In the General tab, under Erosion Rate Options the user should select the second option as shown in Figure 1. Using this option the erosion rate will be based on the equation E = A*Tau^N where "A" is the erosion multiplier, and "N" is erosion exponent, and it uses bed properties by Core ID. "A" and "N" will be defined in the Erosion Rates tab as shown in Figure 2. Moreover, the user can define the maximum erosion rate of each grain size.
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Figure 1 Erosion Rates Option 2 - General tab.
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Users may select Equation (E = A*Tau^N ) and Bed Properties by Core ID for the erosion rates option in the General tab, if SEDFlume datasets provide the measurements of erosion rates (cm/s) as a function of applied shear stress (dynes/cm2) and the relationship between erosion rates and shear stress can be defined using Jones and Lick (2001)’s approach as:
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 2, 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 Selection of Erosion Rates Option 2: Equation (E = A*Tau^N ) and Bed Properties by Core ID - General Tab.
The Active and Deposited Sediments Erosion Matrix in the Erosion Rates tab (Figure 4) is used as a lookup table for calculating erosion rates in active & deposition 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 & deposition bed layers is specified in the Sediment Bed tap.
Figure 2 Erosion Rates Option 2 - Erosion Rates tabTab.
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After completing the Erosion Rates tab, the users may enter the SEDFlume core datasets to the Core Definitions tab (Figure 3), which would be used for defining the
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physical and erosion properties of parent-bed layers in a model.
The user may enter the Number of SEDFlume Cores and then assign the measurements for physical and erosion properties associated with each core. For example, if the SEDFlume data consists of the measurements for three sediment cores, the user can set the Number of SEDFlume Cores three, then the drop-down will be populated with three cores in the Sediment Erosion Characteristics frame. The name of each core in the drop-down box can be modified by the user manually.
Water Density can be specified as 1 g/cm3, and Sediment Density can usually be determined as 2.65 g/cm3.
In Bed Layer Properties and Grain Size Distribution
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frame, the user can enter the physical properties of each SEDFlume core such as critical shear stress (dynes/cm2), dry bulk density (g/cm3), layer thickness (cm), and grain size fractions (%) for each layer.
In SEDFlume Measured Erosion Rates matrix, the user may enter the erosion properties measured from each SEDFlume core such as Erosion Multiplier (A), Erosion Exponent (N), and Maximum Erosion Rate (cm/s) for each vertical layer.
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 3 Erosion Rates Option 2 - Core Definitions tabTab.