CSDMS 2014 annual meeting poster Julia Moriarty
Buoyant and Gravity-Driven Transport on the Waipaoa Shelf: Model Evaluation and Sensitivity Analyses
Courtney Harris, Virginia Institute of Marine Science Gloucester Point Virginia, United States. ckharris@vims.edu
Carl Friedrichs, Virginia Institute of Marine Science Gloucester Point Virginia, United States. cfried@vims.edu
Mark Hadfield, National Institute for Water and Atmosphere Wellington , New Zealand. m.hadfield@niwa.co.nz
Abstract:
Riverine deposits on continental shelves display terrestrial signatures, although the marine environment may overprint them. Partitioning between various transport mechanisms (dilute suspension vs. gravity-driven) may influence the location and characteristics of these deposits. The MARGINS Waipaoa River shelf initiative investigated these issues by conducting a thirteen month field campaign, and an ongoing numerical modeling study of the Waipaoa River shelf, New Zealand. We used two numerical models to analyze sediment fluxes and fate on the continental shelf during a time when three large floods and multiple high wave events occurred, from January 15, 2010 – February 15, 2011.
Water-column fluxes were estimated using the Regional Ocean Modeling System- Community Sediment Transport Modeling System (ROMS - CSTMS). This three-dimensional hydrodynamic-sediment transport numerical model accounted for gravity-driven transport by incorporating sediment concentrations into the model’s equation of state. Because ROMS did not resolve fluxes within the thin wave-current boundary layer, however, we also used a linear-bed turbid layer model based on the Chezy equation, which balances friction and gravity.
Buoyant fluxes within the water column model distributed sediment along-shore to the inner and mid-shelf, depositing material up to about 50 m water depth. Wave- and current- supported gravity flows, in contrast, could export sediment to long-term shelf depocenters (50 – 70 m water depth) and the continental slope. Hydrodynamic and seabed observations of sediment fluxes and gravity flows will be compared to sensitivity tests. Preliminary results indicated that erodibility parameterization and sediment settling velocity significantly affected buoyant sediment fluxes. In contrast, estimates from the near-bed turbid layer model were sensitive to assumptions about the distribution of sediment delivery from the river in terms of the initial deposit and percentage of the riverine load available for gravity driven transport.
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