Abstract

Chronic erosion leads to loss of property and critical habitats, and it restricts public access along developed coasts. There are, currently, no practical methods for estimating the spatial extent of erosion hazard, despite the fact that increased sea level rise (SLR) over the current century is likely to contribute toward more land being exposed to future erosion. This study creates a new model which provides estimates of exposure to erosion on a local geographic scale. This new method is a valuable tool for the coastal community because of its ease of implementation and because it uses historical shoreline trends, information that is widely available.

This study applies the new model to all sandy shorelines of the Hawaiian Island of Kauai. Application to an entire island serves to: 1) ensure that the model can be successfully applied to diverse geologic and wave settings; and 2) provide erosion hazard projections for improved coastal management both for Kauai County and as part of the Hawaii legislatively-mandated Act 83, which requires the creation of the Interagency Climate Adaptation Committee (ICAC) tasked with creating a climate adaptation report on the impacts of SLR.
Modeled erosion hazard areas are graphically presented in map form to identify areas that are vulnerable to erosion and which can be used to improve the decision-making process in coastal management. The probability of future exposure to erosion is shown as geographic information system (GIS) layers. These layers are incorporated into an online tool that displays erosion hazard layers, along with other SLR-related hazards. The website (http://www.pacioos.hawaii.edu/shoreline/slr-icac/) is currently password protected while this tool is in draft form; public release is expected at the end of year 2017.

Erosion hazard layers for the years 2030, 2050, 2075, and 2100 were created for all sandy shorelines of Kauai Island, Hawaii under the IPCC “business-as-usual” SLR scenario. Results for Kauai indicate that all four regions of the island (North, East, South, West) will have more areas experiencing coastal retreat, and the rates of retreat will become more intense over the current century. The percent of Kauai shorelines included in the study that show retreat (those with a negative long-term shoreline change trend) increased from 73% historically, to 86% by the year 2050, to 91% by the year 2100. Erosion hazard layers produced by this study will be widely available to government agencies and the general public, and will be essential in assessing vulnerability to erosion with increased SLR.