Adaptation of the Hollandsche IJssel storm surge barrier

Abstract

The storm surge barrier and levees located in the Hollandsche IJssel do not fulfill the current safety standards according to the third nationwide safety assessment. The non-closure probability of the storm surge barrier is too high and the inner slope stability of the levees is too low. Besides the problems regarding the flooding safety also problems concerning salt intrusion into the Hollandsche IJssel, sea level rise that might occur, tidal ecology in the river and local developments in the surrounding play an important role. The objective of this thesis is the development and conceptual design of a solution for the important problems in the Hollandsche IJssel. The solution needs to be cost-effective and consists of a technically and societal feasible design. After analysis of different solutions, adaptation of the Hollandsche IJssel storm surge barrier is preferred because the investments needed to adapt the storm surge barrier are much lower than the construction of a dam or new storm surge barrier. The total solution adapts the Hollandsche IJssel storm surge barrier, changes the current closure scheme of the barrier and postpones the construction of a new structure that eventually will be needed. The adapted storm surge barrier has a lower closure level to decrease the governing water levels on the Hollandsche IJssel and therefore decreases the risk of flooding and the investments needed for the reinforcement of the levees. The non-closure probability of the storm surge barrier should decrease to limit the effect of the non-closure probability on the governing water levels. When the storm surge barrier does not close high water levels will be introduced on the Hollandsche IJssel, the effect of the non-closure probability should account for this high water levels. The storm surge barrier will also close during low discharges to prevent salt intrusion and consequently the stop of the fresh water inlet near Gouda. The inlet near Gouda uses fresh water to flush the canal system of Central Holland and prevents damage to agriculture. Due to the lower closure level and use of the storm surge barrier during salt intrusion governing loads on the storm surge barrier increase. The existing steel gate that closes the Hollandsche IJssel storm surge barrier needs to be adapted to withstand the increases loads. Steel plates need to be welded to increase the capacity of critical steel elements within the storm surge barrier. The effect of the adaptations is that a small part of the investments needed for the levee reinforcement is prevented and that the risks of flooding in dike ring 14 and 15 decrease. It is assumed that it is possible to decrease the non-closure probability and therefore reduce the effect of the governing water levels. The recommendations at the end of this study focus on the research that is needed into the exact effect and design of the adaptations.