OR/15/016 Introduction

McKenzie, A A, Ward, R S. 2015. Estimating numbers of properties susceptible to groundwater flooding in England. British Geological Survey Internal Report, OR/15/016.

Groundwater flooding is flooding where the pathway for water reaching a receptor, whether a building or other infrastructure, is through flow in the subsurface. Under extreme conditions groundwater recharge from rainfall, or from infiltrating streams and drains, raises groundwater levels in the lower parts of catchments to such an extent that groundwater either impacts buried infrastructure such as sewers and basements, or spills out onto the surface where it can cause problems in-situ, or further down gradient as water flows overland.

Groundwater flooding has only been explicitly recognised as an issue distinct from pluvial and surface water flooding over the last two decades, with the major floods of 2000/2001 giving an impetus to studying and mapping groundwater floods and flooding susceptibility.

A DEFRA sponsored study

Following a renewed and extended episode of groundwater flooding in Southern England in the spring of 2014, the Environment Agency and BGS have revisited the estimates of the number of properties that are in areas with a groundwater flood hazard, with the aim of providing better estimates in a similar way to those prepared for flooding from rivers, the sea and surface water.