A regional analysis of tide-surge interactions during extreme water levels in complex coastal systems of Aotearoa New Zealand

Tide-surge interaction (TSI) is a critical factor in assessing flooding shallow coastal systems, particularly estuaries and harbours. Non-linear interactions between tides surges can occur due to the water depth bed friction. Global investigations have been conducted examine TSI, but its occurrence impact on levels Aotearoa New Zealand (NZ) not extensively studied. Water level observations from 36 tide gauges across diverse coast of NZ were analysed determine location TSI. Statistical analysis numerical modelling data both inside outside estuaries, focusing one estuary (Manukau Harbour) TSI estuarine morphology co-occurrence rate extreme events. was found at most sites primarily affects timing largest relative high tide. There no regional patterns associated with tide, non-tidal residual, or skew-surge regimes. The strongest occurred inner locations correlated intertidal area. magnitude varied depending method used, ranging -16 cm +27 cm. Co-occurrence rates same 20% 84%, modulating by affecting tidal amplification. results highlight importance investing more extensive gauge network provide longer highly populated coastlines. incorporation hazard projections would benefit accurate detailed observations, morphological complexity. occurs along has significant locations. modulates Therefore, further investment needed incorporate projections.