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Shrinking and swelling of the ground (often reported as subsidence) is one of the most damaging geohazards in Britain today, costing the economy an estimated £3 billion over the past decade.

Many soils contain clay minerals that absorb water when wet (making them swell) and lose water as they dry (making them shrink). Many of us see this in our gardens when the ground becomes cracked during the summer, yet becomes ‘heavy’ in the winter. This ‘shrink–swell’ behaviour is controlled by the type and amount of clay in the soil and by seasonal changes, related to rainfall and local drainage, in the soil moisture content .

In this video we can see the effect of a clay swelling due to water ingress and the subsequent damage to the house above, known as ‘heave’. ���ճԹ� © ���ճԹ�.

Ground moisture variations may be related to a number of factors, including:

• weather variations
• vegetation, particularly growth or removal of trees
• human activity

Variation in ground moisture can cause ground movement, particularly in the upper two metres of the ground, which may affect building foundations, pipes or services.

The potential for shrink–swell to be a hazard has been assessed using 1:50 000-scale digital maps of superficial and bedrock deposits. These have been combined with information from the ���ճԹ� superficial thickness dataset, scientific and engineering reports. The detailed digital data illustrated in the map is available as attributed vector polygons, as raster grids and in spreadsheet format.

• property hazard information
• simplified data
• ground shrinkage and subsidence information