Flood Defence
LATTENBURY SERVICES ‘Caring for the
Countryside’
Watercourse Management
“This means that a great deal more river water can flow through the dam before the need to start attenuation. As a result, significantly less storage is required.”
To precisely engineer the flood storage area, teams from Jacobs and the Environment Agency worked closely with Hydro over many months. A physical model was built and subject to extensive testing as well as applying Computation Fluid Dynamics techniques to model the flows precisely confirming the performance of the dam under varying flow parameters.
A new design of Hydro-Brake® Flow Control with an adjustable intake was also developed specifically for the project by Hydro in close co-operation with Jacobs and Environment Agency teams. The addition of specially designed restrictor plates on the Hydro-Brake® Flow Controls’ intakes will enable the median 10,000 litres per second flow rate from the outfall to be adjusted by plus or minus 20% in future.
The new design will enable the flow of the river downstream to be adjusted in future to take account of climate change, or to alter the outflow based on ongoing experience. The Environment Agency is continuing to monitor river flows closely.
Construction
The cone-shaped Hydro- Brake® Flow Controls weighing 15 tonnes each were installed into the dam using a 200-tonne crane.
Main contractor Galliford Try moved some 70,000 tonnes of earth to create the dam and flood storage area, including a stilling basin immediately upstream of the dam.
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Construction challenges included the specialist removal of tonnes of Japanese Knotweed and the investigation and ground stabilisation of nearby coal mining sites.
The inlet to the dam is protected by a series of debris screens and a specially- designed debris screen capable of withstanding loads of 50 kilonewtons.
Extensive landscaping works and the creation of an access road and car park has helped to restore the public amenity value of the valley area for local residents. The spillway of the dam was covered in Grasscrete to encourage rapid ‘greening’ of the site.
Alex Stephenson, Stormwater Director of Hydro International said:
“Whilst not quite as big as the Hydro-Brake® Flow Controls installed as part of the Glasgow Flood Prevention Scheme last year, the Wigan scheme is still one of the largest, and certainly the most innovative flood storage projects to date.
“Hydro’s design and modelling teams worked closely with the Environment Agency and Jacobs to provide a unique solution for Wigan, which could have major benefits for future flood alleviation schemes, “he added.
“A completely new design of Hydro-Brake® Flow Control has resulted, incorporating in-built adjustability that can be used on any scheme from the biggest like Wigan to the more typical drainage and sewerage schemes”.”
Client: Environment Agency Consultant: Jacobs Engineering Contractor: Galliford Try
For more information about Hydro-Brake® Flow Controls or any of Hydro’s sustainable solutions for stormwater control and
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