Adapting to climate change: the probabilistic versus the self-learning dike

Background

In the Netherlands the current dike design policy is to design flood defence structures corresponding to an agreed flooding probability with an extra safety board of at least 0.5 m. For river dikes a return period of 1250 years is used to determine the design water levels. A problem with this strategy is that it builds on assumptions with regard to the intrinsically uncertain probability distributions for the peak discharges. The uncertainty is considerable and due to (1) the measuring records that are limited to about 100 years and (2) the changing natural variability as a result of climate change. Although the probability distributions are regularly updated based on new discharge data the nature of the statistics is such that a change in the natural variability of the peak discharge affects the probability distribution only long after the actual change has happened. It is therefore inherent to this strategy that the actions taken to reduce the flood risk are not anticipatory but following. Therefore, we compare the performance of the probabilistic dike design strategy with the historic strategy, based on the concept of the ‘self-learning dike’. The basic principle of this strategy is that the dike is heightened immediately after the actual water level has exceeded the actual dike height minus a certain safety margin. This approach had two practical advantages: it does not depend on uncertain discharge statistics, and the rule of response is relatively simple. The two flood prevention strategies are compared on the basis of the flooding safety over a 100-year period. The Rhine gauge station at Lobith serves as case study. The research does not pertain to dike failure mechanisms other than overtopping or risk assessment in general. Nevertheless, dikes are still the primary flood defence mechanisms in many countries.

Objectives

The objective of this research is to compare the effectiveness of the probabilistic strategy dike design with the historic practice in the light of peak discharge uncertainty and climate change, and to determine under which conditions the historic practice of responding to peak water levels only can be sufficient.

Publications

Hoekstra, A.Y. (2005). Generalisme als specialisme: Waterbeheer in de context van duurzame ontwikkeling, globalisering, onzekerheden en risico's. Inaugural address, University of Twente, Enschede, The Netherlands.

De Kok, J.L and Hoekstra A.Y., Adapting to Climate Change: the self-learning dike, in: Tagungsband "Strategien und Instrumente zur Verbesserung des vorbeugenden Hochwasserschutzes" (Proc. "Strategies and Instruments for improvement of the existing Flood risk protection"), Institut für Wasserwirtschaft und Ökotechnologie, Magdeburg, November 23-25, Tangermünde, Germany.