Are Extreme Skew Surges Independent of High Water Levels in a Mixed Semidiurnal Tidal Regime?

Abstract

Based on previous studies of tide-gauge records from locations with semidiurnal tidal regimes, extreme skew surges are always assumed independent of the high water (HW). However, differences in water depth between HW peaks of semidiurnal tidal regimes can be much lower than those in mixed semidiurnal regimes, where one daily HW is higher than the other. We statistically analyze tide-gauge records of 15 sites worldwide with a mixed semidiurnal regime and find that for approximately half of these sites extreme skew surges occur more often during smaller HWs. This dependence is not caused by seasonality effects, and the places that show dependence are all located in areas with a shallow continental shelf, thus indicating possible tide-skew surge interactions. In those cases where dependence exists, using the skew surge does not seem to offer any advantages over the nontidal residual.