Rising damp

I work on farms in the fens of East Anglia, UK, where the water table is quite high. Even when there has been no rain, the fields seem dry when tides at the coast are low, yet at high tides, the water seems to rise and make the fields wet. We all know that the moon affects tides at sea, but can it also affect the height of the water table quite far inland?

• The moon’s gravity creates a tidal bulge on Earth, both at the point closest to the moon and the point furthest away. This bulge occurs in both water and solid rock, although because the rock resists deformation, the effect is more obvious for the sea than the land. The movement of water in the water table will be somewhere in between these two, because its flow is impeded by the soil.

The height of the water table will rise anywhere, independent of the distance inland. But close to the sea, the tides coming up the rivers will slow the flow of water from the land into those rivers, with this effect extending as far as the river is tidal.

Land “tides”, although too small to be easily visible, caused a distortion in CERN’s Large Electron-Positron Collider, producing an effect on the ring energy that had to be allowed for in some of the measurements.

Paul Kyberd, Uxbridge, Middlesex, UK

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