Understanding the Different Types of Flooding…
…and How They Affect Buildings
Understanding the different types of flooding and how they affect buildings is essential for property owners, estate managers, and developers alike. From surface water and groundwater to river and coastal flooding, each presents unique risks to a building’s structure, durability, and long-term condition. Recognising these distinctions is key to assessing risk and planning appropriate mitigation or resilience measures.
How Flooding Affects Buildings
The impact of flooding on buildings varies significantly depending on the nature of the flood. Surface water flooding can cause rapid inundation at ground level, often damaging internal finishes, electrical systems, and ground floor furnishings. Groundwater flooding, by contrast, can seep slowly through floors and foundations, leading to prolonged damp conditions, structural weakening, and hidden mould growth. River and coastal flooding tend to exert greater hydraulic pressure on walls and substructures, sometimes undermining foundations or breaching structural integrity, especially in older buildings. Saltwater from coastal flooding is particularly corrosive, posing long-term risks to materials such as brickwork, metal fixings, and concrete. In cases of compound flooding, the effects can be compounded—literally—with water ingress occurring from multiple directions and drainage systems overwhelmed, making recovery and repair more complex.
Surface Water (Pluvial) Flooding
This type of flooding occurs when rainfall is so intense that the drainage systems—whether natural or man-made—cannot cope. It can happen during any heavy downpour and is particularly difficult to predict, unlike river or coastal flooding. Because it depends on the volume and distribution of rainfall in a short time frame, surface water flooding can affect properties with little or no warning, even if they are located far from rivers or coastlines.
Groundwater Flooding
Groundwater flooding happens when the water table rises and emerges above ground level. This can lead to water entering buildings through floors and foundations. Unlike other types of flooding, it tends to occur gradually following prolonged or repeated periods of heavy rainfall and may persist for weeks or even months. Properties with basements or located in areas with high water tables are especially vulnerable.
River (Fluvial) Flooding
Fluvial flooding is typically caused by sustained rainfall resulting in river levels rising and overtopping their banks. The risk is closely linked to the river’s capacity and the presence (or absence) of natural flood plains. Urban development and changes to land use can inadvertently displace floodwaters further downstream, potentially affecting areas that have not historically flooded.
Coastal Flooding
Coastal flooding usually results from a combination of high tides, strong winds, and low atmospheric pressure systems, which can create storm surges. These events can cause extreme forces to be exerted on buildings in exposed coastal locations. The combination of wave action and saltwater inundation can cause both structural and environmental damage.
Compound Flooding
This occurs when two or more types of flooding coincide, such as high river levels combining with coastal surges. Compound events can increase the severity and complexity of a flood, often overwhelming defences that would otherwise cope with a single source.
Understanding Flood Risk
Understanding the types of flooding and how they affect buildings is not just useful for property professionals—it’s vital for anyone planning repairs, insurance assessments, or long-term resilience strategies.
To assess the likelihood of flooding in your area or at a specific property, you can refer to the Government’s Flood Map for Planning. This tool provides a useful starting point for evaluating potential risk from rivers, seas, and surface water.
For practical advice on what to do if flooding does occur, including immediate steps to protect your home and how to deal with flood damage, read our related article: How to Cope During a Flood.
