Opportunity
Counters Creek sewer runs through Kensington, Earls Court and Chelsea before joining the Thames. Severe storms in July 2007 caused the sewer to flood the basements of about 1700 properties. Since then, the London boroughs of Chelsea and Kensington and Hammersmith and Fulham have been working with Thames Water to address this problem and ensure residents and businesses are protected against flooding.
Solution
The Counters Creek flood alleviation scheme involves improvements to local sewers and the installation of FLIP units (pumped non-return valves) at individual properties and sustainable drainage systems (SuDS) on six roads in Hammersmith and Fulham. To determine the best solution, our team used a catchment model to allocate each property a risk score and root cause of flooding, assigning and grouping the different options so areas that would see the greatest benefit could be prioritised. The team reviewed the assumptions in the model and gathered more catchment performance information through surveys. We also worked with Thames Water and Thames Tideway to develop an innovative way to demonstrate the future performance of the different elements.
Half the SuDS schemes combine permeable pavement and nature-based solutions. Rain gardens and tree pits were integrated into the overall design for these three roads to supplement the block permeable pavement parking bays constructed on both sides of the highway. These biodiversity pockets, generally 2m x 2m, are located at dead spots or discreet locations on the longest roads.
Community engagement was essential to the success of the project, with on-street consultation events led by Thames Water and the London Borough of Hammersmith and Fulham, along with letter drops. These found that residents were mostly supportive of green infrastructure but did not want to lose parking spaces. This feedback not only influenced the final design of the SuDS but the installation of other improvements to the area by the council, including sinusoidal speed humps and renewed footways. At the end of the construction work, planting days were organised by the Hammersmith Community Gardens Association on the streets with rain gardens.
Outcome
The SuDS solutions aimed to address the four pillars: water quantity, water quality, biodiversity and amenity. Since work was completed in March 2020, the solutions have successfully reduced surface water runoff entering the combined sewers and flooding basements during periods of heavy rainfall. The rain gardens and tree pits are attractive new features that improve the streetscape. The local community continues to be involved, with maintenance of the green spaces undertaken by the Hammersmith Community Gardens Association, encouraging resident ownership and pride in their street.