Measuring Historical Shoreline Change, Applying New Polynomial Change Models: Southeast Oahu, Hawaii

Digital aerial photo mosaics and NOAA topographic survey charts (t-sheets) are used to map historical shoreline positions on southeast Oahu, Hawaii. The new PX (Polynomial in alongshore X) and PXT (Polynomial in X and Time) shoreline change rate methods are applied to calculate shoreline change rates from the time series of historical shoreline positions. These new methods utilize all historical shoreline data from a beach to calculate shoreline change rates and can find acceleration in the shoreline change rate with time. The methods are shown here and in previous works to produce more parsimonious models and more statistically significant and defensible rates than the previously used ST (Single-Transect) shoreline change rate calculation method. The ability to model acceleration in shoreline change rates with time provides insight into shoreline change processes, which was previously theoretical or observed in only small-scale studies. An overview of the methods is presented along with results from shoreline change analysis of four beach study sites on the southeast Oahu, Hawaii, shoreline.