We are working with project partners including Thames Water, the Environment Agency, and Network Rail on a two-year flood alleviation study for Raynes Park. Following a successful joint funding bid, all project partners have made financial and resource contributions to this study, which started in spring 2024 and will conclude in spring 2026. The study aims to see if it is feasible to alleviate flooding in the area and what would be required to do so. If deemed viable, later phases of the project will look to secure funding to deliver these improvements, which may be implemented in combination with other public realm enhancements to improve the town centre.
Why the study is needed
The Raynes Park catchment has experienced flooding almost every summer over the past 15 years. There was significant rainfall in the summer of 2021 which resulted in flooding to infrastructure and over 120 properties. Historical reports detail that the flooding has occurred from both the surface and the foul water sewer networks as well as fluvial (river) flooding from the Beverley Brook and Pyl Brook.
What we have done so far to reduce flood risk
Following the significant flooding in the town centre in summer 2021, Merton Council’s flood risk engineers have worked in partnership with Thames Water and have delivered several interventions to reduce flood risk in Raynes Park. These include:
- below-ground surveys,
- upgrading of highway drainage in the town centre,
- a new sustainable drainage system (SuDS) raingarden on Coombe Lane/Pepys Rd to reduce some flows to the railway underbridge, and
- installing 4G gully sensors to measure silt and water levels.
New and upgraded pumps were installed under the railway bridge on Approach Road. Thames Water has removed of significant quantities of silt (over 21 tonnes) from the surface water sewer network, which means the capacity of the surface water network in the town centre is once again full utilisable. Thames Water have recently completed a full line clean and survey of the over 3km of main sewer and culverts from the town centre to the discharge point with the Beverley Brook.
Flood modelling
As part of the study, an integrated hydraulic model is currently being built of the Raynes Park catchment area. The model will include information from river, drainage and sewer assets owned by Merton Council, Thames Water, the Environment Agency, and Network Rail. The model will help to understand the different flood mechanisms within the catchment and how the various assets (surface water sewers, track drainage, highway drainage and Beverley Brook) interact during the flood events. The model build draws data, expertise, and information from a wide range of specialist subject areas including surveying, hydraulic engineering, and hydraulic modelling. The extent of the catchment boundary is subject to change depending on the hydrology of the catchment as the project progresses.
The model will be used to understand where the flood risk is greatest in the catchment, what is the root cause of flooding and what options there are to reduce the flood risk. These options will be evaluated in the model to identify their effectiveness with the most effective solutions being presented to the partners for future consideration.
Project timescale
Following the modelling phase, the partners will conduct an analysis of the presented options, assessing their feasibility, cost-effectiveness, and alignment with each partner’s long-term strategic objectives. The analysis will determine feasibility of delivery through standalone projects or partnership funded projects.
The initial modelling phase of the project is scheduled to be completed in winter 2024/2025, with the next phase is expected to be rolled out in 2025.
