Tectonic and Climate-Controlled Hazards on the Shores of Hawke's Bay, New Zealand

Abstract

Komar, P.D. and Harris, E., 2022. Tectonic and climate-controlled hazards on the shores of Hawke's Bay, New Zealand. Journal of Coastal Research, 38(6), 1075–1095. Coconut Creek (Florida), ISSN 0749-0208. Elevations of the Hawke's Bay shore on the Pacific coast of New Zealand were altered by an earthquake in 1931, such that at its north end the gravel beach and shore-front properties were raised by 2 m, while elevations dropped by 1 m at its south end. Along the elevated shore, the morphology was altered from a low-lying gravel spit that had experienced frequent overwash events, changed to a gravel barrier ridge where its increased stability permitted construction of expensive homes. The central stretch of shore, where there was minimal change in elevations, continues to experience wave overtopping during storms and high tides, just as had occurred prior to the earthquake. The southern-most shore, where subsidence took place, experiences substantial property damage during winter storms. With projections of accelerated rates of rising sea levels and increased storm intensities produced by global warming, concerns are that the developed shore of the elevated gravel ridge will again suffer from erosion and overwash flooding. Analyses have been undertaken of the hourly measured tides, waves, and calculated swash run-up levels on the beaches, combined to yield a record of hourly total water levels at the shore. Its extremes have been compared with the elevations of the surveyed gravel ridges to yield assessments of the potential erosion and flooding hazards. Still greater hazard assessments have been based on a recognition that the morphologies of the surveyed ridges provide direct evidence for the most extreme water levels that occurred at times of major storms in the distant past, prior to the availability of the process data. Assessments of hazards expected 100 years into the future have included projections of both rising sea levels and evidence for increasing storm-wave heights.