Afsluitdijk upgrading, non typical Dutch solutions

Abstract

The Afsluitdijk (Enclosure Dam) is a major causeway in the Netherlands, which was constructed between 1927 and 1933, running from Den Oever on Wieringen in North Holland province, to the village of Zurich in Friesland province. The dam is 32 kilometers long and 90 m wide, with an initial height of 7.25 m above sea-level and a slope of 1:4 (original slope, now 1:3.6) on each side (Rijkswaterstaat, 2009). After 80 years of successful performance, expected changes in boundary conditions and an increase of safety requirements make necessary to think of an adaptation of the structure, so it can perform its function in the future. Rijkswaterstaat has decided to adopt an overtopping resistant solution which provides the required protection until the year 2050. This project is aiming to define and propose a new non-typical Dutch dike configuration which needs to comply with Employer’s Requirements. As a starting point, an existing cross section from the Afsluitdijk is used. Mean Waddenzee bottom elevation at the Afsluitdijk is between -4.0m to -5.0m, NAP referred. For every possible new configuration, -5.0m is adopted trying to perform a representative design. In the intermediate design, several non-typical Dutch solutions have been defined trying to cover a wide range of options. Twelve feasible alternatives have been evaluated during the Intermediate Design. Then, a comparison among them is done by means of a multi-criteria analysis, together with cost estimations. As a result, the two more favourable alternatives, design 4 and design 10, were selected. In the final stage, further studies were done for both selected alternatives, which were contrasted with Rijkswaterstaat adopted solution (OverTopping resistant solution). Design 10 is the most advantageous of the proposed solutions. However, current politics dominant way of thinking is directly influencing Rijkswaterstaat standards and procedures. Consequently, possible solutions should be the less expensive ones. As a major conclusion, this report is proposing Rijkswaterstaat to think over the whole life cycle of the structures. This could lead to introduce more flexibility and adaptability into the designs (robust designs including future planned adaptation). Finally, is up to the Ministry of Infrastructure and the Environment to decide whether providing advantages to future generations is worth a larger investment.