Kent County Council is working on a project in Margate to reduce the risk of flooding and the impact of increasing summer temperatures. Over 30 new trees have been planted across two urban residential streets, 11 of which are planted within specialist sustainable drainage (SuDS) tree pit systems. The project contributes towards reducing heat stress and surface water flood risk while also providing attractive spaces for residents, visitors and wildlife.
The challenge
Rising summer temperatures and resulting impacts from heat stress are an increasing concern across Kent, especially during heatwaves. The two residential streets in Margate selected for the project suffer from heat stress during the summer and form part of the catchment that contributes to surface water flooding during heavy rainfall.
The solution
A study commissioned by Kent County Council recommended the retrofitting of specialist SuDS tree pits in the highway verges of the two residential streets to help reduce the risk of flooding.
By working bi-laterally across the Council, we identified an opportunity to develop a scheme combining the retrofitting of SuDS tree pits with conventional tree planting along the two streets. This helps to mitigate the impacts of increasing summer temperatures by planting a network of trees to increase canopy cover, providing shade during the summer months, whilst also reducing surface water flood risk in the catchment.
Over 30 trees have been planted along the streets, 11 of which are installed in specialist SuDS tree pits. The tree pit systems are placed in the existing highway verges, which will help manage surface water flood risk by receiving water directly from the adjacent highway and infiltrating it into the ground slowly, increasing the capacity of the combined sewer network and supporting sustainable water management.
The top of each tree pit system has been planted with an appropriate tree for the conditions they will experience. The species of trees, a mixture of Maples and Maidenhair trees, have been selected for their:
• canopy size - to generate shade
• ability to withstand periods drought and heavy rainfall
• biodiversity benefits.
The impact
It’s estimated that prior to the scheme being implemented, the drainage system along the two streets was only capable of draining rainfall events up to the 5-year return period. The SuDS tree pits designed and installed in the scheme can cover rainfall events up to a 30-year return period. Surface water is now intercepted from a total of 2,200m2 of highways and pavements, which equates to approximately 30% of the overall water catchment. This additional capacity will reduce flood risk to 30 properties in the catchment in Margate, improving the local drainage of the area by reducing the number of properties affected by flooding.
The mixture of Maple and Maidenhair trees planted provide shade and help to reduce the air temperature during heatwaves. Increasing the number of trees can cool the air temperature in urban areas. This happens because the leaves reflect back sunlight and provide shade during the summer months, but also through evapotranspiration. This is a natural process in which the sun's energy transfers water from the tree leaves into the atmosphere, which can help to cool the air temperature during heatwaves.
The trees planted have been chosen to help provide essential food and habitat for local wildlife; their seeds and nectar will be a valuable food source for birds, butterflies, and other insects as well as a place to lay their eggs.
Increasing the network of urban trees in residential areas can increase property values, improve visual and physical amenity and contribute to noise abatement. In addition to contributing towards public health outcomes, the scheme has enhanced the amenity value of the area with the rejuvenation and improvement of existing grass verges in the two streets.
How is the new approach being sustained?
Through the Interreg 2 Seas Cool Towns Project, Kent County Council has funded the works to install the 11 specialist tree pit systems within the two residential streets. The purchase of the trees was funded by the DEFRA Urban Tree Challenge Fund.
During project implementation key stakeholders have been engaged to ensure the needs of the scheme and stakeholders including residents and visitors are met. Daily users of the space benefitting from the scheme include residents, visitors and those using the streets as a thoroughfare to access nearby amenities including bus stops, care facilities and schools and nurseries.
Lessons learned
This scheme is an example of how multi-functional climate adaptation projects with cross-cutting benefits can be developed and implemented by working bi-laterally within organisations. The scheme demonstrates how retrofitting specialist SuDS tree pits and conventional tree planting in an urban area can be combined to gain multi-functional outcomes for mitigating the impacts of increasing summer temperatures and alleviating surface water flood risk whilst improving biodiversity outcomes and creating attractive spaces for residents and visitors.