This prompted a major research programme, which produced the following astonishing results: water sinks into the soil under trees at 67 times the rate at which it sinks into the soil under grass. The roots of the trees provide channels down which the water flows, deep into the ground. The soil there becomes a sponge, a reservoir which sucks up water and then releases it slowly. In the pastures, by contrast, the small sharp hooves of the sheep puddle the ground, making it almost impermeable, a hard pan off which the rain gushes.
Many years ago, river managers believed that the best way to prevent floods was to straighten, canalise and dredge rivers along much of their length, to enhance their capacity for carrying water. They soon discovered that this was not just wrong but also counterproductive. A river can, at any moment, carry very little of the water that falls on its catchment: the great majority must be stored in the soils and on the floodplains.
Since 2007, there has been a review, a parliamentary inquiry, two bills, new flood management programmes, but next to nothing has changed. Floods, because of the way we manage our land and rivers, remain inevitable. We pay a fortune in farm subsidies and river-mangling projects to have our towns flooded and homes and lives wrecked.