Design challenges of multifunctional flood defences

Due to the changing climate and increasing urbanisation delta cities are faced with an increasing flood risk. In The Netherlands many of the flood defence infrastructures, such as dikes and flood walls, need to be adapted or improved in the near future, to comply to current or improved safety standards. These improvements directly affect landscape and urban development. In its 2008 report, the 2nd Delta Committee presented the idea of multifunctional flood defences, which are flood defence structures that deliberately provide opportunities for other functions. Since then, spatial designers and hydraulic engineers together delivered a wide palette of designs and concepts, resulting in a rather fluid and indefinable concept of multifunctional flood defences. This paper presents a method to describe the level of multifunctionality, based on two existing spatial and structural assessment methods from the fields of civil engineering and urban planning. The combined method distinguishes four ascending levels of integration, ranging from spatial optimisation to structural and functional integration. The combined classification method is tested on a selection of cases of multifunctional flood defences in the Netherlands. Based on this test, it is concluded that the classification method is a useful and generic method to describe the level of multifunctionality. Some of the selected examples look very innovative and multifunctional at first glance, while the level of spatial and structural integration is limited. Other examples might not be very spectacular from a spatial designers point of view, but show that true functional integration of flood protection with multiple other functions is already feasible, depending on the local context. The method helps to bridge the gap between the practices of civil engineering and urban and landscape design. Also, it makes clear that flood risk management is part of an overall process of integrated area development, anticipating on what could be described as a multifunctional flood defence zone.