SEDZLJ Sediment Model
The SEDZLJ approach is the most state-of the-art algorithm for sediment transport computations of EFDC. This algorithm has been developed by Sandia National Laboratories, and 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 SEDZLJ algorithm is now considered as the EPA’s preferred standard approach for modeling sediment transport processes in contaminated river sites.
The primary purpose of using SEDZLJ approach is to simulate better the transport behaviors of sediment materials that are typically complex mixtures of different sized-sediment particles. This algorithm uses a unified treatment for multiple sediment classes with representative particle sizes (regardless of cohesiveness) when simulating the movements of sediments in the water column, changes in sediment bed properties, and sediment flux between the water column and sediment bed (i.e., erosion and/or deposition) based on flow fields computed by the hydrodynamic module (Figure 1). In addition, the SEDZLJ approach can employ site-specific erosion rate data obtained from SEDFlume core tests, which measure the thickness change of sediment bed (mixture) as a function of bed depth and applied shear stress in a controlled flume experiment. A detailed description of SEDFlume analysis is available in Jones and Lick (2001).
Figure 1 SEDZLJ Module Framework.
EFDC+ employs a standard format for SEDZLJ input files, which was originally established by Earl Hayter of USACE, and EFDC+ Explorer generates the SEDZLJ input files for EFDC+ simulation run following the standard SEDZLJ input format. Examples of the standard SEDZLJ input files are described in Appendix B 21-24, and three primary EFDC+/SEDZLJ input files are as below:
bed.sdf General SEDZLJ setup, sediment properties, erosion properties for active and deposition bed layers
erate.sdf Erosion properties for parent-bed layers, which were acquired from SEDFlume core tests
core_field.sdf Linkage of SEDFlume erosion properties to model grid cells
EFDC+ Explorer is also capable of loading existing EFDC/SEDZLJ input files created by other agencies with different file formats. Specifically, the SEDZLJ approach has widely been used by several water modeling associated agencies including SNL, USACE, and AnchorQEA, but their input file formats tend to be slightly different from the DSI standard format as they are using their own source code. To retain compatibility, EFDC+ Explorer is designated to load most of those existing SEDZLJ model files and convert them to run in EFDC+.
Users can activate the SEDZLJ sediment transport module by checking the box Sediment Transport in the EFDC+ Modules tab and selecting SEDZLJ in the drop-list.Then the Sediment Transport sub-tab will appear under the Modules tab as shown in Figure 2.
Figure 2 Selection of SEDZLJ Sediment Transport Module.
Major Settings
Users can open the SEDZLJ Sediment and Bed Properties setting window by RMC on the Sediment sub-tab under Modules tab and select Setting. In Major Settings (shown in Figure 3), users may specify the number of sediment bed layers and the number of sediment classes. However, the users should practice a caution when changing the numbers in Major Settings because it may cause loss of existing initial conditions and boundary conditions.
Figure 3 SEDZLJ Sediment Transport Module – Major Settings.
General Tab
In General tab (shown in Figure 4), users can determine primary computational options for the SEDZLJ sub-model (Figure 3) such as allowing bed morphology changes with hydrodynamic feedback, accounting for bed slope changes in erosion rate calculations, and applying anti-diffusion to vertical sediment concentrations.
Date/Time to Start Sediment Transport (days) allows the users to specify the Julian date to start activating sediment transport simulation for erosion and deposition processes (sediment flux between water column and sediment bed). With this function, the user can apply spin-up period to run the model simulation without erosion and deposition processes until the simulated hydrodynamic flow field becomes stable.
Deposition Limit of Water Column Sediments can be determined between zero and one, and this parameter represents the minimum fraction of sediment in the bottom water column layer allowed to deposit in a single time step. Setting this value 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.
Maximum Deposition Layer Thickness (m) determines the maximum thickness limitation for sediment bed layers that receive the deposited sediments during simulation.
Minimum Water Depth for Shear Stress Updates (m) is the minimum water depth of a grid cell that allows calculating the shear stress.
Sediment Timestep (s) is for determining the time step size for computing sediment transport process during the simulation.
Erosion Rate Options frame provides three options for erosion rate matrix data type. Each option requires different types of erosion rate information, so the users need to select one of those three available options considering the data type they obtained from SEDFlume core tests. Details for each option are described in sections: Erosion Rates Option 1, Erosion Rates Option 2, and Erosion Rates Option 3.
Temporally Varying Erosion Rate Parameters frame is an alternative option to use an erosion rate matrix from an external file (ASCII or binary format files).
Hard Bottom Option allows the user to specify in which cell erosion or deposition processes are activated or not. For example, no interaction between sediment bed and water column can occur at deactivated cells where zero value is assigned (bedmap.inp), so suspended sediment load is advected during the simulation but the particles in suspension are not allowed to settle down on riverbed in such deactivated areas. On the other hand, erosion or deposition processes are fully simulated at activated cells where a value of one is assigned (bedmap.inp).
Figure 4 SEDZLJ Sediment Transport Module – General Tab.
Sediment Properties Tab
In this tab, Sediment Class Properties frame (Figure 5) allows the users to set the representative particle size, critical shear stresses for erosion and suspension, and settling velocity for each sediment class. These transport parameters are used to simulate the behaviors of the sediments in active movements (sediment materials in water column layers and active sediment bed layer). As SEDFlume test data are generally reported in CGS units, EFDC+ Explorer also employs the unit of dynes/cm2 for critical shear stresses to be consistent with the reported data.
In Sediment Information frame, there is Sediment Info button reports the critical shear stresses and settling velocities computed based on the particle sizes entered in the Sediment Class Properties table. The critical shear stresses and settling velocities are calculated using Van Rijn’s equations (Van Rijn, et al 1984), and the resulting values are provided in the pop-up window. However, those values are calculated only to provide users a guideline for those transport parameters, and EFDC+ Explorer would not use the values in the pop-up window when generating the SEDZLJ model input file (bed.sdf).
If users click the Initialize Defaults button, the critical shear stresses and the settling velocities in the Sediment Class Properties table will be filled automatically with the values calculated using Van Rijn’s equations. Then, those imported values will be written in the model input file and used for the model simulation. The users may enter those values manually using the associated measurement data they have, or they can also adjust them for model calibration.
Figure 5 SEDZLJ Sediment Transport Module – Sediment Properties Tab.
Sediment Bed Tab
In Sediment Bed tab (Figure 6), users can specify the sediment properties for Active & Deposition Sediment Bed Layers including Active Layer Thickness Multiplier, Number of Sediment Size Categories, Number of Shear Stress Categories to Calculate Erosion Rates (only for Erosion Rates Option 1), and Bedload Options.
At Sediment Erosion Characteristics table, the users can specify the lookup table to determine critical shear stress for active and deposited layers as a function of their D50 size.
Bedload Options allow the users to activate bedload computation for coarser classes and set the cutoff grainsize for the bedload computation.
Figure 6 SEDZLJ Sediment Transport Module – Sediment Bed Tab.
Erosion Rates Tab
In Erosion Rates tab ( shown in Figure 7), users can specify the Active and Deposited Sediments Erosion Matrix, which is the lookup table that determines erosion properties for active & deposition bed layers as a function of their D50 size. The matrix format displayed in this frame varies depending on the Erosion Rates Options selected in General tab, and detail descriptions for each option are described in sections: Erosion Rates Option 1, Erosion Rates Option 2, and Erosion Rates Option 3.
Figure 7 SEDZLJ Sediment Transport Module – Erosion Rates Tab.
Core Definitions Tab
In Core Definitions tab (Figure 8), users can enter several erosion rate datasets acquired from SEDFlume core tests, which will be used to define site spatially varying erosion properties of parent-bed layers.
The users can set the Number of SEDFlume Cores and then assign the key measurements for erosion rate properties associated with each core. For example, if the Number of SEDFlume Cores is set to three, the drop-down will be populated with three cores in the Sediment Bed Characteristics frame where the name of each core can also be modified by users.
In Bed Layer Properties and Grain Size Distribution frame, the user should enter critical shear stress, dry bulk density, layer thickness, and grain size fractions measured from each vertical layer of each SEDFlume core.
The matrix for SEDFlume Measured Erosion Rates can have different formats depending on the Erosion Rates Options selected in General tab, and detail descriptions for each option are described in sections: Erosion Rates Option 1, Erosion Rates Option 2, and Erosion Rates Option 3.
Figure 8 SEDZLJ Sediment Transport Module – Core Definitions Tab.
Core Assignments Tab
Core Assignments tab (Figure 9) helps users to assign the SEDFlume core definitions for physical and erosion properties to model grid cells. This process is to define the horizontal distribution the SEDFlume properties over the model domain.
The users may check the box for Allow Core Definitions on a Cell by Cell Basis and can set the Default Core Number so that EFDC+ Explorer assigns the default core definition to the cells which fall outside the SEDFLume data available region.
With using the Nearest Neighbor Approach option, SEDFlume core definitions will be allocated to the cells based on their locations (X, Y coordinates).
With using the Assign Core Numbers using Polygons with ID’s option, the users can assign the SEDFlume core definitions to the cells within the area specified as a polygon using a P2D file. The P2D file begins with a single line header for SEDFlume core ID, and the following lines present the X and Y coordinates to define the corresponding polygon area. EFDC+ Explorer will assign the specified core definitions to the group of cells that are located inside the polygon.
Through this process, EFDC+ Explorer will generate the associated input file (core_field.sdf) following either DSI Standard format (I, J, and Core Number) or Sandia Lab Standard format.
Figure 9 SEDZLJ Sediment Transport Module – Core Assignment Tab.
Wave Options Tab
The SEDZLJ wave options can be set by the user to impact the bed shears (Figure 10). 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 selected, 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 correctly formatted STWAVE files are required.
Figure 10 SEDZLJ Sediment Transport Module – Wave Options Tab.
Miscellaneous Tab
In Miscellaneous tab (Figure 11), users can set Skin Friction Options and select to use constant bed shear stress or not. The users 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, users can set the maximum grain size for each sediment class that is used in the model. However, the user-defined maximum grain sizes are used only for computing median grain size, D50 (the SEDZLJ model simulation computes the sediment transport process using the representative particle size of each class).
Figure 11 SEDZLJ Sediment Transport Module – Miscellaneous Tab.