Weatherwatch: Groundwater flooding threatens thousands of homes

A man places sandbags outside a property close to the flooded main street in Old Malton, North Yorkshire. For people living on chalky soil proplonged rainfall is disastrous. Photograph: Anna Gowthorpe/PA

Chalky soil is so porous that a lot of rain soaks straight into it, reducing the chance of flooding and acting as a giant sponge. These aquifers feed the springs and provide the water supply for much of the south. But with recent rains even the biggest sponges get saturated.

Eight months ago, amid hosepipe bans, there were fears that it would take years of average rainfall before these depleted aquifers recovered. Then came the wettest three months the south had ever recorded. Normally in the summer, grass and trees soak up all the rain, but this year water levels began to rise.

Then with October and November's deluges these natural reservoirs began to fill faster. This is good news for nature, particularly the glorious but endangered chalk trout streams. Long dry springs high in the hills are beginning to flow again.

But for people living on chalk, prolonged rainfall can be disastrous. Groundwater flooding, literally water springing out of the ground and in some cases up through the floorboards, is potentially a threat to 380,000 properties in England and Wales. The problem can last for months.

In the Solent and South Downs area, the fastest to react to rising groundwater, alarms have been going off in boreholes in Hampshire and Sussex. The Environment Agency is warning householders to be prepared for flooding from beneath. Some residents of King's Somborne, on the banks of the river Test, have been told their cellars may begin to fill up this week.