Eye Brook Reservoir Overflow
Eyebrook Reservoir lies on the border between Leicestershire and Rutland, near Caldecott. It was constructed between 1937 and 1940 by Stewarts & Lloyds to provide a dependable water supply for their large steel and tube works at Corby. The reservoir was created by building an earth dam across the valley of the Eye Brook, with the first water being supplied to the steelworks in December 1940.
The reservoir became an important wartime asset because the Corby works produced steel and tubes essential to the war effort. In 1943, it gained another place in history when 617 Squadron RAF, the famous Dambusters, used Eyebrook for low-level flying practice before the raid on the Möhne, Eder and Sorpe dams in Germany. Lancaster bombers repeatedly practised over the reservoir in the weeks before the raid.
Of particular interest is the reservoir's overflow or spillway. The original structure was a large bellmouth spillway, approximately 18 metres long and 12 metres wide. It was designed to safely discharge excess water through a diversion tunnel beneath the dam and into a concrete channel downstream.
In 1955, engineers increased the reservoir's capacity without rebuilding the main earth dam. They installed 16 ferro-concrete, self-priming siphons around the existing bellmouth spillway. This raised the normal water level by approximately 76cm and increased the storage capacity from approximately 6.91 million cubic metres to 8.09 million cubic metres. The work began in April 1955 and was completed in October of the same year.
The modification is particularly interesting because it provided substantially more storage while retaining the existing dam and its flood-discharge arrangements. The siphon system automatically came into operation as the water reached the raised level, allowing excess water to pass safely through the spillway system.
Today, Eyebrook Reservoir is valued for its wildlife, fishing and landscape, and is designated as a Site of Special Scientific Interest. The reservoir, dam and unusual siphon overflow remain fascinating examples of industrial and civil engineering from the twentieth century.
