Coastal erosion of the Hawke Bay coastline from Napier to Cape Kidnappers

The southern Hawke Bay coastline from Napier to Cape Kidnappers comprises a gravel barrier beach with several major river mouths and a range of industrial, recreational and residential developments along the shoreline. There has been significant development and modification of this shoreline both due to natural causes (1931 earthquake) and human modification (groynes, gravel extraction, river diversion works). Historically, erosion of the southern portion of the shoreline has been significant, with an ongoing trend of erosion. This paper presents the findings of a coastal processes study to determine key causative factors and possible remedial solutions. This stretch of coast has extensive data sets of beach profiling extending back to the 1931 earthquake and has been the subject of numerous investigations to assess the effects of the earthquake as a predicator of possible climate change effects, with the rapid relative increase in sea level rise of up to 1.0m. It was recognised that gravel abrasion was a significant unknown cause of sediment loss and further research was carried out to improve understanding of this phenomenon with field trials. The refinement of the coastal process understanding has been carried out with the use of both a conceptual sediment budget model developed from field data and a numerical one-line model calibrated with that data to simulate shoreline evolution and to investigate causative factors and their influence.