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    What is the Risk of Flooding from Surface Water?


    Surface water flooding happens when rainwater does not drain away through the normal drainage systems or soak into the ground, but lies on or flows over the ground instead. Managing the risk of flooding from surface water is the responsibility of lead local flood authorities (LLFA). The LLFA is the unitary authority or if there is no unitary authority, the county council for the area.

    The Environment Agency (EA) is responsible for publishing surface water flood risk maps however mapping of surface water flood risk areas is responsibility of LLFAs. We, the EA, produced the Risk of Flooding from Surface Water (RoFSW) map on behalf of LLFAs, using their input and information. It assesses flooding scenarios as a result of rainfall with a 3.3, 1 and 0.1 percent chance of occurring each year. Although surface water flood risk information is not suitable for identifying whether an individual property will flood it does gives an indication of the broad areas likely to be affected.

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      Elena Cabo

      Do the RoFSW_TQ18_Depth_1in100 layers consider Climate Change allowances? Which layer could I use to consider them?

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      Data Services Platform team

      Thank you for your question. The RoFSW data relates to the current level of risk, LLFAs are responsible for managing surface water flood risk and we publish the maps on their behalf. We don’t hold any Climate Change RoFSW data.

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      Christopher Barry

      I am interested in the blue square map: what are the meanings of the fields "numpeople" (total people or just those at risk?) "numresp", "numnonresp" and "numkeys"? Does the RoSWF include the risk from rivers bursting their banks, or is it just from rainwater not draining?

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      Data Services Platform team

      Thank you for your question.

      The indicative flood risk areas or “blue squares map” were only preliminary and have since been superseded by the finalised flood risk areas here:
      The above dataset is just the spatial areas. If you are interested in numbers at risk, the new interactive flood risk maps, can be used:

      Both of the above come with guidance as to what the data is and how to use it.

      The RoFSW maps just include surface water and not combine with rivers and sea.

      I hope this helps
      Ella Fotheringham
      Environment Agency