How tidal properties influence the future duration of coastal flooding

In this manuscript, we explore how tidal properties influence the duration of coastal flooding, and therefore impact. We find analytically that 4 factors impact the duration of the high-water stand: the dominant tide-wave period, the maximum water-level above a datum, the tidal amplitude, and the interaction of diurnal and semidiurnal tidal amplitudes and phases. Some regions—such as the US Gulf Coast—have a combination of tidal properties that leads to long flood durations (>20 hours) for modest inundation depths (e.g., 0.2m). Regions with large semidiurnal tides (such as Gulf of Maine) are inundated for only 1-2 hours, for the same depth of flooding. Within individual estuaries, the potential duration of a 0.2m minor flood event varies by a factor of more than two (e.g., San Francisco Bay, Chesapeake Bay). Combined with relative sea-level rise (RSLR) rates that vary from less than 0 mm/yr to 10 mm/yr around North America, the observed timescale to transition from a zero to two hour flood length varies from 1-87 years. This large spatial variability in tidal inundation properties has implications for hazard planning, ecological adaptation and the future evolution of coastal flood events.