The use of elevation models to predict areas at risk of groundwater flooding

Abstract

Groundwater flooding, which occurs when the groundwater table rises in response to exceptional recharge rates either to the ground surface or to a point where subsurface infrastructure is affected, has been recognized as a significant issue with real economic impacts.A methodology has been developed to produce maps of groundwater flooding susceptibility, using geological and hydrogeological data. While good geological map data are available in digital form for England and Wales, there are much less data on water levels. These levels are usually measured during the construction of water boreholes, and while there is a national groundwater level monitoring network for regulatory purposes, at a national level data are sparse. To assist in developing a comprehensive map of water levels, the British Geological Survey (BGS) has adopted a number of strategies for data interpolation for areas with limited water level data and a surface has been derived from a terrain model by considering interactions between groundwater and surface water in rivers and lakes. When comparing the calculated levels against the available field measurements, a high correlation was found to exist. However, it was considered that in areas where bedrock aquifers dominate, this interpolated surface was probably inaccurate, and so refinements were developed to improve the modelled water levels surfaces.The resulting groundwater levels have been used to develop maps of areas where shallow groundwater may pose a risk. With potential changes in groundwater recharge postulated as a result of global climate change, identifying areas prone to flooding from groundwater, or areas where groundwater is likely to increase the impact of surface water flooding, is increasingly important.

Groundwater flooding within an urbanised flood plain

“…A national assessment of groundwater flood susceptibility undertaken by the British Geological Survey (McKenzie et al, 2010) includes the River Thames flood plain in the Oxford area within its 'very high' category, that is, it has mapped the underlying superficial geology as permeable and the groundwater levels within 2 m of ground level. An attempt was made to improve on this broad-scale assessment in Oxford and to quantify risk rather than just susceptibility.…”

Improved understanding of spatio‐temporal controls on regional scale groundwater flooding using hydrograph analysis and impulse response functions

“…Regional groundwater flooding in the south of the UK in the winter of 2000/2001, and further major flooding in 2003 and 2007 that also included a significant groundwater component, led to legislation to assess and devise measures to address groundwater flood risk nationally. Work has been undertaken to develop national scale groundwater emergence and susceptibility maps (McKenzie, Rutter, & Hulbert, ; Morris, Cobby, & Parkes, ) that has led to the development of groundwater flood risk maps (ESI, ; JBA, ). These flood risk maps address the two main settings for groundwater flooding: shallow permeable superficial deposits (recent unconsolidated sediments overlying the bedrock) associated with large rivers; and unconfined bedrock aquifers.…”

The Handling of Hazard Data on a National Scale: A Case Study from the British Geological Survey

“…The methodology uses conceptual models for clear water and permeable superficial deposit flooding (McKenzie et al 2010). A set of rules is then developed within a GIS system consistent with each of these models and applied to a set of national spatial datasets that includes groundwater levels, DigMapGB, a derived river dataset, a digital terrain model (DTM) and permeability.…”