Nature-based sandy interventions:finding synergies between flood safety, beach recreation and nature

Socio-economic pressures in coastal zones are rising worldwide, leaving increasingly less room for natural coastal dynamics. Identifying synergies between social and natural systems seems crucial for fostering sustainable coexistence and co-development. Recent multi-functional, nature-based interventions on the Dutch coast offer great potential in that respect. Constructed by mega-nourishment, these interventions aim at improving flood safety on a decadal scale by increased dune growth, while enhancing ecological and recreational value. Surprisingly, studies evaluating these innovative solutions paid little attention to how the social and natural systems interact in these human-made coastal landscapes (which we refer to as sandy anthropogenic shores, or SAS). We do not know whether these interactions strengthen or weaken the primary safety function of the nature-based interventions throughout its lifetime.Using the Hondsbossche Dunes and the Sand Motor SAS as Living Labs, we investigated how recreation, embryo dunes and flood safety co-evolve over time and across space. Based on field studies and a participatory modelling process we have integrated beach visitors’ behaviour with novel biomorphological models to evaluate the evolving functionality of the interventions.Simulations over 20–50 years showed that on wide, elevated SAS beaches, high recreation pressure constrained embryo dune formation, allowing for continued growth of the original foredune thus enhancing long-term flood safety. However, this synergy between recreation and flood safety came at the cost of ecological value. Further exploration of SAS design and recreation scenarios could reveal whether ways exist to achieve synergies among all three functions: recreation, flood safety, and ecological value.