During a hydrological-meteorological investigation at a former beachplain at the Dutch island of Schiermonnikoog, groundwater fluctuations were recorded. Except for daily changes of the groundwater level there appeared to be exceptionally high fluctuations during rainfall. This phenomenon can be explained by the so-called »lisse-effect«.
This implies that the phreatic level can rise rapidly due to an increased pressure of the soilair above the capillary fringe. The increase of the pressure is caused here by the capillary infiltration of rainwater in the soil
At Schiermonnikoog it became obvious that the depth of infiltration and the extent of groundwater rise were determined by the thickness of a semipervious layer at the surface with strong capillary tension.