Sediment Bed Construction
There are several ways to build sediment beds in EFDC+ Explorer as shown in the Initialization of Sediment Beds form in Figure 1. The simplest option is to create a uniform bed, other options include Use Polygon Digital Surface Model and Use a Sediment Cores with Grainsize, each of which is described below. For each of these options the Grid Cells Options frame allows the user to build sediment beds for the whole domain or just for cells inside user-selected polygons.
Figure 1. Initialization of sediment beds.
Uniform Layers
To set up a simple horizontally uniform sediment bed for the model the user can use the with Inorganic Sediment Bed Constructor: Uniform Layers tool shown in Figure 2. This tool is accessed from the Create Uniform Bed button in the Initialization of Sediment Beds. The Bed Constructor asks the user input the number of layers, the number and types of sediments, and allows the user to specify the sediment fractions, thickness, and bulk densities for each layer. The user must still set the cohesive and non-cohesive erosion, and deposition parameters, but once the user finishes this option, the sediment bed configuration is ready for EFDC.
In the Bed Layer Settings frame the user may specify the number of bed layers and subsequently the thickness, porosity (thus void ratio) and mass distribution by layer. Once the sediment bed is generated the user can modify the sediment bed properties in 2DH View, as needed. The layer configuration settings can be saved and later retrieved using the Save and the Load buttons in the Bed Properties Definitions frame.
Figure 2. Uniform sediment bed generation tool.
It is generally expected that creating a sediment bed is done in the early phases of generating a sediment model. EE will attempt to update the parameters in the Morphology & Consolidation tab such as the deposition porosity and cohesive void ratio to match the data entered in the Bed Constructor. This is not a bug and is behaving as expected.
Also, note that the Inorganic Sediment Bed Constructor: Uniform Layer tool adds two layers of "empty" sediment layers to allow for deposition and layer addition. The Maximum Layer Thickness setting in the Morphology & Consolidation tab controls when EFDC will create a new layer during deposition. If the top layer is already activated and the thickness exceeds the maximum layer thickness, EFDC will just keep adding sediment to the top layer. This can result in a very thick layer, which is not a code problem but a model configuration problem and should be avoided. This is expected behavior and is not a bug.
Digital Sediment Model
A very useful feature in EFDC+ Explorer is its ability to build the EFDC sediment files from a defined digital sediment model (DSM) that was generated by some third-party package (e.g., Spatial Explorer). This option is available from the Sediments tab | Modify button | Initial Conditions tab | Initialization of Sediment Bed form and selecting Use Polygon DSM. The DSM format requires a polygon followed by the layer thickness, bulk density, porosity, and grain size distribution for each depth available (sediment depth intervals are based on data). More information on the data structure is available in Appendix B - Data Formats. EFDC+ Explorer uses the DSM coupled with the number of size classes requested, the maximum size for each class, the number of sediment layers, and the layer options (e.g., minimum layer thickness) to build the EFDC sediment files. The "Max (μm)" sediment diameters, one for each sediment class, are needed to break the sediment grainsize curves into ranges. These diameters are not class diameters but represent the grain size breakpoints whose geometric mean of the upper and lower limits is the corresponding sediment class' diameter.
When the user clicks on the Apply button after all the inputs have been provided, EFDC+ Explorer generates the sediment map in memory and then writes out the files. The current sediment map (if any) will be replaced by the new one. It is recommended that the project be saved into a new sub-directory prior to implementing this option in order to save different versions of the sediment bed configurations.
Sediment Cores with Grainsize Option
Another option provided in EE is the ability to build a sediment bed from sediment core data. Figure 3 shows an example of a digital sediment model derived from sediment cores. The data contained grain size distributions by depth interval. The black solid circle symbols show the locations of the cores. The plot shows the resulting depth-averaged d50 grainsize.
The user also has many options for editing sediment cores within the 2DH View window.
How to build a sediment bed from sediment core data is described detail in Sediment Bed Initialization Tools.
Figure 3. A digital sediment model generated from sediment cores with grain size.