Has groundwater influenced the recent UK floods (December 2015 — January 2016)?

Rainfall amount per cent of 1981-2010 average

There is a more recent page about the groundwater levels as of 20th January 2016.

The festive season was marred by floods for many people in northern England (including Cumbria, Lancashire and Yorkshire) and Scotland (including Perthshire, Aberdeenshire and the Scottish Borders). The Met Office has released statistics for December showing that it was the wettest calendar month since records began in 1910.

In early 2014, many news stories about the flooding included a discussion of groundwater levels and the way rising levels in aquifers were causing and/or prolonging flooding in southern England and in the Thames valley. Groundwater has played a much smaller role in the recent flooding in Northern England and Scotland. Local geology explains much of the difference.

BGS has undertaken research on flooding over many years and has contributed to improving understanding of how, where and when flooding occurs. We have produced a range of datasets that have been developed to assist government agencies in planning for flood events and improving flood prevention.

Aquifer response to rainfall

Figure 1: Lancashire sandstone

Groundwater's influence on floods is greatest where there are fractured aquifers that are very responsive to rainfall events, such as chalk and limestone. Groundwater levels in these areas can rise several metres in a week in response to prolonged rainfall.

In northern England and Scotland, many catchments are dominated by impermeable rocks with very limited capacity to soak up rainfall, or by sandstone aquifers that respond much more slowly to rainfall. Groundwater levels in Lancashire rose just a few centimetres or tens of centimetres, as shown by the hydrograph for Yew Tree Farm (Figure 1).

Figure 2: Yorkshire chalk

Across the Pennines, more rapid rises in groundwater level have been observed in the Yorkshire chalk. The monitoring well at Wetwang rose by over 10 metres in response to the rainfall around Christmas 2015 (Figure 2), but levels in late autumn were relatively low in this aquifer. They haven't yet reached the heights seen during 2000–2001, where groundwater-driven flooding affected valleys in the Yorkshire Wolds and contributed to flooding on Humberside.

Even where groundwater doesn't directly contribute to a flood event it can be an important factor in the local dynamics of the flood event. Sands and gravels in river valleys absorb some of the rainfall and can reduce the intensity of a flood, but they can provide a pathway for water to flow below ground from a river to nearby properties, making flood defence harder, as well as prolonging the duration of the event.

BGS data, information and research into flooding

BGS have been working for many years to improve the understanding of flooding in order to provide data and knowledge that will help to reduce the impact of flooding on people in the UK and elsewhere in the world.

BGS works with partners to produce the monthly Hydrological Outlook UK report, which provides an insight into future hydrological conditions across the UK. Experts from the Met Office, the Centre for Ecology & Hydrology and BGS work together to assess the likely conditions over the following month and 3 month period. The outlook published in December 2015 is shown in Figure 3.

We also publish a monthly Hydrological Summary of the UK, which records the key meteorological and hydrological features (surface and groundwater) over the past month and considers the current status of water resources in the UK. This is also produced in partnership with the Centre for Ecology & Hydrology and the Met Office.

BGS has a range of datasets that have been developed to assist government agencies in planning for flood events and improving flood prevention. These are listed on our BGS flooding information page and include our susceptibility to groundwater flooding and BGS geological indicators of flooding datasets.

Our research into flooding includes aspects of groundwater flooding such as understanding groundwater flooding mechanisms, developing numerical and statistical models to allow prediction of groundwater level responses during flood events, and estimating the number of properties at risk from groundwater flooding.


Please contact Andrew McKenzie for further information.