In the UK, there is a good understanding of the potential flood risk from rivers, the sea, surface water and reservoirs, with freely available flood hazard mapping. There is limited understanding about the risk for groundwater flooding however.
This has contributed to the under-recognition of groundwater flooding and limited management of the risk.
The primary aim of the groundwater modelling and mapping workstream is to develop approaches to model where groundwater levels could rise to be near the ground surface and how the water would then flow over the ground surface once it has emerged. The results have helped to develop our groundwater flood risk maps and trial groundwater flood warning service. They will also be used to inform groundwater management schemes and planning applications.
2024
Frequency analysis of groundwater levels across The Chalk of Project Groundwater
Frequency analysis of exceptionally high groundwater levels is not typically done, which means that we don’t understand the probability of flooding and the damage this can cause.
In 2024, we believe that, for the first time, we have estimated flood frequencies across a large area that can form the basis of groundwater hazard mapping. In particular, we have applied this estimation to both groundwater levels and emerging flows which maximises use of borehole and river gauge data to verify the results.
There remain a number of challenges to produce detailed maps, because of the way borehole data is collected, but we are continuing to explore whether this technique could be useful across other chalk areas.
Mapping the flood hazard from the highest recorded groundwater conditions
The Environment Agency's Modflow groundwater models are a cost effective and credible basis to predict the emergence of groundwater across large chalk areas.
This year, we took these outputs and began routing the flows across the ground surface everywhere in the Project Groundwater area. The Modflow models are not always calibrated for flood conditions however, which leaves gaps in our ability to model the different frequency events in some areas. We will work towards filling these gaps in 2025 – see below.
Investigating how the frequency and severity of groundwater flooding could change with climate
Through Project Groundwater-sponsored MSc research, we applied our frequency analysis and other techniques to predictions of future groundwater levels.
This provided insights into how wetter winters and drier summers could impact the likelihood and maximum levels that groundwater could reach towards the end of the century. Overall, the research suggested that groundwater levels in the boreholes studied are not projected to consistently increase or decrease over the next 60 years.
Despite this, the research indicated that there is still a constant risk of large fluctuations which could provide an increased risk of flooding or drought, with these risks varying across the Project Groundwater area.
2025
Collaborating with the Environment Agency to understand how Modflow models could better represent extremely high levels
The Environment Agency’s Modflow models are water resource groundwater models which we have shown also have real value in estimating emergence that leads to flooding.
In 2025, and as a strategic aim for the project, we will continue to work with the Environment Agency, exploring how having the same models that can represent droughts, floods and different management techniques could be a really powerful and holistic tool.
Learning from groundwater flooding in Hinksey Park to refine our approach to managing risk from the Permeable Superficial Deposits
Groundwater flooding from Permeable Superficial Deposits (PSD) shares many similarities with river flooding, including the mapping of its extents, depths, frequencies and timings.
New Hinksey, is one of the few communities with monitoring and hazard mapping of both groundwater and main rivers and with experience of managing both types of flooding.
Through reviewing people’s experience in New Hinskey, we will understand the value of treating groundwater separately, rather than as a new way of understanding the information already available for river flooding. This will inform how we should invest in groundwater flooding in other PSD communities.
Find out more about Project Groundwater
