Increased Groundwater Flood Risk in England

By Jon Haycox: 18 February 2021

As of February 2021, groundwater levels are now high in many areas of England with properties on alert in Kent, Surrey, Berkshire, Hampshire and Wiltshire for the risk of groundwater flooding. GeoSmart Information are specialists in groundwater and are monitoring this developing situation. Above average rainfall has fallen in many areas in October and December, with January having very high rainfall due to Storm Christoph. The combination of heavy rain and already exceptionally high groundwater levels led to increased runoff contributing to river flooding, and surface water flooding.

Rainfall anomaly charts for October 2020 (left) to January 2021 (right). Darkest blue shading for areas receiving twice the amount of rainfall than the period 1981-2010.

Groundwater levels in Kent have been a concern since December. The rainfall from Storm Christoph has led to levels rising further with properties in and around the Nailbourne Valley, Alkham and Petham in East Kent receiving an alert for possible flooding from groundwater.

A Groundwater Flood Alert was issued by the EA for Preston Candover and Old Alresford in Hampshire on 11^th January 2021 and this remains in place. Rising groundwater levels has caused cellar flooding in Preston Candover village and groundwater may prevent septic tanks from operating effectively in Old Alresford. This area is now included in the Flood Guidance Statement from the Flood Forecast Centre with localised groundwater flooding impacts affecting a few properties highlighted as a specific area of concern from Friday 19 February onwards. West Sussex and Brighton are also noted as areas where groundwater flooding may occur from Friday.

Groundwater contributed to the flooding in Malton in Yorkshire at the end of January. Although the immediate risk of flooding following the heavy rain of Storm Christoph receded, groundwater levels remain high which caused localised risk of flooding to remain days after particularly for properties in Old Malton. Pumps are in operation in the area to manage groundwater and surface water. Groundwater in this area emerges from springs occurring at the contact between the Corallian Limestone and the low permeability mudstone.

In the East of England, groundwater levels are also high. In Bury St Edmunds, the areas Eastgate Street, Barn Lane and parts of Vinefields are susceptible to groundwater flooding if groundwater levels increase over the next few weeks. Areas of Newmarket are also on alert, including the High Street. On the edge of London both Egham and Maidenhead also have groundwater flood alerts in place.

In the South West of England, groundwater flood alerts now cover the Cranborne Chase, Salisbury Plain and West of Dorset areas. Flooding to minor roads could be a problem in these locations and a combination of flood water and icy conditions will make roads treacherous. EA are advising that pumping equipment and property level protection measures should be set out where available.

GeoSmart’s Groundwater Flood Forecast Service. Red markers indicate a borehole exceeding or forecast to exceed flood threshold within 5 days. Yellow shading is EA groundwater flood alert areas.

Groundwater flooding represents a significant part of the overall flood risk in the UK and last year was a near-miss in terms of a national groundwater flood event. The UK’s climate is changing, and this will potentially increase the frequency, severity and extent of groundwater flooding. Businesses and individuals should take action to assess vulnerability and improve resilience if they are at risk to groundwater flooding and climate change. The first step in this process is to establish the current risk of groundwater flooding and how this might change in the future, such as by using a groundwater flood risk map to identify areas at risk of groundwater flooding.

The GeoSmart Groundwater Forecast is the UK’s first early warning system on groundwater flooding for property, infrastructure and public service providers. Up to 30-days advanced warning of groundwater flood risks enables smarter resilience planning and the forecast provides critical answers on when and how long flooding could occur. Service users are provided with real-time data on which to make informed decisions and assess the likely future risk to their assets. The forecast can be used in combination with the GeoSmart GW5 groundwater flood risk map to find the areas which are most susceptible.

Geosmart’s groundwater flood forecasting system predicted groundwater levels at an indicator borehole for Nailbourne in East Kent issued on 26th January, predicting groundwater levels to rise above the threshold. A groundwater flood alert was issued for the area by the Environment Agency on 2nd February.

GeoSmart’s Flood Forecasting uses a network of boreholes across the country and monitors infiltration history and the latest rainfall forecasts to predict where groundwater levels will be dangerously high, such as this borehole at Little Bucket Farm in East Kent. The system can accurately predict the changes in water levels days to weeks to months in advance.

Groundwater levels are currently high and rising in many areas of the country. As of 16^th February, twenty boreholes in our system are at or near their thresholds. Based on the rainfall forecast, the levels look like they will peak this week at most sites but more rainfall later in February may change this.

Tags: flood risk, Flooding, Groundwater, groundwater risk