Limiting the risk of disruption due to flooding

Project Scope

Carry out a Flood Risk Assessment (FRA) of a proposed development involving the conversion of 40 properties into 20 self-contained houses for social housing stock. The site is located 75 metres from the river Thames and within Flood Zone 3 on the Environment Agency (EA) Flood Map for planning. It is also within an Area Benefitting from Defences (ABD). The report assessed the potential flood risk to the site, the impact of the impact of the proposed development on flood risk elsewhere, and mitigating measures that could be taken to ensure the lifetime safety of the development.

Tools For Implementing Tasks

The FRA reviewed and assessed relevant flood risk data, including EA online flood maps, British Geological Society interactive map, MAGIC interactive map, West London Strategic Flood Risk Assessments for Hounslow and its surrounding boroughs, and the London Borough of Hounslow Local Flood Risk Management Strategy.

Challenges For Implementing Tasks

The EA Climate Change Guidance was last updated in 2016, which meant data shown on the EA Flood Map for Planning and the EA Long-term Map didn’t take into account the implications of climate change. As the site is located within Flood Zone 3, further work may be needed to accurately determine flood risk.

Solutions

Solutions risk of the site flooding from all sources, including tidal, surface water and artificial, was assessed and considered to be low. In the event of extreme flood events or an undefended tidal event, the following mitigating and resistance measures were recommended:

  • Raise the ground floor as high as possible
  • Limit all sleeping accommodation to the first floor and above
  • Safe internal access to the first floor in all properties
  • Raise electronic control units and sockets as high as possible
  • Use solid flooring at ground floor level
  • Install smart air bricks or air brick covers
  • Use non-hygroscopic renders where applicable
  • Install flood guards to all doors
  • Seal cable entry points
  • Use plastic and stainless-steel fixtures and fittings, and avoid wooden alternatives.

Key Achievements

The FRA found that there is a low risk of the development site flooding. However it also highlighted that although the site is within an area protected by the Thames Tidal Defences, there is a residual risk of overtopping or a breach of the defences. It also identified measures that can be taken to ensure the safety of the residents and long-term safety of the development.

Benefits For Clients

The detailed FRA focuses specifically on the client’s proposed development, taking into account its location and scope of work. It provides the client with a list of mitigating and resistance measures, as well as further recommendations to ensure the long-term safety of the site. These include updating the report with EA Product data and producing a Flood Warnings and Evacuation Plan for residents.