LONG-TERM DUNE EVOLUTION UNDER INTERACTING CROSS-SHORE AND LONGSHORE PROCESSES

Coastal dunes play an important role in flood protection and erosion mitigation along sandy coasts. Still, few models are available that predict long-term dune evolution. Dune processes are typically modeled at shorter time scales, focusing on storm impact. Meanwhile, long-term coastline evolution models typically ignore exchange of sediment between the beach and the dune. Instead, these models often consider a fixed profile that moves seaward or landward if gradients in the longshore transport are negative or positive, respectively. Nevertheless, it is evident from field studies and morphological models that longshore transport gradients provide a relevant contribution to both beach and dune evolution (Psuty, 1988), and that the dune and the beach respond to sediment budget changes at different time scales (Stive et al., 2002). As a step towards bridging the gap between nearshore, beach, and dune modelling, this study investigates the interaction between longshore transport gradients and the beach and dune evolution on decadal time scales. This aim is addressed by combining an analysis of a 22- year long data set at IJmuiden (The Netherlands; see Figure 1) with simulations using a semi-empirical crossshore model, the CS-model (Larson et al., 2016).