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For physical properties of sediment bed, EFDC+ with the erosion rates option 3 uses below input files to configure the initial model conditions for spatially varying physical properties of sediment bed layers, and these files can be created using sediment core datasets by a sediment bed construction tool in EFDC+ Explorer.
sedb.inp: fraction of each sediment class
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where E is erosion rate (cm/s), τb is bed shear stress (N/m2), τcr is critical shear stress (N/m2), and A and n are the fitted parameters based on the SEDFlume core data. With the erosion rates option 3, then, the SEDZLJ algorithm in EFDC+ computes the erosion rates using Equation (1) based on user-defined three erosion rate parameters (A, n, and τcr) and a maximum erosion rate (Emax), which are obtained from the SEDFlume study. The maximum erosion rate is employed for each bed layer in order to prevent the prediction of unrealistically high erosion rates, which might occur due to the exponential formulation of Equation (1) when a high shear stress is applied.
Figure 1 1. Selection of Erosion Rates Option 3: Equation (E = A*Tau^n) and Bed Properties Using SEDB, BEDLAY, BEDBDN, and BEDDDN - General Tab.
The files sedb.inp, bedlay.inp, bedbdn.inp, and bedddn.inp specify the initial conditions for sediment bed in the model, and the user can create those files using a sediment bed construction tool in EFDC+ Explorer. To assign the sediment bed initial conditions, the user may click Assign Bed IC button in the Erosion Rate Options frame in the General tap (Figure 1), then the Initialization of Sediment Beds window will appear as shown in Figure 2.
Two options are available in the Grid Cell Options frame to specify the region for sediment bed initialization:
All Grid Cells: EFDC+ Explorer will initialize all grid cells in the model domain using a single sediment core file
Only Grid Cells Inside Polygons: EFDC+ Explorer will initialize the only grid cells inside the applied polygons using a sediment core file.
In the Initialization of Sediment Beds frame, among three available options (Use Polygon DSM, Use Sediment Core with Grainsize, and Create Uniform Bed), the user needs to select the Use Sediment Core with Grainsize and browse a sediment core file (*.dat) that contains sediment bed sample properties (e.g., sample location, sample depth, layer thickness, porosity, specific gravity, and grain size fractions). The ways to produce the sediment core file (*.dat) and initialize the sediment bed are described in detail at Sediment Bed Construction.
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Figure 2 2. Erosion Rates Option 3 - Initialization of Sediment Beds.
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The Erosion Rate Matrix (cm/s) for Active for Active & Deposited Sediment Bed in the Erosion Rates tab (Figure 3) is used as a lookup table for calculating erosion rates in active & deposited bed layers as a function of their D50 size during the model simulation. The user may see that the first row of this matrix presents the Erosion Multiplier (A), Erosion Exponent (n), and Maximum Erosion Rate (cm/s). To fill this lookup table, the user may utilize the SEDFlume core test results or can adjust them manually for model calibration.
Note: The lookup table for critical shear stresses (τcr) in active & deposited bed layers is specified in the Sediment Bed tap.
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Figure 3 3. Erosion Rates Option 3 - Erosion Rates Tab.
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The sampling location of each SEDFlume core also needs to be entered in Easting (m) and Northing (m) Coordinates for utilizing the Core Assignment features of EFDC+ Explorer.
Figure 4 4. Erosion Rates Option 3 - Core Definitions Tab.
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