The most state-of the-art sediment transport sub-model for EFDC is the SEDZLJ module that uses Sedflume data to determine erosion rates has been developed by Sandia National Laboratories. A detailed description of the SEDZLJ implementation in EFDC code is available in Sandia National Laboratories Environmental Fluid Dynamics Code: Sediment Transport User Manual (Thanh et al. 2008). The SNL approach, shown in Figure 1, accounts for multiple sediment size classes, has a unified treatment of suspended load and bedload, and appropriately replicates bed armoring. The resulting flow, transport, and sediment dynamics in the model is an improvement to previous models because this model directly incorporates site-specific erosion rate and shear stress data, while maintaining a physically consistent, unified treatment of bedload and suspended load.
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The General tab (Figure 3) is used for primary computational options for the SEDZLJ sub-model. Options include allowing bed morphology changes with hydrodynamic feedback, computing bedload for coarser classes, and accounting for bed slope changechanges and applying anti-diffusion to vertical sediment concentrations.
The Date/Time to Start Sediment Transport allows the user to run the model without erosion and deposition active until the model is stable. After model is stable, the sediment transport is fully activated from the specified time. The Deposition Limit of water Column Sediments is a value from 0 to 1. This represents the minimum fraction of sediment in the bottom water layer allowed to deposit in a single time step. Setting this to zero would cause 100% of the amount to be deposited in one time step, however, this is also dependent on the settling rate specified. The Minimum Water Depth for Shear Stress Updates (m) is the minimum water depth of a grid cell that allows calculating the shear stress.
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Hard Bottom Option frame allows user select in which area bed processes are activate or not. (Assign value to 0 for deactivate all bed processes for cell and 1 for allows all bed processes are activate).
Figure 3 SEDZLJ sediment transport sub-model – General tab.
1.2 Sediment
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Properties Tab
The Sediment Properties for Sediment Distribution frame allows the user to set the class size, and critical shear stresses for erosion and deposition for each class. The units are in dynes/cm2 as SEDZLJ data is generally reported in CGS units, so EE maintains these units for consistency with the reported data. It should be noted that the process of erosion and deposition are handled differently in SEDZLJ. The redeposited grain size has a different shear stress.
In the Incipient Motion & Settling Estimates frame the Sediment Information frame shown in Figure 4 there is a Sediment Info button which reports the critical shear stress for grain sizes used in the Sediment Properties for the Sediment Distribution table. These calculations for the critical shear stress are based on the equations from Van Rijn (Van Rijn, et al 1984) which use uniform grain size calculations and provided for the user’s information. These numbers do not have any impact in the actual model calculations. The Initialize Defaults button uses the values calculated here to provide initial values for the critical shear stresses for erosion and deposition, though the user would normally have measured data for these.
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Figure 4 SEDZLJ sediment transport sub-model – Sediment Distribution Properties tab.
1.3 Sediment Bed Tab
In the Sediment Bed tab shown in Figure 5, the Sediment Bed Layering frame allows the user to set the active layer multiplier as well as the layer thickness for all the layers.The Active & Deposited Sediment Characteristics frame allows the users to specify the Number of Deposited Sediment Classes, as well as the Number of Shear Stress Categories to Calculation Erosion of Newly Deposited Sediments and the number of active layer multiplier. Note that SEDZLJ allows for a different number of sediment classes for the sediment distribution and erosion characteristics.
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Bedload Options frame allows user select computing bedload for coarser classes or not and set its parameter settings
Figure 5 SEDZLJ sediment transport sub-model – Sediment Bed tab.
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The Erosion Rates tab provides the user with the Active and Deposited Sediments Erosion matrix as shown in Figure 6. Highlighted Matrix . Which data displayed in this frame depend on the selection of Erosion Rates Options in General tab.
Note: Highlighted cells provide a warning to the user that the erosion rate is not increasing with the increasing shear category, or that erosion rates are not decreasing with the increasing grain size. This is simply a QC check for the user and EFDC+ will still run despite the inconsistent values that have been input.
Figure 6 SEDZLJ sediment transport sub-model – Erosion Rates tab.
1.5 Core Definitions Tab
The Core Definitions tab, shown in Figure 7 6 is where the user defines the Number of SedFlume Cores, and thenassigns the key parameters associated with each core. For example, if the user sets the number sedflume cores to two, then in the Core Parameter frame the drop-down will be populated with two cores. The names name of these are user configurable and will appear each core are set in the information box in ViewPlan when looking at SEDZLJ Options | Core Zone.text box under Sediment Erosion Characteristics frame
For each layer in each core the , user should set the critical shear stress and bulk density . The as well as percentage of the grain size distribution as a percentage also needs to be input in the first table. In the second table the user should input in Bed Layer Properties and Grain Size Distribution frame. In SEDFlume Measured Erosion Rates frame, user should define the initial bed erosion rates for each layer for each shear stress defined.
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, which data is used in this table depend on the selected option of Erosion Rates Options in General tab.
Figure 6 SEDZLJ sediment transport sub-model – Core Definitions tab.
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In the Core Assignments tab shown in Figure 8 7 the user sets the different zones in the model grid for each core type. The DSI standard for this data is just the I, J map, and the core (EFDC looks for DSI in first line). There is a different format for this file for SNL. These file format type is set in the CORE_FIELD.SDF Format frame.
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The Spatially Varying Core Assignment frame provides options for the user to set the appropriate cores to the rest of the model domain. The Use Nearest Neighbor Approach option uses an interpolation method to assign core numbers using the X, Y coordinates of the core.
Figure 8 7 SEDZLJ sediment transport sub-model – Core Assignment tab.
The Assign Core Numbers using Polygons with ID’s option is an ordered assignment based on the IDs in the P2D file. This file is begins with a single line header that is used as the ID of the polyline/polygon, which in this case is the core number. Next in this file comes the X, Y data to define the polygon. EE assigns the specified core number to the group of cells that lie inside the polygon. In some cases polygons may overlap, for example the user may make a polygon with core ID 4, which is inside that for core ID 2. In this case, core ID 4 will have precedence over core ID 2 and core ID 2 will not be used at all
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7 Wave Options Tab
The SEDZLJ wave options can be set by the user to impact the bed shears. The Wave Action Options dropdown provides three options: No Wave Action, Wind Wave (SEDZLJ), and STWAVE. While these options can use the EFDC+ internal wind waves, at this stage they only impact the boundary layer. It is anticipated in the future that SEDZLJ will be updated so that it can use the internal wind waves or external wave linkages in the EFDC wave sub-model, however, at this stage this option is not available.
If the standard SEDZLJ wind wave option is used then the EE wind wave option is not used. In this case the user must ensure they have all the correct files such as FETCH.INP refer to the SEDZLJ user guide for details on this format. Conversely, if the STWAVE option is selected then that correctly formatted STWAVE files are required.
Figure 9 8 SEDZLJ sediment transport sub-model – Wave Options tab.
1.9 Miscellaneous Tab
Miscellaneous tab is shown in Figure 8. In this section, user can set Skin Friction Options and select use constant bed shear stress or not. The user should refer to the SEDZLJ user manual for more information on Skin Friction Options and Use Constant Bed Shear Stress options.
Under Class Maximum Grain Size frame, the table shows the maximum grain size of each sediment class from input data.
Figure 8 SEDZLJ sediment transport sub-model – Miscellaneous tab.