Types of Flooding

To many people, a flood is a flood? However, there are different types of flooding events that can affect your property. It might even be the case that your home or building is being affected by more than one type of flood. Below, we explore the most common types of flooding that may affect your property.

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Surface flooding

In prolonged, exceptionally heavy downpours (that unfortunately are becoming more frequent), the ground may become saturated and the drains and sewers which carry away surface water may not be able to cope, leading to surface water flooding.

Although this is more likely in low-lying areas, and to premises at the foot of slopes, it can happen to many other properties which are not specifically designated as being at risk of flooding on the Environment Agency’s flood risk maps.

Surface water flooding may be triggered or made worse in urban areas where the ground consists of mostly hard surfaces such as concrete or tarmac, as the rainwater flows straight off, rather than soaking into the ground

Sewer flooding

When sewage escapes from the pipe through a manhole, drain, or by backing up through toilets, baths and sinks, this is known as sewer flooding.

Sewer flooding can be caused by a blockage in a sewer pipe or a failure of equipment when too much water enters the sewers from storm run-off (from roads and fields), rivers and watercourses which have overflowed. If the sewage enters a building, it is called ‘internal flooding’. If it floods gardens, or surrounding areas such as roads or public spaces, it is called ‘external flooding’.

Sewage flooding - types of flooding - PCA

Groundwater flooding - types of flooding - PCA

Groundwater flooding

Rising groundwater levels resulting from heavier rainfall and reduced water abstractions can present problems. Groundwater flooding generally occurs during long and intense rainfall when infiltration into the ground raises the level of the water table until it exceeds ground levels.

It is most common in low-lying areas, overlain by porous soils and rocks, or in areas with a naturally high water table.

River flooding

River flooding occurs when rivers and streams are unable to carry away floodwaters within their usual drainage channels. Adjacent low-lying properties and land are then liable to be flooded.

River flooding can cause widespread and extensive damage because of the sheer volume of water, and may be longer-lasting and more difficult to drain away. Fast-flowing floodwaters can also be a threat to peoples’ and animals’ safety and can structurally damage buildings.

River flooding - types of flooding - PCA

Coastal flooding - types of flooding - PCA

Coastal flooding

Coastal flooding is caused by high tides coinciding with a low-pressure storm system which raises sea and tidal water levels, overwhelming coastal defences. This may be made worse by gale force winds blowing the raised body of water onto the coast.

Coastal flooding may affect not only property on the coast itself, but also property in tidal river basins some distance from the coast, due to floodwater being forced up the tidal reaches of rivers and estuaries by raised sea levels and gales

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Types of Flooding