1950
Research of Rijkswaterstaat in 1937 stated that the safety of the Dutch in periods of peak discharges and high water levels could not be assured. The closure of the large rivers and estuaries (Western and Eastern Scheldt, Haringvliet, Brouwershavense Gat) was thought to be the solution. In 1950 the damming of the Brielse Gat and Botlek was started and was the beginning of the Delta Works.

Oosterschelde barrier (Raimond Spekking)
The works were planned to be carried out gradually, but the 1953 flood showed that there was no time to waste. The Delta Works developments were accelerated.
Further reading
Deltawerken