The following flood risk zones should be used to inform:

  • site-specific flood risk assessments (FRAs) prepared by developers in support of their planning applications, and
  • as the basis for undertaking the ‘sequential test’

View the EA’s interactive ‘Flood Map for Planning (Rivers and Sea)’

Flood risk zones

  • Flood Zone 1 ‘Low Risk’ (less than 1 in a 1000 annual probability of flooding);
  • Flood Zone 2 ‘Medium Risk’ (between 1 in a 100 and 1 in a 1000 annual probability); and
  • Flood Zone 3 ‘High Risk’ (over 1 in a 100 annual probability).

More detailed maps are shown in Figure 4.1 (with insets 1 and 2) of the Strategic Flood Risk Assessment (SFRA). These cover:

  • areas at risk of river flooding,
  • the extent of the ‘functional flood plain’ (Flood Zone 3b),
  • areas benefitting from flood defences,
  • flood storage areas and
  • the location of rivers and ordinary watercourses within the Borough

Surface Water Flooding

View the EA Updated Flood Map for Surface Water.

The EA’s Updated Flood Map for Surface Water (uFMfSW) identifies the following categories of risk:

  • ‘very low’ risk (less than 1 in 1000 annual probability);
  • ‘low risk’ (between 1 in 1000 and 1 in 100 annual probability);
  • ‘medium risk’ (between 1 in 100 and 1 in 30 annual probability);
  • ‘high risk’ (more than 1 in 30 annual probability).

You can view detailed maps showing:

  • areas at risk of surface water flooding and
  • drainage catchments within the Borough

These are available in figures 4.2 and 4.3 of the strategic Flood Risk Assessment (SFRA). The location of ‘critical drainage areas’ (CDAs) is shown in Figure 1 of the Borough Surface Water Management Plan (LBS, 2011).

Groundwater Flooding

Figure 4.4 of Sutton’s SFRA Level 1 Report shows areas susceptible to groundwater flooding. This is based on British Geological Survey data.

Sewer Flooding

Except for combined sewers in the Hackbridge/Beddington area, most of the Borough is served by separate foul and surface water sewers. These are owned and maintained by Thames Water Utilities Ltd.

Surface water sewers are typically designed to deal with a rainfall event with up to a 1 in 30 annual probability of flooding. Figure 4.5 of the SFRA Level 1 Report, the Wards of Worcester Park, North Cheam, Rosehill and the northern part of Carshalton have been more affected by sewer flooding than elsewhere.