Safety standards for the coastal dunes in The Netherlands

In 2014, the Dutch Delta Programme introduced new safety standards for the Dutch primary flood defence system that were derived using a risk-based approach. The Dutch primary flood defence system consists of a network of dykes (US: levees) and coastal dunes. The new safety standards take into account both the probability of inundation through flooding and the consequences of such a flood. The Dutch Delta Programme has derived the standards based on the risks for individual and group mortality (solidarity principle) and on a cost-benefit analysis (i.e. economic optimum). A full cost-benefit analysis is a data-intensive and a labour-intensive method, and therefore a simple, pragmatic approximation formula, referred to as the direct assessment approach, has been applied. The direct assessment approach yields a good estimate for economically optimal safety standards for dykes in the Netherlands. The direct assessment approach has subsequently been applied to the coastal dunes in the Netherlands. However, the correctness and applicability of this approximation to these locations has not been based upon hard empirical or analytical evidence. This paper shows that the direct assessment approach is indeed applicable to coastal dunes in the Netherlands but not as a direct consequence of its applicability to dykes but rather due to the specific nature of sand nourishments, which are used to reinforce the coastal dunes.