Modelling Extreme Events (Hurricanes) at the Seafloor in the Gulf of Mexico:

James P Syvitski1, Chris J Jenkins1, Eckart Heinz Meiburg2, Senthil Radhakrishnan2, Courtney Kay Harris3, Hernan Arango4, Tara A Kniskern3, Eric Hutton5 and Guillermo Auad6, (1)University of Colorado, INSTAAR, Boulder, CO, United States, (2)University of California Santa Barbara, Santa Barbara, CA, United States, (3)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (4)Rutgers University, New Brunswick, NJ, United States, (5)Community Surface Dynamics Modeling System, Boulder, CO, United States, (6)U.S. Bureau of Ocean Energy Management, Sterling, VA, United States
Abstract:
The subsea infrastructure of the N Gulf of Mexico is exposed to risks of seabed failure and flowage under extreme storm events. Numerical assessments of the likelihood, location and severity of those phenomena would help in planning. A project under BOEM, couples advanced modelling modules in order to begin such a system. The period 2008-10 was used for test data, covering hurricanes Gustav and Ike in the Mississippi to De Soto Canyons region.

Currents, tides and surface waves were computed using the Regional Ocean Modeling System (ROMS) and river discharges from WBMsed. The Community Sediment Transport Model (CSTMS) calculated the concurrent sediment erosion-transport-deposition. Local sediment properties were from the dbSEABED database. The preferred paths of near-bottom sediment flows were based on a stream analysis of the bathymetry. Locations and timings of suspended sediment gravity flow were identified by applying energy flow ignition criterea. Wave-induced mass failure and subbottom liquefaction were assessed using a bevy of marine geotechnical models. The persistence, densities and velocities of turbidity flows yielded by the disruption of the sediment masses were calculated using high-Reynolds Number adaptations of LES/RANS-TURBINS models (Large-Eddy Simulation / Reynolds Averaged Navier-Stokes).

A valuable experience in the project was devising workflows and linkages between these advanced, but independent models. We thank H Arango, T Kniskern, J Birchler and S Radhakrishnan for their help in this.

Results: as known, much of the shelf sediment mantle is suspended and/or moved during hurricanes. Many short-lived gravity-flow ignitions happen on the shelf; only those at the shelf edge will ignite into fast, erosive currents. Sediment patchiness and vagaries of hurricane path mean that the pattern alters from event to event. To understand the impacts on infrastructure, a numerical process-based modelling approach will be essential – along the lines we explored.

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