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structure of the current boundary layer. Morphodynamic change, produced by
gradients in sediment transport rates, alters the waves and currents and their
subsequent driving of sediment transport. Despite these complex and non-linear
relationships, understanding of these processes has grown considerably. If
guided by reliable laboratory and field data, understanding is sufficient to
provide a basis for developing predictive tools.
The numerical circulation model M2D (Militello et al. 2004, and references
therein) developed in the USACE Coastal Inlets Research Program (CIRP) has
proven to be efficient, robust, and reliable for simulating circulation in complex
coastal environments. It provides a solid hydrodynamic foundation for
developing a general-purpose sediment transport and morphodynamic model.
The M3D model is a three-dimensional extension of the M2D depth-averaged
technology.
The M3D model hydrodynamic and sediment transport components were
tested against numerous data sets as part of this study. The model successfully
reproduced the time-dependent flow and suspended sediment transport
measurements in flow tunnel experiments of Ribberink, et al. (1994) and the
flow and suspended sediment vertical profiles and time series data from the field
experiments of Wright (1999).
M3D was applied to simulate in-filling rates at the St. Marys Entrance
channel to test the morphodynamic component and the general applicability of
M3D to coastal problems. The model simulation demonstrated the influence of
water depth and grain size on the calculated sediment transport rates. The
systematic decrease in shoaling rates with distance offshore is correctly
simulated with the model and can be explained by the dependence of bottom
stresses on water depth and the ambient grain size, as discussed below.
2.
M3D Model Description
The M3D model was developed as a CIRP research activity. The basis for the
M3D model development is an explicit merging of M2D and the SLICE
numerical model. SLICE was developed by URS Corp. as part of the Office of
Naval Research (ONR) project STRATAFORM (Nittrouer 1999). SLICE is a
time-dependent, two-dimensional coupled process-based hydrodynamic,
sediment transport, and morphodynamic change model. It represents short to
medium (days to centuries) time-scale evolution of continental shelf
morphology and stratigraphy. SLICE simulates sediment erosion, transport,
deposition, and bed elevation changes for arbitrary initial bed profiles in
response to wave and tidal forcing. The model includes representations of a)
wave-current boundary-larger interaction, b) effects of vertical sediment
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