Small-scale morphodynamics of maintained and unmaintained beaches on Mustang Island, Texas

In the State of Texas, the public is guaranteed free and unrestricted access to Gulf of Mexico beaches from the mean low tide line to the vegetation line. This access includes vehicular traffic and provides for grooming to create a driving lane which is both costly and unnatural so the study of its effects on beach morphology are important to city planners, local taxpayers, and beachgoers alike. Therefore, the purpose of this study is to assess the impacts of beach maintenance practices on the backbeach with the intent of determining maintenance practices that foster the healthiest morphology while providing unrestricted access.

Two Mustang Island beach sites were chosen for their environmental similarities, but maintenance differences; one site was frequently maintained and the other site was completely unmaintained. The sites were scanned during peak maintenance activity using a terrestrial laser scanner (TLS), were ground-truthed, registered, and georeferenced using a Real-Time Kinematic (RTK) GPS, and were analyzed in ArcGIS to determine how surface elevations and vegetation were affected by maintenance.

The Digital Surface Model (DSM) for the maintained site showed a distinctly scarped profile, sparse vegetation, a vast backbeach driving lane, and little-to-no coppice mounds while the DSM for the unmaintained site showed a well-developed and gently sloping coppice area with dense vegetation and a narrow backbeach driving lane. From July to October, the entire unmaintained site remained stable with small gains in sediment consistent with expected summer onshore sediment transport while the maintained site experienced losses in the driving lane area from scraping and large gains in the coppice area from driving lane sand pushed against the dune toe during maintenance.

Although short in duration, this study implied that maintenance practices could be improved by maintaining a narrower driving lane. This would promote embryo dune advancement and vegetation growth for a more dissipative backbeach profile and a more stable foredune which would better insulate landward developed areas from storm-generated washover flooding. Finally, the residual comparative analysis between Real-Time Kinematic (RTK) GPS measurements and the raster products showed high levels of accuracy suggesting promise for similar future studies using this methodology.