| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | February 28, 2018 |
| Latest Amendment Date: | February 28, 2018 |
| Award Number: | 1829221 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Deborah K. Smith
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | March 1, 2018 |
| End Date: | February 28, 2019 (Estimated) |
| Total Intended Award Amount: | $44,996.00 |
| Total Awarded Amount to Date: | $44,996.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
400 HARVEY MITCHELL PKY S STE 300 COLLEGE STATION TX US 77845-4375 (979)862-6777 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1001 Texas Clipper Rd Galveston TX US 77553-1675 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Hurricane Harvey 2017 |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The transport and fate of sediment carried by rivers to the coastal ocean is of great ecological and societal importance. River input is the primary source of land-derived sediment to the marine environment. These particles have significant impacts on the health of coastal ecosystems and the geology and bathymetry of coastal oceans and shipping channels. They directly and indirectly affect fisheries and navigation. This research focuses on the movement of sediments carried into the Gulf of Mexico, via the Brazos River, during the unprecedented rainfall and flooding event that occurred during Hurricane Harvey. The Brazos River ranks as the second largest contributor of nutrients and organic matter to the Gulf of Mexico, after the Mississippi River. Unlike the Mississippi, however, most sediment delivered to the Gulf of Mexico from the Brazos is carried during flooding events like that which accompanied Hurricane Harvey. Little is known about the fate of this sediment. It is not clear if it is retained in the coastal zone, where the nutrients and chemicals it carries affect the coastal environment, or is carried offshore and deposited in the deep waters of the Gulf of Mexico. Through intensive sampling of sediments just offshore the mouth of the Brazos River and further offshore in the Gulf of Mexico in what is known as the Texas Mud Blanket, this project will determine the principal repository of sediments delivered to the western Gulf of Mexico by a major Texas river.
The overall goal of this research is to investigate the hypothesis that flood-borne sediment from the Brazos River is initially deposited in the coastal zone and subsequently mobilized and carried offshore with a large fraction of it being deposited in the Texas Mud Blanket. The work builds on the analysis of sea-bottom sediment samples collected in 2017 during flooding associated with Hurricane Harvey. This new program will include two sampling cruises to augment already collected data. The first cruise will entail acquisition of ~25 cores that will indicate sediment deposition and transport in the near-shore region near the Brazos River mouth. Preliminary work indicates that much of the initial deposition of Brazos River sediment occurred east of the original sampling region. The second cruise in will collect additional Brazos region cores and expand sampling into the Texas Mud Blanket, with the goal of documenting changes in Brazos sediment deposition from the Hurricane Harvey flooding. During both cruises, complementary hydrography data will be collected. This includes water column velocities and suspended sediment loads. Provenance of individual layers, within the sediment samples and box cores, will be determined by digital photos and x-radiographs of intact core slabs that show sediment fabric and structures. To differentiate Gulf of Mexico from Brazos River sediments, sub-samples of collected cores will be geochemically analyzed and profiled for short-lived-radioisotope geochronology, water content, grainsize distribution, and mercury and carbonate content. These indicators will help identify the origin of the sediments deposited in the system.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
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
Modified by: Timothy Dellapenna
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