Mason & Townsend House | Flood Risk Assessment for Southwark Council


FPS were instructed by Southwark Council to prepare the Flood Risk Assessment for the Mason House & Townsend House new homes redevelopment options. This included the demolition of existing garages and the construction of four storey and five storey buildings providing 18 residential apartments (two x 1-bedroom units, nine x 2-bedroom units, seven x 3-bedroom units) with associated estate-wide hard and soft landscaping, cycle parking and refuse storage and the replacement of the existing substation.

The EA Flood Map for Planning indicates the sites are located within Flood Zone 3. Flood Zone 3 is land assessed as having a greater than a 1 in 100 (>1% Annual Exceedance probability – AEP) chance of river flooding in any given year. The Flood Map indicates the sites benefit from flood defences. The flood defences provided protection to the sites up to a 1 in 1,000 year combined fluvial and tidal flood event.

Exception Test

As part of the Flood Risk Assessment, an Exception Test was conducted which was considered to be passed as the development comprises redevelopment of a currently low-value sites. The development will regenerate the sites and improve the aesthetics of the site to the benefit of the local area. Within a flood risk context, the Exception Test is considered to be passed by raising the Finished Floor Level of all ground floor accommodation to 2.65m aOD, which is 300mm above the estimated Maximum Likely Water Level at the sites during a potential breach of the Thames Tidal Flood Defences in the 2100 scenario. A surface water drainage design will be developed to ensure run-off from the sites is significantly reduced when compared with the existing sites. Flood resistance and flood resilience measures can also be implemented within the design to ensure the development can manage the risks should flooding ever occur.

A successful Exception Test should clearly show the development’s sustainability advantages to the community outweigh its flood risks. Additionally, evidence must be provided that the development will not only be safe throughout its lifetime, considering flood risks and user vulnerability, but also not heighten flood risk in other areas.

The Flood Risk Assessment demonstrated that the proposed development:

  • Is suitable in the location proposed.
  • Is unlikely to place additional persons at risk of flooding.
  • Is unlikely to increase flood risk elsewhere through the loss of floodplain storage, impedance of flood flows or increase in surface water run-off.

In collaboration with our esteemed team of flood risk consultants, Southwark Council has adeptly maximised the development potential of a critical site, navigating through its complex planning challenges. Despite encountering obstacles, we are thrilled that planning approval has been granted, paving the way for the project’s progression. At FPS, we are dedicated to crafting proposals that strike a balance between maximizing sustainable development, and ensuring paramount flood risk safety for properties and their occupants.

Result: Permission Granted ✅

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