Award: OCE-1828920

The rains of Hurricane Harvey in September 2017 produced record flooding of the Brazos River, which ranks second to the Mississippi River in the volume of freshwater and river-borne sediments carried to the Gulf of Mexico. The movement and ultimate fate of sediments delivered by the Brazos to the Gulf have long been of interest as these sediments carry chemicals as well as pollutants to the nearshore area of the Gulf. It has been theorized that these sediments are initially deposited in the shallow waters off the river mouth, and are subsequently carried offshore by Gulf currents. Exactly where Brazos-borne sediments may eventually settle on a long-term basis is a matter of speculation. One candidate put forth as an ultimate depocenter of sediments carried into the Gulf by the Brazos, and other rivers emptying into the western Gulf, is an offshore band of fine sediments that stretches from 70 to 270 km west of the Brazos River mouth and is often referred to as the Texas Mud Blanket. While taking part in a September 2017 scientific cruise studying how river-borne particles affect the carbonate chemistry of coastal waters, our team was afforded the remarkable opportunity of acquiring sediment cores in the coastal area offshore of the Brazos River while the flooding produced by Hurricane Harvey was subsiding. This RAPID project was initiated to take this rare flooding opportunity to study the fate of the Brazos’s sediments in relation to the Texas Mud Blanket. The study allowed analysis of the cores collected during the September 2017 cruise, and revealed that a historically large volume of sediments had been deposited in the nearshore area off the Brazos River mouth during the passage of Hurricane Harvey and the continued flooding that followed. With an average depth of roughly 25 cm, this band of recently deposited sediment dwarfed sediment bands deposited off the Brazos during previous flooding events. Analysis of sediment cores acquired in subsequent cruises (in October 2017 and July 2018) revealed that this near-shore sediment band, laid down in the wake of Hurricane Harvey, was subject to erosion and tended to migrate to the southwest, in general direction of the Texas Mud Blanket. We estimate that the migration proceeded at a rate of 1-2 km per year, which is the first estimate of the rate at which the sediment deposited off the Brazos migrates away from its initial zone of deposition. As a follow-on to this finding, we plan to examine how the coastal currents and wave action in the Gulf act to erode and move this sediment. This will form a better understanding of where this sediment is eventually deposited. Last Modified: 10/19/2020 Submitted by: Zhaohui 'aleck' Wang