Application Of The Model To The Laboratory Data

The result from the deposition experiment with the highest bed shear stress of 0.324 Pa (Test No 1) was chosen for calibrating the model. The other two tests with bed shear stresses of 0.213 Pa (Test No 2) and 0.121 Pa (Test No 3) were used as verification tests. The input parameters for the settling stage of the model include, settling velocity of the sediment flocs, the turbulent diffusion coefficient, and deposition and erosion fluxes of the sediment at the sediment water interface. For the flocculation stage, additional input parameters needed are: (a) the collision efficiency parameter; (b) the collision frequency functions; and (c) a model for the growth-limiting effect of turbulence. A discussion of the various input parameters and their assigned values are given in the following section.

8.5.1 Input Parameters

8.5.1.1 Settling Velocity of the Flocs, w^

Settling velocity of the flocs is calculated in the model using the Stokes' Law and a size dependent density relationship developed by Lau and Krishnappan.21 Accordingly, the expression for the settling velocity becomes:

where wk is the settling velocity of the kth fraction and dk is the size of the sediment floc. The parameters a and b are empirical coefficients that need to be determined as part of the calibration process.

8.5.1.2 Turbulent Diffusion Coefficient, D

The turbulent diffusion coefficient, D was assumed to be equal to the momentum diffusivity, which was obtained by simulating the flow characteristics of the rotating flume using the PHOENICS model.22 The PHOENICS model is a three-dimensional turbulent flow model and it employs the k - £ turbulence model to close the system of equations. A depth averaged value of D was calculated from the three-dimensional prediction of the turbulent eddy viscosity.

8.5.1.3 Deposition Flux, Fd

Deposition flux at the sediment water interface was calculated using the Krone's equation as follows:

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