Lagrangian Modelling Techniques Simulating Wave and
Sediment Dynamics Determining Sand-Body Equilibria
K. Black, M. Green, T. Healy, R. Bell, J. Oldman and T. Hume
1
Introduction
Estuarine and continental shelf sand bodies develop states which, in natural unsteady conditions, equilibrate, transpose, oscillate, decay and regenerate. Dynamic adjustments may lead to long-term stability of a feature (e.g. the establishment of an estuarine flood-tidal delta) or the feature may simply metamorphose into another state (e.g. a cross-shore migrating sand bar which welds onto
the shore to become part of an open-ocean or estuarine beach). Traditionally,
the equilibrium and geomorphological features in estuaries have been mostly
explained by tidal circulation alone. However, there are estuarine features which
are governed equally by local wave processes, especially in the intertidal zones.
To be effective, numerical simulations of estuarine sedimentary systems must
therefore treat waves, currents and sometimes their interactions. For the wave
component, the models must consider wave growth in limited fetches and the
transformations in shallow water, while deformation by strong tidal streams
may also be a first-order process.
Wave resuspension of sediment inside estuaries has been mostly neglected in
favour of tidal mechanisms, particularly in comparison to the many studies of
wave-driven sediment transport on open-coast beaches and ebb-tidal deltas. In
this paper, we numerically hindcast measurements made with a self-contained
instrumented tripod in an estuary. As measurements were made on a sand bank
within a much larger physical environment, the data challenges present predictive capacity. The challenge is to predict suspended sediment concentrations at
a location which is within this much larger environment using models only. We
numerically predict all of the forcing parameters; namely height, period and
near-bed orbital motion of wind-generated waves, tidal and wind-driven currents, sediment reference concentrations and concentration profiles. Locally
measured current and wave data are employed for validation only.
Sand bank emergence/submergence, currents, wave conditions and suspended sediment concentration must all be simulated at the full estuarine spatial
scales of tens of kilometres in order to predict the sediment concentrations a few
centimetres above the sea bed at a single point. Waves have a profound influence
on sediment suspension on the sand banks and then sediment is transferred into
Sediment Dynamics Determining Sand-Body Equilibria
K. Black, M. Green, T. Healy, R. Bell, J. Oldman and T. Hume
1
Introduction
Estuarine and continental shelf sand bodies develop states which, in natural unsteady conditions, equilibrate, transpose, oscillate, decay and regenerate. Dynamic adjustments may lead to long-term stability of a feature (e.g. the establishment of an estuarine flood-tidal delta) or the feature may simply metamorphose into another state (e.g. a cross-shore migrating sand bar which welds onto
the shore to become part of an open-ocean or estuarine beach). Traditionally,
the equilibrium and geomorphological features in estuaries have been mostly
explained by tidal circulation alone. However, there are estuarine features which
are governed equally by local wave processes, especially in the intertidal zones.
To be effective, numerical simulations of estuarine sedimentary systems must
therefore treat waves, currents and sometimes their interactions. For the wave
component, the models must consider wave growth in limited fetches and the
transformations in shallow water, while deformation by strong tidal streams
may also be a first-order process.
Wave resuspension of sediment inside estuaries has been mostly neglected in
favour of tidal mechanisms, particularly in comparison to the many studies of
wave-driven sediment transport on open-coast beaches and ebb-tidal deltas. In
this paper, we numerically hindcast measurements made with a self-contained
instrumented tripod in an estuary. As measurements were made on a sand bank
within a much larger physical environment, the data challenges present predictive capacity. The challenge is to predict suspended sediment concentrations at
a location which is within this much larger environment using models only. We
numerically predict all of the forcing parameters; namely height, period and
near-bed orbital motion of wind-generated waves, tidal and wind-driven currents, sediment reference concentrations and concentration profiles. Locally
measured current and wave data are employed for validation only.
Sand bank emergence/submergence, currents, wave conditions and suspended sediment concentration must all be simulated at the full estuarine spatial
scales of tens of kilometres in order to predict the sediment concentrations a few
centimetres above the sea bed at a single point. Waves have a profound influence
on sediment suspension on the sand banks and then sediment is transferred into