Dejeans, Berengere S.; Mullarney, Julia C.; MacDonald, Iain T.; Reeve, Glen M.
Dejeans, B. S., Mullarney, J. C., MacDonald, I. T., & Reeve, G. M. (2017). Assessment of the performance of a turbulence closure model: along the tidally-influenced Kaipara River to the estuary, NZ. Presented at the Australasian Coasts & Ports 2017 Conference: Working with Nature, Cairns Convention Centre, Cairns, Australia.
The success of many coastal management projects hinges on the ability to predict the dispersal and settling of sediment particles. Hydrodynamic models have enabled the efficient simulation of sediment transport scenarios at large spatial scales and long time scales. However, these models have limited predictive capacity owing to an incomplete understanding of the processes involved. Turbulence has been shown to have a substantial influence on sediment transport by influencing flocculation (i.e. aggregation of particles), hence driving the behaviour of particles (e.g. deposition, erosion, mixing). Turbulence tends to promote aggregation at low shear stresses and cause floc breakups at high shear stresses. However, despite the key role of turbulence in coastal modelling, there is not a unique approach but several methods to describe turbulence, each based on a different combination of assumptions. We present modelling results exploring the performance of one closure scheme implemented in a hydrodynamic and sediment transport model, Delft3D. The assessment of the performance of the model is based on comparisons with measured data collected in the heavily sediment-laden Kaipara river, New Zealand. Data was collected in October 2013 using Lagrangian “flocdrifter” platforms released at multiple locations to capture both hydrodynamic and sediment data. In general the model was found to be able to reproduce the right order of magnitude of dissipation rates. However, turbulence characteristics in some sections of the river, usually in the vicinity of abrupt bends, are relatively poorly reproduced. Future work will aim to use the present model to improve the conceptual understanding of fundamental physical processes, in particular the effect of turbulence on flocculation, and floc formation and breakup in estuarine and riverine systems.