Engineering London’s Lost Rivers

Polypipe Permavoid geocellular system

Polypipe Permavoid geocellular systemUsing sustainable drainage to manage the rivers beneath our feet

Innovative pilot project from Thames Water could provide effective solutions to urban flood risk areas.

Many homes in the Fulham and Hammersmith areas of London are at risk of flooding during heavy rainfall, due in part to their proximity to one of London’s legendary ‘lost’ rivers – Counters Creek.

Most of us are familiar with the Thames, but London is also home to several lesser-known lost rivers. Once flowing at ground level, these rivers have been slowly buried beneath the capital’s streets and buildings and now lie hidden beneath our feet. This was all part of Joseph Bazalgette’s drainage project following London’s “great stink”.

Counters Creek originally flowed above ground in West London before being diverted below ground to join the public sewer network in the nineteenth century. In more recent years, the area around Counters Creek has lost more than a fifth of its permeable green space and all its open water courses, leaving surface water run-off with nowhere to go. This increases the risk of flooding in the sewer system and, as many homes in the area have been built with basement levels, this poses a big problem for local homeowners.

Collaborative innovation

To address this issue, Thames Water teamed up with drainage engineers, environmental experts and the local council to implement an innovative sustainable drainage system.

The aim of the project was to retrofit new sustainable drainage schemes in three ‘typical’ London streets – Melina Rd, Mendora Rd and Arundel Gardens – to monitor and assess their effectiveness at reducing flood risk. This is a complex task which requires an experienced London drainage contractor to plan and implement.

Three approaches

While all three schemes use Polypipe’s Permavoid geocellular system – a system designed to limit the flow of excess water into the sewer network – each has followed a slightly different approach, taking local environmental factors into account.

Melina Road has implemented a ‘green’ solution which, as well as mitigating the risk of flooding, also helps to encourage plant growth and provides an additional green space for the local community. This approach involved installing four storage tanks, containing Permavoid Permafoam cells, beneath the area’s rain gardens. These tanks store excess water during heavy rainfall and this can then be used to irrigate the plants and vegetation growing above.

Mendora Rd took a slightly different approach by installing Permavoid cells underneath the paving on either side of the street. During a storm event these cells can hold over 130 cubic metres of water. A Permafilter geomembrane ensures that the water is treated for oil and other pollutants before it reaches the storage tank.

The Arundel Gardens section of the scheme is due to be implemented this month. In this instance, Permavoid will be installed beneath the surface of the road and provide storage for rainwater. This stored water can then be used to irrigate the magnolia trees that line the sides of this Kensington street.

As part of their design and implementation, all three schemes have demonstrated a commitment to preserving the area’s biodiversity and maintaining quality of life for the residents.

Futureproofing our cities

This project is a great example of successful collaborative working and highlights the benefits of retrofitting flood defences. With climate change making extreme weather events ever more common, it’s important that we take urgent steps to minimise urban flood risk. With this in mind, sustainable drainage systems could be the solution we’re looking, helping us to protect our cities, both now and in the future.