USING SPATIAL STATISTICS TO EXAMINE MORPHODYNAMIC AND SEDIMENT BUDGET RESPONSES IN A DYNAMICALLY RESTORED BEACH-FOREDUNE SYSTEM (Invited Presentation)

Spatial statistics are generally underutilized in coastal geomorphology, despite offering great potential for identifying and quantifying spatial-temporal trends in landscape morphodynamics and process-response regimes. In particular, local Moran’s I_i provides a statistical framework for detecting clusters of significant change in an attribute (e.g., surface erosion or deposition) and quantifying how this changes over space and time. This study presents an analysis of spatial-temporal patterns in sediment volume changes in a beach-foredune-transgressive dune complex following removal of invasive marram grass (Ammophila spp.). Results are derived by detecting significant changes in post-removal repeat DEMs derived from laser total station surveys and airborne LiDAR. The 10,320 m² study site was separated into discrete, linked geomorphic units (beach, foredune, transgressive dune complex) to facilitate sub-landscape scale analysis of volumetric change and sediment budget responses. Difference surfaces derived from a pixel-subtraction algorithm between interval DEMs and the baseline DEM were filtered using the local Moran’s I_i method and two different spatial weights, or threshold distances, (TD, 1.5 and 5m) to detect statistically significant change. The Moran’s I_i results were compared with those derived from a more spatially uniform geostatistical method based on a simpler student’s t distribution threshold for change detection. Morphodynamic patterns and volumetric estimates were similar between the strictly geostatistical method and Moran's I_i at TD (5 m) while the smaller TD (1.5 m) consistently indicated volumetric changes of less magnitude. The larger TD is suggested to best reflect site dynamics spatially while the smaller TD provided volumetric changes consistent to field observations. All methods showed foredune accretion following removal and increasing sediment volumes into the spring via deposition at the crest and on lobes in the lee, despite erosion on the stoss slope and dune toe. Generally, the foredune became wider by landward extension and the seaward slope recovered from erosion to a similar height and form to that of pre-restoration despite remaining free of vegetation.