Climate Change and Gravel Beach Responses: Hawke’s Bay, New Zealand

In 1931 a major earthquake altered elevations along the shores of Hawke’s Bay, raised by 2 m at the north end of the study area, decreasing alongshore with 1-m subsidence at the south end. While the uplifted gravel beaches created stable barrier ridges, now developed with homes, concerns are that with projected accelerated rates of rising sea levels and increasing storm wave heights, erosion and overwash impacts will return. Analyses have been undertaken of the measured tides, waves, and calculated swash runup levels on the beaches, combined to yield a record of hourly total water levels at the shore. Its extremes are compared with the elevations of surveyed beaches and gravel ridges, to project future property hazards. In that little more than a decade of measured waves were available for our analyses, the morphologies of the ridges provided evidence for past more extreme storm events and water levels, which had occurred in the 8 decades since the earthquake, and land-elevation changes.