Coastal water levels during storms result from interacting tides, storm surges, waves, currents, bathymetry, and coastal geometry, producing spatially heterogeneous responses that remain difficult to characterize from point observations alone. The Surface Water and Ocean Topography (SWOT) mission provides a new opportunity to investigate this complexity through wide-swath High-Resolution (HR) observations of sea surface height (SSH). Here, SWOT HR water levels are first evaluated against five tide gauges in the English Channel and subsequently analyzed at three contrasting sites, Cherbourg, Villers-sur-Mer, and Étretat, using complementary spatial and scale-resolved approaches. SWOT HR shows strong agreement with tide gauges at the best-performing sites, with RMSE values of approximately 0.11 m and correlations exceeding 0.99, while accuracy remains site dependent. Beyond point-based validation, the two-dimensional HR fields reveal pronounced spatial heterogeneity, including localized and elongated SSH anomalies with distinct geometries and orientations. EOF decomposition shows that more than half of the variance remains beyond the first six modes at all three sites, highlighting the complexity of the HR spatial signal. These residual structures are spatially organized rather than random, while their point-by-point relationship with radar backscatter (σ⁰) remains negligible. Two-dimensional Morlet wavelet analysis identifies a recurrent energetic range of approximately 0.5–1.0 km across the three domains, showing strongly contrasting intensity, localization, geometry, and persistence across neighboring scales. Comparison with independent wave, surface-current, and bathymetric fields further shows that this variability occurs within markedly different hydrodynamic and morphological environments, consistent with the combined influence of storm forcing and local coastal configuration rather than a single controlling process. The complementarity of these analyses demonstrates the added value of SWOT HR for resolving the two-dimensional, multiscale complexity of storm-time coastal SSH, providing new spatial information for understanding coastal dynamics and for high-resolution model validation and data assimilation.

Coastal water levels during storms result from interacting tides, storm surges, waves, currents, bathymetry, and coastal geometry, producing spatially heterogeneous responses that remain difficult to characterize from point observations alone. The Surface Water and Ocean Topography (SWOT) mission provides a new opportunity to investigate this complexity through wide-swath High-Resolution (HR) observations of sea surface height (SSH). Here, SWOT HR water levels are first evaluated against five tide gauges in the English Channel and subsequently analyzed at three contrasting sites, Cherbourg, Villers-sur-Mer, and Étretat, using complementary spatial and scale-resolved approaches. SWOT HR shows strong agreement with tide gauges at the best-performing sites, with RMSE values of approximately 0.11 m and correlations exceeding 0.99, while accuracy remains site-dependent. Beyond point-based validation, the two-dimensional HR fields reveal pronounced spatial heterogeneity, including localized and elongated SSH anomalies with distinct geometries and orientations. EOF decomposition shows that more than half of the variance remains beyond the first six modes at all three sites, highlighting the complexity of the HR spatial signal. The detrended SSH anomalies show organized spatial patterns, while their point-by-point linear correlations with radar backscatter (σ⁰) remain close to zero. Across the three investigated coastal domains and two storm events, the two-dimensional wavelet analysis identifies enhanced SSH variability within an energetic scale range of approximately 0.5–1.0 km, although its intensity, spatial distribution, and organization differ substantially among sites. Comparison with independent wave, surface-current, and bathymetric fields further places these observations within contrasting hydrodynamic and morphological environments, suggesting that the observed sub-kilometer SSH variability may be associated with local coastal processes, although their individual contributions remain unresolved. . Together, these analyses demonstrate the added value of SWOT HR for resolving the two-dimensional, multiscale complexity of storm-time coastal SSH, providing new spatial information for investigating coastal dynamics and supporting high-resolution model validation and data assimilation.

A real-scale OpenFOAM-based numerical framework is assessed for simulating storm-induced wave run-up on a natural macrotidal beach, benchmarking it against the non-hydrostatic phase-resolving model SWASH and field measurements. The simulations were carried out on a cross-shore transect of Villers-sur-Mer, a macrotidal sandy beach on the Normandy coast of France, under conditions representative of Storm Ciara in the English Channel during February 2020. A numerical wave flume was built with OpenFOAM and the waves2Foam library to reproduce wave propagation, breaking, and swash over the natural bathymetry, from which the extreme run-up (R2%) was extracted. Three sea states were simulated, spanning a range of significant wave heights, peak periods, and water levels, with each case validated independently against timestack-derived field measurements and SWASH predictions. The two high-water cases yielded R2% = 1.68 and 1.59 m with OpenFOAM, in close agreement with the field estimates (1.66 and 1.59m) and the SWASH values (1.66 and 1.56m), with relative errors below 1%. The dissipative low-water case yielded 0.87 m against a field value of 0.91 m (SWASH: 0.88 m), a relative error of approximately 4.4%. Across all three sea states, the predicted run-up showed a physically consistent response to incident wave height, period, and water level. Beyond these exceedance statistics, the two-phase formulation resolves the detailed surf- and swash-zone hydrodynamics, providing physical information inaccessible to depth-integrated models. These results show that OpenFOAM reliably reproduces storm-induced run-up on natural macrotidal beaches and offers a high-fidelity complement to efficient phase-resolving models for coastal flooding.

Coastal regions are increasingly at risk of flooding and erosion from sea-level rise, extreme storm events, and anthropogenic activities. Wave runup, which can contribute over 50% to extreme total water levels at the shoreline, is a critical driver of both flooding and morphological change. Consequently, accurate prediction of wave runup is essential for assessing coastal risk and enhancing the resilience of coastal infrastructure, especially during high tides and storm events. However, directly measuring wave runup under storm conditions is challenging due to its highly dynamic nature. To address this, shore-based video systems provide a practical, non-intrusive solution for continuous, wide-view monitoring of shoreline movement.This research focuses on storm-induced wave runup along the dissipative, gently sloping beach of Villers-sur-Mer in northwest France, integrating a phase-resolving numerical model (SWASH) with high-resolution shore-based video observations. The study assesses the contributions of infragravity waves and sea-swell components to shoreline excursions and total water levels during energetic conditions, providing critical insights for flood risk assessments and coastal resilience strategies. Villers-sur-Mer is characterized by a macrotidal, highly dissipative system, notable for its complex nearshore bathymetry, strong wave-tide interactions, a gentle intertidal slope (~1%), and a substantial tidal range (approximately 3–10 m). Since 2019, a video monitoring system has been collecting 10-minute timestacks at a frequency of 2 Hz, capturing shoreline position and runup variability, providing a robust dataset for model validation under macrotidal conditions. The SWASH model was configured in two-dimensional, non-hydrostatic mode at high spatial resolution, using an October 2019 LiDAR-derived topo-bathymetric surface, forced with conditions from Storm Ciara (February 2020), one of the most energetic storms to impact the French coastline.Model results show spatial variability in water levels, with relatively weak offshore gradients that intensify toward the inner surf zone where bathymetric slopes and curvature are greater. Along the representative transect, the wave energy spectra reveal a persistent sea–swell peak that diminishes shoreward, reflecting the strong dissipation characteristics of the surf zone. The video timestacks show quasi-periodic shoreline excursions, indicative of low-frequency modulation of runup during energetic conditions; runup maxima align with the arrival of distinct swash fronts. More gently sloping, highly dissipative sections display predominantly infragravity-driven shoreline motion, with smaller excursion amplitudes under comparable offshore forcing.Overall, the integrated framework provides process-based insights into storm-driven runup on macrotidal, dissipative coasts, supporting improved site-specific hazard mapping, flood risk assessment, and early-warning applications. By resolving the joint roles of infragravity and sea–swell motions in controlling runup and shoreline excursions during severe storms, the study advances process-informed coastal resilience planning and design for dissipative beach environments.