Forecasting coastal overtopping at engineered and naturally defended coastlines

Abstract As sea level rises and development of the coastal zone continues, flooding poses an increasing risk to communities. Wave runup can contribute many meters vertical reach sea, especially on steep gravel beaches, wave overtopping is a key contributor along coastlines exposed energetic conditions. However, operational forecasting has rarely been attempted due need for high-resolution inshore water levels conditions, up-to-date profile defence information, availability models or formulae that robustly predict range types. Here, we have developed tested efficient system providing warnings up three days in advance entire 1000 km coastline southwest England, called SWEEP-OWWL, which capable predicting elevation volumes macrotidal coastline, featuring embayed, sandy, gravel, engineered regions. Existing flood warning systems used process-based hydrodynamic model XBeach, but computational cost, resorted populating look-up tables using off-line simulations only single realisation bathymetry. Instead, SWEEP-OWWL runs ‘real-time’ computationally suite empirical shoaling, breaking, runup, equations at 184 profiles, forced with information from regional 1-km spectral model. Importantly, forecast be updated latest data no extra shown improve accuracy predicted rate by order magnitude some cases. Compared visual observations events live streaming webcams around southwest, correctly presence absence 97% showed skill differentiating between low high hazard events. Reliable forecasts could considerably enhance community's ability prepare mitigate against life, property, infrastructure during events, shows this achieved desktop PC regions both natural man-made defences.