Award: OCE-1829221

What are the major goals of the project? This project focuses on the secondary migration of sediments carried into the Gulf of Mexico from the Brazos River during the extreme flooding that occurred during Hurricane Harvey from its initial proximal depositional site towards, potentially towards a distal depo-center . The Brazos ranks as the second largest contributor of nutrients and organic matter (after the Mississippi) to the Gulf of Mexico. Most of the sediments delivered to the Gulf of Mexico from the Brazos are carried during extreme flooding events, such as Hurricane Harvey, and initially deposited on the shelf, proximal to the river mouth. However, little is known about the ultimate fate of this sediment. Is it retained in the coastal zone, where its stored carbon and other chemicals, including pollutants, will affect the coastal environment, or is it carried offshore and ultimately deposited in the deep waters of the Gulf of Mexico? A hypothesized repository of riverine sediments entering the western Gulf of Mexico is an offshore areas known as the Texas Mud Blanket, an early Holocene depo-center of the combined Brazos and Colorado Rivers. Previous work has suggested that flood-borne sediments from the Brazos River are initially deposited in the near-shore region and eventually migrate to the Mud Blanket. To better understand the migration of flood-borne sediments entering the western Gulf of Mexico, the project work is directed at the following objectives: Document the initial deposition and any subsequent migration of the sediments carried into the western Gulf of Mexico by the floodwaters of the Brazos River during Hurricane Harvey, and Determine the fate (after a period of two years) of Brazos River sediment carried into the Gulf of Mexico and the approximate rate at which this sediment is moved offshore. Major Activities: The project was motivated by visual inspection of box cores taken from the R/V Pelican on September 10, 2017, during the waning days of the flooding from Hurricane Harvey. Collected from 15 different sites across and along the Brazos River subaqueous delta, the cores showed a surface layer of deep red sediment, characteristic of material in the Brazos drainage basin. To trace the movement and dispersion of this near-shore ?flood layer? of material deposited during the Brazos flooding, follow-up coring cruises were conducted on October 29, 2017 and July 10, 2018. A third cruise is slated for the summer of 2019. The cores acquired thus far have been subject to a suite of analyses, including: x-radiography, grain size analyses, water content, Hg content. Short-lived radio-isotope analyses (e.g. 210Pb) has yet to be conducted. Significant results: The analysis carried out thus far indicate that the near-shore flood layer deposited during Hurricane Harvey extended to an average depth of roughly 25 cm, which exceeds the yearly average depth of sediment deposited in the nearshore zone off the Brazos River mouth by about a factor of four. Data from the collection of cores reveal that, after initial deposition, the flood layer has migrated at least 1 km offshore as well as at least 1 km in the along-shore direction to the southwest. With another season of cold fronts, we anticipate that the deposit will continue to migrate offshore and towards the west. A summary of the findings was presented as a poster (attached as a supporting file) at the Fall 2018 AGU Meeting in Washington DC by Christena Hoelscher. What opportunities for training and professional development has the project provided? This project has was both Christena Hoelscher?s undergraduate Senior Aggie Scholars Thesis. This project als also become part of Christena?s Ph.D. dissertation. The RAPID Cruises 1 have been conducted by a combination of TAMUG Undergraduate Marine Science undergraduates, graduate students and in July 2018 included 16 Korean undergraduates from Inha University. The TAMUG Coastal Geology graduate students mentored the Inha students on cruise associated research projects. During this academic year, Oscar Cavazos, a Hispanic student, has been working as student research assistant with Christena on the analyses of her cores and will be participating on the final follow up cruise in 2020. How have the results been disseminated to communities of interest? The findings were presented as a poster (attached as a supporting file) at the Fall 2018 AGU Meeting in Washington DC by Christena Hoelscher. What do you plan to do during the next reporting period to accomplish the goals? To further quantify the movement of the sediment deposited off the Brazos River mouth in the wake of Hurricane Harvey, we will conduct a fourth coring cruise in summer 2019. We will also finalize the analysis of the core acquired, including conducting 210Pb, Loss on Ignition TOC, and Hg analyses . The findings will be summarized as part of Christena Hoelscher?s thesis as well as in a subsequent paper to be submitted for publication. Last Modified: 06/05/2019 Submitted by: Timothy Dellapenna