Spatial Variability and Drivers of Salt Marsh Cliff Erosion in the Dutch Wadden Sea: From Observation to Simulation

Lateral erosion of salt marshes via cliff retreat is a primary cause of global marsh loss, driven byinteractions between hydrodynamics, sediment, and vegetation. While previous studies show a linearrelationship between wave power and cliff retreat, models based on this relationship are largely unvalidated forshort‐term (sub‐yearly) and spatially variable predictions, limiting their practical application. This studyaddresses this gap by integrating a process‐based subgrid cliff erosion model into a 2DH hydrodynamic model,validated using high‐resolution UAV‐derived DEMs over 9 months in a Dutch Wadden Sea marsh. The sitefeatured 20–60 cm high cliffs retreating at ∼0.9 m/yr. Once calibrated, the model captured overall erosion trendsand volumes, confirming the linear wave power‐retreat relationship when averaged across the marsh. However,it did not account for local effects, like artificial structures, cliff undercutting, or mass failure, highlighting theneed for site‐specific calibration and better understanding of underlying processes. Simulations under varyinghydrodynamic conditions assessed marsh cliff vulnerability. Water levels determine the location and timing ofcliff exposure, while wave energy dictates retreat magnitude. Yearly storm surges caused the most significanterosion, whereas more extreme surges (5–10 years return‐period) submerged the marsh edge, limiting furthererosion. This research shows that the linear wave‐power relationship is scale‐dependent: it can be calibrated forlonger‐term, marsh‐averaged erosion volumes when sufficient local data support a linear relationship, but itsapplicability is limited for within‐marsh, shorter‐term forecasting. Accurate simulation and effective coastalmanagement require further understanding of the processes and implementation of non‐linear erosionmechanisms.