Quantify the compound effects caused by the interactions between inland river system and coastal processes in hurricane coastal flooding through controlled hydrodynamic modeling experiments

Abstract

Coastal flooding during hurricanes is a complex phenomenon involving the interaction of multiple drivers operating across different spatial scales, such as storm surge, rainfall, river discharge, and tides. Accurately assessing and predicting compound flooding requires considering the cross-scale nature of these processes and their interdependencies. This study investigates the compound effects and cross-scale interactions of flood drivers during Hurricane Matthew (2016) along the South Carolina coast using a coupled hydrology-hydrodynamic model. The model domain encompasses the land-ocean continuum, from rivers to the coastal ocean, allowing for the examination of compound flooding across the entire system. Controlled numerical experiments are conducted to quantify the individual, combined, and compound impacts of flood drivers across scales by selectively including or excluding riverine, storm surge, and tidal forcings. The coupled modeling approach reveals distinct zones of positive and negative compound effects, depending on the alignment of coastal water levels with river flood timing. River-surge interactions alter flooding, causing increases upstream and decreases downstream compared to isolated effects. Tide-surge and tide-river interactions induce oscillatory compound effects. The study demonstrates that the compound effect significantly influences hurricane coastal flooding beyond the linear superposition of flooding caused by individual drivers. The cross-scale modeling framework and analysis approach presented here can inform multi-hazard analysis, coastal flood risk management, and future studies of complex, multi-scale hydrologic systems.