Over recent weeks, scientists from the Environment Agency (EA) and BGS have been keeping a close eye on groundwater levels, monitoring the response of aquifers to the heavy rainfall experienced in parts of the country in December 2015 and January 2016.
In the last week of January 2016 there was more rainfall in areas where groundwater levels were already high, but, although water levels rose, they did not generally reach the levels at which significant groundwater flooding may occur, and some levels are now declining. Groundwater flood alerts are still in place in areas of some southern counties of England, but the impact on properties and infrastructure has been limited.
Although the immediate risk of groundwater flooding is reducing, we remain in a situation where groundwater levels are relatively high and superficial aquifers (comprising relatively shallow, unconsolidated deposits) will be saturated. This means that further periods of intense or prolonged rainfall could potentially lead to more localised groundwater flooding.
The south east of England received up to >200 per cent of average January rainfall (Figure 1). Rainfall across the area from Eastbourne to Weymouth was mostly in the range of 150–200 mm (Figure 2).
The monitoring well at Chilgrove House is used to observe groundwater levels in the unconfined Chalk aquifer of West Sussex. Since the start of 2016, the groundwater level here rose to a peak of about 75.4 m, fell a few metres and then rose again in response to further rainfall (Figure 3). The water level in this well appears to be starting to fall again as of the morning of 3 February 2016.
The hydrograph for Ladies Mile near Patcham, East Sussex, is similar, although the EA state that "it is likely that groundwater levels in Patcham village will continue to rise until the weekend" (from the groundwater flooding in Patcham Flood Alert, updated on 2 February 2016).
You can read more about this aquifer in our report The Chalk aquifer of the South Downs.
The Yorkshire Chalk has seen below average rainfall in January (Figure 2). The groundwater level at Wetwang (in the unconfined Chalk) has responded to this and fallen by over 2.5 m since it peaked about 19 January 2016 (Figure 4). The less responsive confined Chalk is illustrated by Dalton Holme, where the groundwater level is still rising in response to the earlier rainfall (Figure 4).
You can download our report The Chalk Aquifer of Yorkshire for free.
Hydrograph data note: data up until the end of December 2015 are from the National Groundwater Level Archive (NGLA), and have been quality assured prior to submission, whereas January and February 2016 data are derived directly from the EA's telemetered boreholes and have not yet been quality assured.
Acknowledgement: the hydrographs include EA groundwater level data from the real time data API (Beta).
Please contact Andrew McKenzie for further information.