Transgressive Ravinement versus Depth of Closure: A Geological Perspective from the Upper Texas Coast

Abstract The upper Texas coast is one of the most populated areas along the Gulf of Mexico. Three dynamic barriers along this section of coastline (Bolivar Peninsula, Galveston Island, and Follets Island) have a well-documented history of shoreline change. Numerous engineering studies incorporating both sedimentological data and numerical models have been established for this system to understand sediment fluxes. However, rarely have previous studies examined sediment fluxes for the upper Texas coast in light of certain fundamental concepts of coastal geology. Here, we discuss the current theory and understanding of barrier island dynamics from a geologic standpoint as they relate to sediment budgets for the upper Texas coast. From sediment cores, we quantify both shoreface and washover sand fluxes, which previously were not incorporated as sand sinks into sediment budgets for this system. Shoreface sand fluxes represent a sizable portion of the total budget, whereas modern washover sand fluxes are minimal. Until now, a depth of closure (beyond which sediment transport is negligible) of 4 m has typically been used; however, our data suggest a depth of at least 8 m would be more appropriate. We show that the combined upper and lower shoreface has the potential to sequester ~160,000 ± 39,000 m3/y of sand, equaling ~17% of the entire calculated sediment flux and ~37% of the total longshore transport flux for the upper Texas coast, based on previous studies. Therefore, we recommend revised approaches to future sediment budget studies in order to establish more robust analyses. Ultimately, it will be crucial to use both engineering principles and geologic concepts to construct an accurate and realistic scenario for coastal restoration projects.

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