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Michael Slattery, Texas Christian University (United States)
Lee Todd, Texas Christian University (United States)
Jonathan Phillips, University of Kentucky (United States)
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Our focus in this paper is on the lower reaches of the 46,000 km2 Trinity River basin, Texas. Previous work has shown that the upper and lower basins of this system are decoupled in the sense that relatively little upper-basin sediment is being transported to the river mouth. The implications of such alluvial buffering are profound. Because sediment and freshwater fluxes to the coastal zone are typically measured or estimated based on gaging stations well upstream of the coast, and upriver from sediment bottlenecks, fluvial sediment delivery to the coast can in many cases be substantially overestimated. In this paper we use ground penetrating radar (GPR) along with traditional coring methods to quantify sedimentation and accretion rates in the delta. Data show accretion rates of between 1.1 to 1.8 mm yr-1. Such sedimentation rates are inadequate to keep pace with coastal submergence, accounting for the wetland loss and marsh shoreline erosion occurring in the lower delta. Furthermore, contemporary sediment delivery by the Trinity River is not adequate to account for the Holocene growth of the delta. Trinity River inputs appear to be supplemented by reworking and resuspension of local Trinity Bay and delta sediments, autochthonous organic matter, sediment delivery from tributaries in the delta area, and (locally) slopewash from adjacent terraces.
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