How can floods affect groundwater levels?

The Relationship between Groundwater and Flooding: Exploring the Link between Floods and Groundwater Levels in the UK

There are many places in the UK at high risk of flooding, with the Environment Agency stating that almost 5.9 million properties in England and Wales (one in six homes) constantly face the threat of rising water. 

This includes places such as Merseyside, Yorkshire, Cumbria, Somerset, Kent and Cornwall, with a combination of coastlines, floodplains and surface water flooding creating various issues. But do floods affect groundwater levels, and if so, how? We explain more below.

What is groundwater flooding?

Groundwater flooding occurs when water levels in rocks, underground soil or dormant springs (which is referred to as the water table) begin to rise. Should the water rise far enough to reach ground level it will become visible and could lead to homes and surrounding infrastructure being flooded. 

This is because the rising water can occur both externally and internally, coming up through floors or into basements and underground rooms. It usually occurs in regions with chalk bed rocks, or in river valleys that contain sand and gravel. 

Flooding in this way is a much slower process compared to other forms of water overflows, sometimes even taking place a number of months after heavy rainfall has occurred. Once started it can also last anywhere between a few days or a few months. 

How can floods affect groundwater levels?

Groundwater flooding levels change throughout the course of the year, generally rising higher during the winter months. Scientists have also noted in recent times that groundwater levels in Birmingham and London have been rising as water is no longer being pumped from wells as frequently as they once were at the start of the 20 century. 

A number of factors, including river water, rainfall, canal flows and irrigation return flow and floods, affect groundwater levels. When a nearby river floods the area, this will eventually be absorbed into the ground, further increasing groundwater levels. 

If the groundwater levels are already quite high, the combination of river water and rising underground water could increase the surface water level. This means even after the river flood has subsided the remaining groundwater could take much longer to dissipate. 

What can you do to stop groundwater floods?

Groundwater flooding is a natural event that is only visible to most people once the water reaches the surface. However, if you live in an area that frequently experiences high levels of rainfall, by investing in a stormwater tank you can reduce the risk of rising groundwater entering your property.

Stormwater tanks are designed to manage the infiltration of surface level water into nearby drainage systems using a flow-control chamber. They remain empty for long periods of time until heavy rainfall occurs, and as the tank starts to fill, water is slowly released out into nearby drainage flows.

Not only does this make it safer for your property, but it ensures your garden and land does not become waterlogged and by releasing into nearby drains, while also reducing the risk of local flooding.