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J. Mar. Sci. Eng. 2014, 2(2), 336-369; doi:10.3390/jmse2020336
Article

A Hydrodynamic and Sediment Transport Model for the Waipaoa Shelf, New Zealand: Sensitivity of Fluxes to Spatially-Varying Erodibility and Model Nesting

1,* , 1
 and 2
1 Virginia Institute of Marine Science, The College of William & Mary, P.O. Box 1346, 1375 Greate Road, Gloucester Point, VA 23062, USA 2 National Institute of Water and Atmospheric Research, 301 Evans Bay Parade, Hataitai, Wellington 6021, Private Bag 14901, Wellington, New Zealand
* Author to whom correspondence should be addressed.
Received: 4 December 2013 / Revised: 7 February 2014 / Accepted: 14 February 2014 / Published: 3 April 2014
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Abstract

Numerical models can complement observations in investigations of marine sediment transport and depositional processes. A coupled hydrodynamic and sediment transport model was implemented for the Waipaoa River continental shelf offshore of the North Island of New Zealand, to complement a 13-month field campaign that collected seabed and hydrodynamic measurements. This paper described the formulations used within the model, and analyzed the sensitivity of sediment flux estimates to model nesting and seabed erodibility. Calculations were based on the Regional Ocean Modeling System—Community Sediment Transport Modeling System (ROMS-CSTMS), a primitive equation model using a finite difference solution to the equations for momentum and water mass conservation, and transport of salinity, temperature, and multiple classes of suspended sediment. The three-dimensional model resolved the complex bathymetry, bottom boundary layer, and river plume that impact sediment dispersal on this shelf, and accounted for processes including fluvial input, winds, waves, tides, and sediment resuspension. Nesting within a larger-scale, lower resolution hydrodynamic model stabilized model behavior during river floods and allowed large-scale shelf currents to impact sediment dispersal. To better represent observations showing that sediment erodibility decreased away from the river mouth, the seabed erosion rate parameter was reduced with water depth. This allowed the model to account for the observed spatial pattern of erodibility, though the model held the critical shear stress for erosion constant. Although the model neglected consolidation and swelling processes, use of a spatially-varying erodibility parameter significantly increased export of fluvial sediment from Poverty Bay to deeper areas of the shelf.
Keywords: numerical modeling; sediment transport; erodibility; model nesting; Waipaoa shelf; New Zealand numerical modeling; sediment transport; erodibility; model nesting; Waipaoa shelf; New Zealand
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Moriarty, J.M.; Harris, C.K.; Hadfield, M.G. A Hydrodynamic and Sediment Transport Model for the Waipaoa Shelf, New Zealand: Sensitivity of Fluxes to Spatially-Varying Erodibility and Model Nesting. J. Mar. Sci. Eng. 2014, 2, 336-369.

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