Map disclaimer

This map is for indicative purposes only. It is intended as a general guide to provide an overview of flood risk and should not be used to assess flood risk for individual properties. While every effort has been made to ensure that data is accurate and reliable, we cannot assume liability for any damages caused by any errors or omissions in the data, nor as a result of the failure of the data to function on a particular system.

All intellectual property rights in the data and information contained in the map are owned by the council or are licensed from other third party data providers. Any 3rd party information shown on this map should be obtained directly from those organisations.

Any Government information used by the council can be obtained from the Environment Agency Customer and Engagement team for Hertfordshire and North London

The contents should also not be relied on in place of a site specific flood risk assessment that should be undertaken to accompany any planning application. 


This map provides an indication of the location of rivers within the London Borough of Hillingdon. The information is obtained from a collection of sources:

  • main river information is obtained from the Environment Agency.
  • ordinary watercourses and other ditches. These have been identified through a variety of methods, some of which have not been verified or checked

These rivers may be above or below ground, and there may also be further rivers not identified on this map. Please note that if your deeds show you own up to the top of a river bank you may be responsible for maintaining that river. For further information, please see guidance provided by Land Registry.

This map should not be used for site specific flood risk assessments or development proposals to determine the exact line and width or top of bank of any river. Rivers move and evolve over time and a site specific assessment should always be undertaken. However, for insurance purposes it can give an approximate distance to the nearest watercourse.

Thames Water outfalls    

These are shown as green triangles. This map provides an indication of Thames Water outfalls. This data has been obtained from Thames Water Utilities Ltd and is edited to show outfalls from the Thames Water surface water drainage network into rivers.

Flood risk from rivers

This map provides an indication of flood risk from rivers.

The Functional Floodplain (Flood Zone 3B)        

This zone is shaded light green. Flood zone 3b is defined by the Planning Practice Guidance. The zone comprises land where water has to flow or be stored in times of flood. This is identified by the council in their Strategic Flood Risk Assessment.

No development other than 'water compatible' or 'essential infrastructure' is appropriate in this zone.

Flood Zone 3A and 2

  • Flood Zone 1 is shown as clear and is all land outside Zones 2 and 3
  • Flood Zone 2 is shaded hatched dark blue
  • Flood Zone 3a is hatched light blue                            

The council uses the Government information shown on the 'long term flood risk assessment for locations in England' for modelled flood extents. You can view Flood Zones 3 and 2 on the Government website.

Surface water flood risk areas

This area is shaded purple. This map provides an indication of areas at risk of surface water flooding. The council uses the Government information shown on the 'long term flood risk assessment for locations in England' for modelled flood extents. You can view this on the Government website.  There are no amendments that the council have made to this mapping.

Critical drainage areas

This area is shown hatched dark purple. This map provides an indication of critical drainage areas. Critical drainage areas may be within Flood Zone 1 (little or no risk) but which has critical drainage problems. They include the catchment area that contributes to the critical drainage problems as well as the area which has the drainage problems. The council has identified these through the surface water management plan.

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Flood and water information map

Page last updated: 18 May 2022