SEA LEVEL RISE TRIGGER TO WIDESPREAD COASTAL ARMORING ON HAWAIʻI’S SHORES

In Hawaiʻi, private property owners may be given special consideration to armor their beachfront property if their home or other structure is in danger of immediate damage (within 20 feet of an eroding shoreline). However, studies have shown that over time armored shorelines result in beach narrowing and loss. When considering sea level rise (SLR), the number of properties that could harden the shoreline increases with these policies, placing the future of the beach in the hands of property owners and their growing need to protect their investments and a willing management regime. To identify when and which communities are most vulnerable to the risks involved with future erosion due to SLR, we conducted a spatial analysis on the north and eastern shores of Oʻahu. In ArcGIS, we projected future erosion hazard zones using the model of Anderson et al. (2015), for 0.15, 0.3, 0.6, and 0.92 meters increase in sea level. These projections were buffered to 20 feet and intersected with digitized development layers that overlay orthorectified mosaics. The results show that as little as 0.15 m of SLR will trigger a cascade of seawall applications, potentially increasing shoreline armoring by an order of magnitude and placing at risk valuable and sensitive beach resources. This implies that the most critical scenario for which communities must prepare is the soonest SLR scenario with priority given to the areas with the greatest potential impact.