Quantifying shoreline change on Hawai‘i using 3D aerial imagery

Rose Hart and Ryan Perroy, University of Hawai‘i at Hilo

Student controlling drone rising above a field.Rose Hart controls an unmanned aerial vehicle, or drone, to collect new coastal imagery on Hawai‘i Island.

As the largest island in the Hawaiian archipelago, Hawai‘i Island has over 265 miles of coastline (and growing), ranging from sandy beaches to tidepools within lava fields to steep cliffs. There is often strong pressure to place homes and other developments very close to these shorelines. Hawai‘i County does have coastal zone setbacks, but these are currently relatively short at 20 to 40 feet from the 'certified shoreline.' There is no research that shows this distance to be sufficient, especially given that climate change and sea level rise are expected to increase rates of shoreline movement due to increased coastal erosion. Hawai‘i Island has never had a comprehensive shoreline assessment of coastal vulnerabilities or any systematic monitoring of long-term shoreline change rates, which puts it in a weak position for adapting to the potential impacts of sea-level rise (SLR), building community resilience, and conserving key coastal resources and environments.

Surveying equipment set out on rocky beach edgeGround-based surveys combined with UAV images provide an accurate shoreline map.

This project will quantify historic and current coastal erosion rates for selected priority areas representing a variety of Hawaiian coastal environments at different stages of development, including sea cliffs, low-ying and subsiding coastal lava fields, and coral-sand beaches. Existing shoreline records, including historic aerial photographs and coastal surveys, are being combined with new coastal imagery and three-dimensional data sets collected from unmanned aerial vehicles (UAV) and other survey platforms to determine past and current shoreline change rates. These data will then be merged with SLR projections and other geospatial layers to estimate future impacts.

Erosion rates and SLR projections will be incorporated into the county's GIS database and made available to the public through the statewide GIS system. These data will provide a visualization tool for communities and county workers to understand local impacts of SLR and consider necessary adaptations. There has already been significant interest in this project, and we hope that it can provide a model of how to use data from UAV flights to provide timely and high-quality shoreline change information. This project is part of the PI-CASC Manager Climate Corps program.

Quick Summary

      Hawai‘i Island has over 400 km of geologically diverse shoreline, most of which has never had a thorough assessment of coastal vulnerabilities or shoreline movement. This makes it more difficult for the county to develop adaptation and conservation plans, including standards for prudent shoreline development.
      Our work quantifies historical and current coastal erosion rates by combining historical aerial photos and coastal records with current imagery and three­dimensional data collected from ground surveys and unmanned aerial vehicle flights.
      Our results will allow us to estimate future change over a wide variety of shoreline types, and projections will be publicly available through state and county GIS systems. By using these visualizations management agencies and local residents will better be able to understand the local impacts of sea level rise, and how best to adapt.

PI-CASC logo UH Hilo logo Dept of Interior logo

This project was supported by the Pacific Islands Climate Adaptation Science Center (Cooperative Agreement #G15AP00059 from the US Geological Survey). For more information, please contact Rose Hart (rosehart@hawaii.edu) or Ryan Perroy (rperroy@hawaii.edu). To learn more about climate science at PI-CASC, contact David Helweg at dhelweg@usgs.gov or visit: https://nccwsc.usgs.gov/pacificislandscsc.