barton Mills and the Little Ouse at Hockwold.
At Stoke Ferry, the River Wissey flows in an aqueduct over the Cut Off Channel. Image by Chris Holley.
The Cut Off Channel then flows northwards and intersects the River Little Ouse at the Hockwold Sluice at Hockwold, and then intersects the River Wissey at the Wissey Sluice at Stoke Ferry, and thence to Denver Sluice.
Cut off Channel seen from A10, flowing west towards the Denver Sluice. Photo by Chris Holley
At each of these intersections, the Cut Off Channel goes underneath the Little Ouse and Wissey rivers in a siphon or U-tube, and can draw water from the two rivers when the appropriate sluice gates are opened and closed.
The Relief Channel starts at Denver and takes water from the Cut Off Channel through the Impounding Sluice, and/or from the Ely Ouse through the A G Wright Sluice, down to the Tail Sluice at Saddle Bow near Kings Lynn. The Relief Channel acts as an
additional flood water storage reservoir, which can be evacuated out to sea at
Section of the OS map showing where the Cut Off Channel joins other waterways at the Denver Sluice complex. Source: report by Chris Holley.
Close-up of Denver Sluice complex, showing the various waterways coming together at this important node. Source: report by Chris Holley.
Great Ouse Cut Off channel: southwards flow for Ouse-to-Essex water transfer
Essex regularly suffers from droughts in summer. In 1964 it was realised there was insufficient water to support expansion, development and growing consumer demand in south Essex. In 1968 it was proposed to reverse the flow and use part of the Cut Off Channel to take surplus fresh water southwards from the Great Ouse at Denver Sluice and deliver it down to existing reservoirs in Essex.
The Ely Ouse To Essex Water Transfer Scheme was completed in 1971, taking water down to Abberton Reservoir 87 miles south, and to Hanningfield Reservoir 90 miles south. Although existing watercourses are utilised for about two-thirds of the distance, a new tunnel and new pipelines and storage tanks all had to be built.
When the flow of the Cut Off Channel is reversed southwards for Ouse To Essex Water Transfer, water is diverted through the Diversion Sluice at Denver and flows up the Cut Off Channel, through the siphon under the River Wissey at Stoke Ferry, to Blackdyke Intake at Feltwell, between Stoke Ferry and Hockwold.
Representation showing the physical layout of the shaft at Blackdyke Intake, the tunnel, and the uptake shaft at Kennett Pumping Station. Source: report by Chris Holley.
Water is extracted from the Cut Off Channel at Blackdyke Intake, where it plunges 90 feet down a huge shaft into a long tunnel under the hills and under the A11 near Newmarket, to Kennett Pumping Station. At Kennett, water is pumped 280 feet up to the surface again, then by pipeline under the hills by the A14 to Kirtling Green Outfall and Kirtling Brook, where it joins the River Stour to Wixoe Pumping Station near Haverhill. From Wixoe Pumping Station, water flows by various means to three Essex reservoirs.
Want to know more?
If you would like to know more about the history of and engineering works along the Cut Off Channel, Chris Holley has produced a richly illustrated and detailed 92-page report, titled ‘Ely Dry – Essex Wet: the Great Ouse Cut Off Channel’. You can contact him for more information, or to purchase a copy through email@example.com
A synopsis of Chris’ report can also be downloaded here: Cut Off Channel Synopsis 2
Interpretation board at the Denver Sluice, explaining the origin and function of the Cut off channel. Image by Chris Holley.