The first problem with designing this dam was the waters of the great rivers, the Maas and the Rijn. The overflow of these rivers ends in the Haringvliet and if there was a dam this water could flood the land the dam should protect. They had to design an ‘open’ dam. They decided to make locks in the dam so the water of the Maas and the Rijn could be drained off when needed. Officially these constructions were no locks to let ships pass through but sluices for discharging water.