The effects of tidal changes on nuisance flooding along the U.S. coastline

Abstract:

Nuisance flooding (NF) is defined as minor, nondestructive flooding that can still cause substantial negative socio-economic impacts to coastal communities. Sea level rise is a primary driver of an observed increase in NF events, but here we show that secular changes in tides often also contribute. These tidal changes may be caused by a deepening water column, naturally evolving coastal morphology, or by direct human influences (e.g. dams, landfill, dredging). An analysis of 40 tidal gauge records from U.S. coasts (exclusive of Alaska and Hawaii) finds that 18 locations experienced a 7-93% increase in NF events caused by tidal amplification, while decreases in tidal range suppressed NF frequency at 11 locations. The remaining 11 locations showed an insignificant influence from tidal trends, primarily at open coastal locations. Estuaries showed the largest changes ranging from -45% to +93%, and these can often be traced to anthropogenic alterations. The total number of NF days caused by tidal changes has increased at an exponential rate since 1950, adding ~27% to the total number of NF events observed in 2019. Here we also assess how much earlier (or later) critical thresholds of NF frequencies could be exceeded under sea-level rise due to the effects of tidal changes. We found that at 23 locations the 100 events/year threshold is exceeded earlier (between 1 and 47 years) due to tidal changes under the intermediate-low sea-level rise scenario, and at 11 locations it is exceeded later (between 1 and 8 years).