The disastrous stormflood of 1953 has caused in the Netherlands an intensive research on the mechanism of damages of sea-walls and on the problem of safety. It was rather quickly understood that the damages of the sea-walls must have been caused by overflowing water only. The overtopping water, flowing down along the inner slope, penetrated into this slope. The resulting groundwater flow in the section of-the bank-body just beneath*"this slope must have reduced the friction resistance of the soil, m consequence of which slides occurred in the inner slopes, in many cases resulting m a total destruction of the bank-body. Obviously there was something wrong with our sea-walls, but at first it was not very clear in which way they had to be improved, rfe could distinguish two different ways, two different principles. Either vie should design our sea-walls so high, that overtopping would never occur, or we should construct a bank-body, that would be wholly proof against the action of overflowing water.