Evaluating coastal multifunctionality: sand nourishment strategies at decadal timescales

Haye Hendrik Geukes , Tosca T. Kettler, Matthieu de Schipper, Peter van Bodegom, Alexander P.E. van Oudenhoven 

Globally, there is a growing societal need for multifunctional coastal climate adaptation of sandy shores in the coming decades. Sand nourishment strategies are increasingly regarded as promising nature-based approaches to adaptation. They may increase flood safety and mitigate coastal erosion while enhancing recreational and ecological functioning. However, their multifunctional potential has not yet been assessed under diverse climate impacts at decadal scales. This study analysed the effects of beach, shoreface and mega-nourishment strategies on the physical capacity of sandy shores to supply coastal multifunctionality, using a systems-based approach. Through a structured literature review, we identified eight indicators for recreational (2 indicators), ecological (3) and flood safety (3) functions. We integrated these indicators into a process-based sand distribution model for dissipative coastal profiles. We simulated indicator states as the coastal profile responded to the nourishment strategies under five sea-level rise scenarios and three erosion rates. Next, we calculated the extent to which the physical capacity for coastal functions and multifunctionality were supplied over six decades. Our results indicate that all three nourishment strategies can highly supply the capacity for coastal multifunctionality, although the drivers of this potential differed per strategy. These findings imply that sand nourishment strategies are viable approaches for multifunctional coastal climate adaptation in the coming decades. However, they require prioritising specific coastal features and functions. Although sand nourishment strategies remain high-impact interventions, they also allow for intentionally creating coastal landscapes. These landscapes may not only provide flood protection but also enhance the specific environmental and societal functions valued in dissipative sandy shores. Prioritising among these functions requires explicit political choices