Two Hydro-Brake® Flood flow controls provide flood protection to over 600 properties in Wigan, cutting flood risk to 1%.

Situation

The town of Wigan, UK was hit by flooding on average twice a year, and had been suffering from floods for more than 30 years.

Problem

Over 600 properties in Wigan were exposed to flood risk from the River Douglas and its tributaries every year.

Solution

The UK Environment Agency implemented the Wigan Flood Alleviation Scheme, a £12M, two-phase flood protection project that incorporated embankments, flow controls and temporary flood storage, designed in a way that blended engineered solutions with natural features to provide optimal flood protection.

Phase 1

The first phase of the works involved the construction of new and raised flood defence walls and embankments on the River Douglas through central Wigan. The first phase of the scheme raised the standard of protection to 1 in 20 years, or 5% risk of flooding in any one year.

This phase included the construction of a kilometre (0.6 mi) of reinforced concrete flood walls as well as 300 m (328 yds) of earth embankments.

Phase 2

The second phase of the works involved the construction of a 150 m (164 yd) long, 8 m (26 ft) high earth dam across the River Douglas Valley, forming an upstream storage reservoir, and a new 100 m (109 yd) long concrete culvert constructed beneath the dam.

Inside that culvert two Hydro-Brake® Flood flow controls provide precisely designed flow control to hold back flood water and store it upstream, protecting downstream properties from flood damage. This further increased the standard of protection to 1 in 100 years, or 1% risk of flooding in any one year.

The Phase 2 works also involved the creation of a habitat enhancement area immediately downstream of the storage reservoir, which included the creation of ponds and the planting of thousands of trees and shrubs.

Outcome

The dam has created a potential 400,000 m³ (105 million gallons) of flood storage extending along the Douglas valley, and the Hydro-Brake® Flood flow controls use this flood storage to prevent flood waters from reaching Wigan. 

The flood alleviation system now provides greatly increased flood protection, with just a 1% chance of flooding from the river in any given year.

The system put to the test

In June 2012 heavy rain put the system to the test for the first time.

The Flood Alleviation Scheme was designed to protect 610 properties downstream in Wigan town centre," said Keith Roddy, Project Team Manager for the Environment Agency. "The scheme did its job successfully and significantly reduced the extent of flooding, protecting homes and businesses previously at risk. More than 100 mm of rain, equivalent to one month’s rainfall, fell in just a few hours in the North of England during the weekend of 23 and 24 June. Over 3,000 homes were protected from flooding by Environment Agency defences, including those at Wigan."