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into form and shear components for predicting erosion. Multiple grain sizes are
represented, including both cohesive and non-cohesive particles.
The morphodynamic change model is based on a variation of Exner's
equation and is coupled to a bed-armoring algorithm (Reed et al. 1996).
Together, they track changes in bed elevation and grain size composition. For
long-time simulations, the morphodynamic changes are reflected in the
hydrodynamic model by changing the bottom profile. In addition to the three
basic model components (hydrodynamics, transport, and morphology), the
model also includes representation of the time evolution of the bed. This allows
the sediment grain-size distribution at the bed to be known over the whole
domain for each time-step. Resolution of the grain size distribution in the bed
allows bed armoring to be tracked, which greatly improves the validity of the
computed erosion, transport, and deposition of all sediment size classes.
M3D is designed to be a general-purpose, process-based local coastal
hydrodynamic, sediment transport and morphodynamic model. It can be applied
in a variety of coastal settings including channels approaching inlets from both
the seaward and landward sides, providing time-dependent channel response
both o event-scale and long-term waves and to wind and current forcing.
3.
Sediment Transport Validation
The M3D model hydrodynamic and sediment transport components were tested
against numerous data sets. The laboratory data sets of Ribberink et al. (1994)
and field measurements of Wright (1999) were used for the validation.
The model successfully reproduced the time-averaged suspended sediment
profile measurements in flow tunnel experiments of Ribberink, et al. (1994).
The experimental results represent a 1-m wave with 5-s period over a bed of
0.2 mm quartz sand. Figure 1 compares model predictions for a simulation of
these conditions with the measurements, showing excellent agreement.
The model was also configured to simulate the measured near-bottom
velocity and suspended sediment profiles collected by Wright (1999) during a
tripod deployment as part of the STRATAFORM Project. The tripod was
deployed in about 12 m water depth off the coast of Virginia over a bed of
poorly sorted sands, silts and clays. Due to the high clay content, we
represented the bed as cohesive sediment in the model simulations. Figure 2
shows a
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