Built in the 1990s by Persimmon Homes, the 1900-home Elvetham Heath development at Fleet in Hampshire in a shining example of SuDS.(Sustainable Drainage Systems).

Acclaimed as a national example of good practice, the project was featured in the UK Government’s seminal Response to the Pitt Review, the forerunner of the Flood and Water Management Act.

Although not mentioned in the feature, part of the success of the SuDS scheme is due to 18 precast Hydro-Brake Flow control chambers, installed to protect against surface water flooding and to protect an area of the site designated as a nature reserve both during and after construction of the project.

With rare fauna growing in the area, the nature reserve is identified as being sensitive to nutrient overload, flooding and sediment, so a way of regulating the surface water runoff into this area was crucial.

The Environment Agency required a runoff rate from the impermeable surfaces of 2.72 litres per second per hectare (106 gallons per minute per acre), representing a 1 in 50-year event, which was standard in the 1990s.

As land for large swales and pond, containment was not feasible; the precast flow control solution of 18 Hydro-Brake chambers provided balancing and buffering of the surface water runoff and were placed strategically to attenuate the flow control of surface water. This meant that lower levels of the site the discharge into the watercourse were not overloaded.

Ryan Lundy, Senior Civil Engineer for Bradbrook Consulting worked on the design: “People see the numerous swales and large ponds when walking or driving around Elvetham Heath but probably don’t appreciate that many of them are interconnected. The strategically placed Hydro-Brake® Flow Controls provide balancing and buffering of the surface water runoff. Across the whole site the runoff is regulated by gravity and the storm water drainage strategy is achieved without the use of pump stations”.

“The drainage system is performing well and we have not been aware of any flooding incidents, despite severe stormwater conditions in the South of England including in 2007,” he added.

“In addition, its hydraulic efficiency ensures that the space required upstream to provide the required storage volume is reduced.”

Paul Whyte, Commercial Director at Marshalls Civils & Drainage commented, “Flooding in the UK is a major problem, combining our technical knowledge of water management solutions and SuDS can mean the success of a project. This development provides a great example of how the combination of engineered solutions and good practice can be applied to engineer in nature’s way.”