The Environment Agency’s £12M Flood Alleviation Scheme on the River Douglas in Wigan, UK, is nearing completion, following the installation of two giant Hydro-Brake Flow Control devices from Hydro International. The 2m diameter Hydro-Brake’s are the centrepiece of an 8m high, 120m wide and 120m long dam constructed by main contractor Galliford Try in an 80-week contract.
The dam has created a potential 370,000m3 of flood storage extending along a kilometre of the Douglas valley. After six years of planning, the scheme now provides increased protection with just a 1% chance of flooding from the river in any given year.
In the event of a major flood, water would be held behind the dam to reduce the chance of flood defences in Wigan being overtopped. The excess water would then be stored in the valley upstream from the dam. After a flood, the stored water would be slowly released back into the river until normal river levels are achieved.
“Constructing temporary flood storage was the clear solution in such a narrow, steep-sided valley. The site was fortuitously close to the town centre and on undeveloped land,” said Environment Agency Project Manager Eddie Goddard. “The use of Hydro-Brake Flow Controls was vital because it has enabled the dam to be fine-tuned. We were able to reduce the reservoir footprint significantly, compared to a conventional flood gate solution.”
Consultant Engineers Jacobs and the Environment Agency worked closely with Hydro International over many months using both physical and computer-aided modelling to ensure the Hydro-Brake Flow Controls were precision engineered to optimise the storage capacity.
The Wigan flood storage project was the second phase of the Environment Agency’s flood alleviation scheme at Wigan. Phase one, completed in 2008, involved the raising of defences along the River Douglas.