The Delta Plan
A disaster such as the Flood of 1953 clearly should never be allowed to happen again, everyone was in agreement on that. The specially established Delta Commission came up with a plan that very year. In addition to reinforcing the sea walls, the Commission advised to reduce the coastline by some 700 kilometers, taking the premise that the less coastline there was, the easier it would be to defend.
The Delta Commission proposed blocking the estuaries in the delta completely and raising all sea walls to the so-called "delta level", for which their starting point was a level of five metres above NAP (Normal Amsterdam Level) at the Hook of Holland. This would reduce the risk of flooding to 1/4000 per annum for the delta area and to 1/10 000 per annum for the conurbation of Western Holland.
Only the Nieuwe Waterweg and the Westerschelde would remain open to shipping given the economic interests of the ports of Rotterdam and Antwerp. The dykes along these estuaries would thus have to be raised to the delta level.
The Delta Law
The Delta law, which resulted from the Commission's plans, was passed by Parliament in 1957. The Delta plan was to provide other benefits in addition to added security: improved water control in a large part of the country, less land becoming brackish, the establishment of freshwater basins to supply agriculture, new areas for recreation and - across the dams - better connections in the Southwest of the Netherlands.
A department called the Deltadienst was established on May 1,1958. It fell under the direct domain of the central management of the Ministry of Transport and Public Works (Rijkswaterstaat). During the years, it grew to be one of the largest and most complex departments ever to have functioned within Rijkswaterstaat. The Deltadienst had to translate the general principles of the Delta Act into technical tours de force. Above all, the plans had to be continuously adapted to the changing factors in hydraulic engineering, soil science, politics and finance.
The greatest part of the Delta works in the south-west Netherlands has been carried out by the Deltadienst in collaboration with many, many contractors. For years, tens of thousands of people found employment with the Delta works.
The Delta Project was an enormous undertaking for Dutch hydraulic engineers. No other country in the world had ever dammed off such deep, broad tidal inlets. Past experience and existing techniques were inadequate to deal with these huge projects.
The difference between high and low tide in the Delta is about three metres. Twice a day, the water flows in and out of the estuaries. The currents are strong and huge amounts of sand are shifted about.
The engineers had to deal with unfavourable weather conditions that created powerful waves in the estuaries.
From small to big
One thing was clear: new techniques would have to be developed in full speed. Hydraulic engineers resolved to build from small to big, from easy to difficult. This way the work itself would be a learning experience: new technical possibilities could be tried out and developed during implementation of the Delta Project.
Thus, prefabrication came in use and new specialized machines were developed. In 1961, sluice caissons appeared alongside the normal caissons and the cableway with gondolas was designed to dam the huge closing gaps. The house-high concrete caissons were improved and the use of synthetics was introduced at the beginning of the 1970s. Synthetic materials were used to protect the bottom and as dike linings.
Hydrodynamic studies became more and more refined through lab research, use of the computer slowly but surely became well-established, and measurement techniques and weather forecasts became more and more precise.