Development of a Lagrangian sediment model to reproduce the bathymetric evolution of the Mersey Estuary |
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| Authors: | Andrew Lane |
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| Institution: | (1) Proudman Oceanographic Laboratory, Joseph Proudman Building, 6 Brownlow Street, Liverpool, L3 5DA, UK |
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| Abstract: | The development and application of a Lagrangian particle-tracking model to simulate sediment transport in the Mersey Estuary
(UK) is described. Each of the particles (up to a million in total) is advected horizontally by the 3-D tidal currents. Related
vertical movements are: (1) downwards by settlement at a prescribed velocity w
s and (2) both upwards and downwards by a distance related to the vertical eddy diffusivity. In a novel departure from traditional
practice, where initial distributions of surficial sediments are specified, all particles are introduced at the seaward boundary
of the model. Provenance studies indicate surficial sediments are overwhelmingly of marine origin. For the predominant fine
sediments, ‘cyclical convergence’ in suspended sediment concentrations is approximated after about two spring-neap tidal cycles.
Comparisons are shown between the suspended sediment concentrations and net deposition rates computed by this model against
observed values and earlier computations utilising both 1-D and 3-D Eulerian models. While all of these results are in broad
agreement, the flexibility of the Lagrangian approach for simulating flocculation, consolidation and mixed sediments illustrates
its future potential. |
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