A Deeper Look into How eCoast Conducts Coastal Hazard Assessments

Along the coastlines of New Zealand, different regional councils have varying coastal hazard policies pertaining to setbacks, coastal inundation, coastal erosion, as well as tsunami and flooding hazards. Here at eCoast, we work with Council Planners to understand the exact requirements stated in the policies for the purpose of collating site-specific information relevant to gaining building consents for our clients.

Site specific Coastal Hazard Assessments (CHAs) outline a consistent list of key information, recommended methodologies, and key parameters that councils require to make informed decisions in a consistent manner.

Some councils have conducted their own shoreline retreat and inundation investigations for shorelines within their regions and have provided setbacks, inundation, erosion, and flooding data, which streamlines the CHA process. Yet, coastal engineers are still required to provide site specific CHAs to confirm and/or refute the best available knowledge.

Using Coastal Hazard and Climate Change guidance provided by the Ministry for the Environment, information from the Intergovernmental Panel on Climate Change (IPCC), data from the council geomaps, documentation from NIWA and many others, as well as by downloading wind and wave data from NOAA and ECMWF, which all provides tidal information, storm tide data, Sea Level Rise scenarios, and wave run-up and overtopping data, we are able to use our in-house coastal hazard calculators to generate extreme water level heights along open coastlines as well as within harbours and estuaries. These calculations provide site specific inundation heights, which when combined with SLR scenarios to a 100-year planning horizon, as well as freeboard heights, provides site specific minimum finished floor levels.

Further, historic shorelines are analysed from aerial imagery sourced from Retrolenz, LINZ, and Google Earth. These images are georectifed and shorelines digitised to provide historic shoreline retreat rates and information pertaining to the energetic nature of the environment. These rates are plugged into cliff retreat calculators, which provides, as the name suggests, a shoreline retreat rate into to the future utilising the latest IPCC Sea Level Rise rates to a 100- year planning horizon.

The collated information on Coastal Erosion, Inundation, Flooding, and Tsunami are critically discussed in a concise report format and presented in a manner suited for individual councils.