Susceptibility to groundwater flooding

Susceptibility to groundwater flooding for the Oxford area.

Groundwater flood susceptibility dataset can be used when planning.

In recent years it has been recognised that there needs to better understanding of the risk from groundwater flooding.

This has been due both to the occurrence of major flooding events clearly caused by groundwater and the inclusion of groundwater flood risk assessment in European and national legislation.

The British Geological Survey identified the need for a dataset that would allow stakeholders to assess the potential for groundwater flooding to occur in an area.

Local knowledge of groundwater flooding is patchy and can be unreliable, and often groundwater flooding is not identified as a distinct event, being masked by surface water floods.

The dataset we have developed shows where groundwater flooding could occur — defined by the term susceptibility — but does not indicate risk, that is the likelihood that it will occur.

Uses of the dataset

Since it was launched the dataset has proved to be useful for local authorities and developers for planning purposes as it identifies where further investigation is needed to assess whether groundwater flooding may affect property or infrastructure.

The dataset also forms a component of homebuyer reports, licensed and repackaged by value added resellers, which identify the potential for a range of hazards at the location of individual properties.

In 2010, the dataset formed the basis of maps included within the guidance issued by the Environment Agency to Lead Local Flood Authorities to help them produce the preliminary groundwater flood risk assessments required of them by flood regulations.

Definition of groundwater flooding

Groundwater flooding is defined for the purposes of our dataset as the emergence of groundwater at the ground surface away from perennial river valleys or the rising of groundwater into man-made ground under conditions where the 'normal' range of groundwater levels and groundwater flows is exceeded.

The method used to create the dataset attempts to identify locations where this form of groundwater flooding could happen.

It does not incorporate anomalous discharge from springs leading to groundwater flooding down the topographic slope or flooding associated with urban groundwater rebound, mine water discharge, urban drainage, or any other flooding associated with changes in the engineered environment.

Flooding models

Two hydrogeological conceptual models have been used in the development of the susceptibility dataset. These are permeable superficial deposit flooding and clearwater flooding.

Based on the conceptual models, a GIS rule-based approach was used to map the groundwater flooding susceptibility.

Different sets of rules were used for each of the groundwater flooding scenarios and the results were combined into a single groundwater flooding susceptibility dataset, available as a 50 m grid.

More about the Susceptibility to groundwater flooding methodology.