Section B - flood risk
Westminster is a lead local flood authority and responsible for managing local flood risks in the city i.e. risks of flooding from surface water, ground water and smaller watercourses.
The city is divided into three flood zones. Zone 1 covers the majority of the borough, which has the lowest probability of flooding, zone 2 has a medium probability of flooding and zone 3 the highest probability of flooding, including the floodplain. This map shown in the City Plan (Page 136, Figure 29) shows that the highest risk of flooding in (zones 2 and 3) are in the south east of the borough. A number of surface water flood risk hotspots are also identified across the city and can be found in the Strategic Flood Risk Assessment.
Westminster is fortunate to be defended from tidal and fluvial flooding by the Embankment flood wall. Responsibility for maintenance and repair of the flood wall sits with the council, and the relevant landowners who we partner with, alongside Thames Water and the Environment Agency to ensure that the appropriate standards are maintained.
Changes in climate are predicted to have a significant impact on future flood risk. Westminster is protected from the Thames by the Thames Barrier and associated Thames Tidal Flood Defences as well as the Embankment wall.
Surface water flooding
When rainwater does not drain away either by soaking into the ground or through the drainage system on roads and around buildings, surface water flooding builds up. Landscaped areas and planting are important ways to incorporate sustainable drainage into urban environments. Sustainable drainage can help:
- reduce the quantity of water (flooding)
- slow down the speed of water run off (attenuate)
- soak up surface water (infiltrate); and
- when accompanied with good design can channel water to appropriate areas for drainage (convey)
Surface water flooding whether it falls on to your property or the highway drains away into the public sewerage system which in Westminster is managed by Thames Water. Westminster has responsibilities as the highways authority to ensure that kerbs and gullies, gratings, grids, channels and ditches let water flow freely into the sewerage system.
For new developments, the Strategic Flood Risk Assessment (SFRA) provides detailed information on the risk of flooding in the borough, the way that the city is defended and the requirements for developments that need planning permission.
A Green Infrastructure Strategy will be forthcoming that will set out the council’s priorities for green infrastructure, urban greening, playing pitches trees and biodiversity priorities for a climate resilient city.