High-Frequency Tide-Surge-River Interaction in Estuaries: Causes and Implications for Coastal Flooding

Abstract

Tide-surge interaction creates perturbations to storm surge at tidal frequencies and can affect the timing and magnitude of surge in tidally energetic regions. To date, limited research has identified high-frequency tide-surge interaction (>4 cycles per day) in coastal areas, and its significance in fluvial estuaries (where we consider it tide-surge-river interaction) is not well documented. Water level and current velocity observations were used to analyze tide-surge-river interaction at multiple tidal and overtide frequencies inside of a shallow estuary. Near the head of the estuary, higher frequency harmonics dominate tide-surge-river interaction and produce amplitudes more than double that of wind and pressure-driven surge. Bottom friction enhanced by storm-induced currents is the primary mechanism behind the interaction, which is further amplified by within-estuary resonance. High-frequency tide-surge-river interactions in estuaries present a significant threat to human life, as the onset of flooding (in <1.5 hr) is more rapid than coastal storm surge flooding. Commonly used storm surge forecasting models neglect high-frequency tide-surge-river interaction and thus can markedly underestimate the magnitude and timing of inland storm surge flooding.