Research & Projects

In 2017 Mark Voorendt has finished his PhD-research on multifunctional flood defences. The result of the research, his doctoral dissertation, can be found here.

Increased need for space in urban areas has recently led to more attention for combining functions in flood defences. A flood defence with additional functions is referred to as a multifunctional flood defence. In Zwijndrecht, for example, a quay has been combined with a subsoil parking garage, leaving space for a pedestrian area along the Merwede river. Also the improvement of dikes in order to reduce increased flood risk, requires a multifunctional approach if houses or other buildings are situated in or along these flood defences.

There are, however, some serious concerns regards multifunctional flood defences. Governance issues are very delicate because of possible conflicts in responsibilities. Who, for example, is responsible for the flooding of a large area in case of the collapse of a parking garage that is part of a primary flood defence? The owner of the garage will probably feel responsible to have his damage repaired or refunded, but he most likely will not feel accountable for the flooding of half a province. So, governance aspects should be arranged in advance.

An interesting aspect relevant for this research comes from urban planning concepts, namely the distinction of spatial dimensions of multifunctionality. This gives an indication of the degree of integration of the various functions. This ranges from shared use, where the flood defence structure is used by another function, to full integration where multiple spatial elements are making use of the same structure. In this sense, multi-structurality seems to be more relevant than multifunctionality.

Irrespective of the degree of integration, it should be ascertained that a combined (multifunctional) flood defence meets the requirements regards safety. The safety depends on the structural quality of the flood defence and the structural assessment of multifunctional flood defences is the topic of the present research. The objective of this research is to quantify the effects of the structural parts of a multifunctional flood defence on the strength and stability of the overall structure, for the benefit of the structural assessment of these defences. 'Assessment' here applies to both the design of new flood defences and the check of existing structures.

Technical aspects relevant for the structural assessment of multifunctional flood defences consist of the acting loads (water, wind, soil, etc.), the resistance against loads (material properties, and bearing capacity of the subsoil), the required safety level (the margin between loads and resistance) and future developments that could influence the safety (adaptability and possibilities of inspection and maintenance). Furthermore, the construction phase should always be integral part of the design of hydraulic structures, so constructability is mentioned as a separate aspect. Regards the life cycle principle it is good to anticipate possibilities of re-use and demolishing during the design. Multi-structurality goes accompanied with some extra assessment aspects: the mutual influence of the structural parts on their strength and stability (extra loads) and the interface between the structural parts (friction, cohesion, adhesion). Designing a framework to assess the aforementioned aspects is considered the main task for the present research.

The project was part of a programme 'sustainable and integral design of multifunctional flood defences', which was partly funded by the STW foundation. In total, twelve projects have been defined within this programme, covering urban planning, landscape architecture, finance, governance, adaptability and technical aspects.


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