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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.

The following guidance "What is the RoFSW" provides more detail on the whole dataset, including explanation of output flow characteristics such as depth (Section 7.3)

(https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/842485/What-is-the-Risk-of-Flooding-from-Surface-Water-Map.pdf)