QUANTIFYING SPATIO-TEMPORAL BEACH MORPHODYNAMICS USING THE SEDIMENT VOLUME CENTER OF MASS

For more than a half-century investigators have relied on shoreline position, and more recently volumetric approaches, as proxies for assessing temporal beach change. The shoreline's commonplace accessibility on historic maps and photographs, and the later advent of GPS and laser altimetry (LiDAR) technologies are principal reasons behind these trends. Studies, however, have expressed mixed results in evaluating the shoreline as a suitable proxy for overall beach change. Moreover, while bulk volume does better reflect overall change versus using shoreline position alone, it is neither sufficient to completely describe temporal beach evolution.

In this presentation I introduce a new proxy metric that attempts to further refine beach change analysis beyond that provided by commonly employed shoreline position and bulk volume approaches. This new proxy is called the volumetric center of mass. The volumetric center of mass (CM) maps beach sediment volume into a single point in space--its physical center of mass--whose position is then tracked through time. It is surmised that the CM might provide a more detailed and precise accounting for the temporal sediment redistributions, gains, and losses that can occur within a beach's active transport zone. Here, I undertake to demonstrate its usefulness as an alternative, and/or a complement, to traditional shoreline position, and more recent bulk volume, measures.