Surface water flooding

Surface water flooding, sometimes called pluvial flooding, occurs when intense rainfall exceeds the capacity of surface water drains, soakaways and watercourses to remove run-off, causing water to pond on roads, driveways and gardens. In Greater London the issue is closely linked to increased hard surfacing of front gardens, undersized historic drainage and combined sewers reaching capacity during storm events. The Environment Agency maps flood risk by surface water, and the SuDS approach is now central to managing run-off from new and altered developments. Building Regulations Part H3 and the Non-statutory Technical Standards for SuDS set out expectations for design. Engineers usually address common causes by clearing existing drains, repairing soakaways, installing permeable paving and considering attenuation tanks for sites with limited soakaway capacity.