Comparison of Long-Term Versus Historical Erosion Rates and Sediment Distribution Patterns for the Texas Coast

The Texas coast stretches some 590 kilometers, and includes a wide variety of shoreline types. Although there can be a dynamic range of response temporally and spatially, most of the Texas Coast has a well-documented history of shoreline and bayline erosion. But, how do current erosion rates compare to those of the past few millennia? Recently collected field data, including offshore to backbarrier core transects, are used to study facies assemblages and measure long-term erosion rates for three transgressive barrier islands: Follet's (FI), Matagorda (MI), and South Padre Island (SPI). FI and SPI are thin barriers (2m and 3m thick, respectively) experiencing rapid erosion (averaging 3 to 4 m per year), while MI (11m thick) has been a relatively stable long-term sand sink. All three barriers rest on Holocene lowstand fluvial deposits where subsidence due to compaction is negligible (ranging from .4 - 2mm/yr).

Radiometricaly-constrained sediment budgets for these barriers are used to determine the long-term shoreline retreat and to examine the contributions of different erosion mechanisms (i.e. littoral drift, fluvial sediment input, subsidence, hurricane washover, and offshore sand transport). The late Holocene backbarrier sedimentary architecture of these systems is similar: thin amalgamated washover deposits overlaying bay mud. Over longer timescales (i.e. centuries to millennia), hurricane washover has been minor. Instead, sand eroded from these barriers is mainly sequestered within the shoreface and tidal deltas. The development of numerical models to predict coastal response to accelerated sea level rise and climate controlled variations in sediment supply hinges on developing a better understanding of how and where sand is sequestered.