A Numerical Simulation of the Dispersion of Sediments Suspended by Estuarine Dredging Operations
A predictive numerical model designed to simulate the dispersion of sediments suspended by estuarine clam-shell dredging operations is described. The model evaluates the downstream distribution of the column of materials introduced by each vertical pass of the dredge bucket using a modified conservation of mass approach in which a horizontal moment term is used to represent the spatial distribution of the suspended mass concentrations. Solution of the resultant equation in finite difference form provides a time history of the 0th to 4th moments of the dispersing mass introduced by each bucket pass. A representation of the sum total effect of these discrete injections forming the downstream plume is then developed through linear superposition. This scheme provides a description of the gross characteristics of the dispersing mass without requiring large amounts of computer time and storage.
Required inputs to the model include specification of the local mean velocity characteristics, sediment settling velocities and turbulent mass diffusion coefficients. Field data obtained under a variety of conditions are used to supply these inputs and to test the accuracy of the computational scheme.
Preliminary comparisons suggest that this model provides a reasonable analogue of observed field conditions. Accuracy appears to be primarily dependent on the specification of settling velocity and mass diffusivity representing second-order influences.
KeywordsSettling Velocity Suspended Material Open Channel Flow Clam Shell Finite Difference Form
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