Build a 2D Lake Model (Level 1 Step-by-Step Guidance)
- Duy Pham
- Kester Scandrett
- Linh Nguyen
1 Introduction
This tutorial will guide the user on how to set up a 2D lake hydrodynamic model and run a solution for EFDC. It will cover the preparation of the necessary input files for the EFDC model and the visualization of the output by using the EFDC+ Explorer (EE) Software.
The data used for this tutorial are from Hillsborough Water Atlas, Lake Thonotasassa, Florida, USA. All files for this tutorial are contained in the Demonstration Models of the Resources page folder file (DM-14_Lake_T_HYD-WQ_Model). Note that the model grid will contain more than 300 grid cells and use the dye module; therefore, a Demo version of EE, which only allows running models with less than 300 horizontal cells and without the dye, salinity, and particle tracking modules, will not be applicable. The user, however, can load and view the model without being able to edit, save edits, run, and view model output with this version.
Before beginning the first session, let's introduce the main form of the EE GUI to help you better understand our explanations in this document. Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 1 is the main form of EFDC+ Explorer or EE User Interface.
2 Create a New Grid
This session will guide you to create a new simple grid with EFDC+ Explorer.
Lake Thonotosassa is located in Hillsborough County, Florida, USA, and has been chosen as an example of where to build a 2D model in EE
The gird generation process includes the following steps:
1. Open EE
2. Click New Model icon: on the main menu of the EE interface. The Cartesian Grid Generator frame appears in Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 2
3. In Grid Options, select Uniform Grid.
4. Click Set button to select projection as UTM Zone 17 in the northern hemisphere, as the lake is located in that zone (Figure 2.1)
4. RMC (Right Mouse Click) on the Bounding Polygons blank to open a pop-up menu. In the pop-up menu, select Add Files to browse the polygon file. The land boundary of the lake will be loaded here.
The polygon file for this model is "Outline.p2d" and can be found in Data/Bathymetry folder of the Demonstration Models provided above.
5. With the polygon file loaded, the X-Y Directions for the corners of the models are automatically defined. The user can also adjust the Cell Size and Number of Cells in Uniform Grid Options.
In this example, enter cell size is 100x100m for the Cell Size (m) then click the calculator symbol for the Number of Cells.
6. If the user adjust any options in Uniform Grid Options they must click the Generate button so that EE can generate the changes.
7. Click on Remove Dry, this will remove all cells outside of the polygon.
8. Click OK button to finish grid generation. An overview of the created grid is shown in the General tab (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 5).
9. Save the model by selecting the Save button and create a new directory.
3 Assigning the Initial Conditions
This section will guide you on how to assign the initial conditions, such as the bathymetry, water level, and bottom roughness.
3.1 Assigning the Initial Bathymetry
1. Select the Initial Conditions tab and right mouse click (RMC) on the Bathymetry sub-tab. A new Bathymetry form will appear. In that form, click on Assign to define bathymetric value.
2. The area the user wants to assign the bathymetry data to is set by a poly file. In this case, choose All grid cells
3. The data for bathymetry values are assigned by “Bathymetry.dat” file in Bathymetry folder . This bathymetry file is simply an xyz format.
4. Choose Scatter (XYZ) data and then Add file to browse for “Bathymetry.dat”.
5. After adding the data file, click on the Apply Defined Conditions button to make your changes take effect before selecting the OK button.
3.2 Assigning the Depth/Water Surface Elevations
This step assigns the initial depth or water surface elevations. There are two options for setting the surface water elevation, namely, use Constant and use Scatter (XYZ) data.
1. RMC on Water Depth/Elevation button then click Assign Elevation button (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 10)
2. Select Constant to assign a constant water surface elevation of 11.5 m in the Constant box. (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 11).
3. After selecting this option for assigning water surface elevation, click Apply Defined Conditions button, then click the OK button to finish.
4 Boundary Conditions
This section will teach you how to prepare and assign the boundary conditions to the model cell configuration. In this Lake 2D case, there are two flow boundaries; one is runoff inflow to the lake, and the other is outflow through a gate. Thus, we should prepare two-time series of inflow and outflow boundaries. In other cases, the number of time series for boundary conditions might be much more, such as those for hydraulic structures, pressure boundaries, or include time series for temperature, salinity, and water quality boundaries.
4.1 Set Time Series
To set the boundary time series, take the following steps:
1. Select the External Forcing Data tab. (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 12)
2. RMC on Flow button and select Add New Data Series to edit the flow boundary. (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 13)
3. Enter the Number of Series into the box. There are two flow boundaries as mentioned so it should be “2”.
4. Give a Series Name for associated time series. In this case, title “Inflow” for Series 1, and “Outflow” for Series 2. (remember to press Enter after each input)
5. To import Inflow time-series data, click on the Import data from file button on the Toolbar.
In the ASCII Data Import form as shown in Figure 4-2.
(1) Browse to the “Inflow.dat” file and select the data format as EE Dat or WQ Data.
(2) Modify the Import Settings parameters as Figure 4-2 shows.
• Header Rows to Skip: 0
• Data Base Date: 1/1/2012
• Import from Data Column: 2
• Conversion Factor: 1
(3) Click OK to import the data series; the Import Data form will appear to select import options.
(4) Click OK in the Import Data window to close the form and finish importing data (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 13).
(5) Save the model
6. Click to the View Time series plot icon to view the current time series.
7. Select the up/down arrow buttons to edit the other time series.
8. Repeat Step 5 to import “Outflow.dat" to the model (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 16). The time series plot of outflow is shown in Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 17.
9. Click OK to finish editing the boundary time series.
After completing the above steps, the user has prepared all the required boundary time series. Now, we will assign these boundary time series to the model cells. Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 18 shows the location of inflow and outflow for this lake case. Thus, we have to assign these cells with associated time series for in/outflow prepared in the previous session.
4.2 Assigning a Boundary Condition
In order to assign the boundary, the following steps should be taken;
1. Click the 2DH View icon on the main form of EE (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 1).
2. Choose Boundaries in the Viewing Layer Control .
3. Enable Edit grid by turning on the icon (see Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 19)
4. RMC on the inflow location cell and select Add New Boundary Group (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 20)
5. Enter the Boundary Group Name by typing “Inflow” and select boundary types (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 21). Then click OK button, the Flow Boundary Conditions form appears in the Forcing Assignment frame, select "Inflow" for Flow Table (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 22), then click OK button.
If there are more than one Boundary Cells, the user must click on All to select all boundary cells then click on Dist Factors to distribute the factor to all boundary cells. The sum of Factor for all boundary cells must equal 1.
6. Apply the same process for assigning the outflow boundary cell. Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 23 presents the boundary conditions after assigning the inflow and outflow boundaries.
5 Model Timing
After completing the previous sections, the user has almost completed the hydrodynamic model of a lake. This section will guide the user on how to set up the model simulation time and model time steps.
1. Select Timing/ Linkage tab and RMC on Timing button
2. Enter the duration of start/ end of the simulation. Note that the boundaries time series should always cover this simulation duration period. Otherwise, the model will not run.
3. Enter the Time of Start, Number of Reference Periods, Duration of Reference Periods and Time Step as Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 24. These values are explained in the Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Table 1.
Terms | Description |
|---|---|
Reference Date/Time | The base date of all data and the simulation period. |
Start Date/Time | The model starts the simulation at that time. |
End Date/Time | The model stops the simulation at that time. |
Time of Start (Days) | Number of Julian days after the base date at which to start the simulation. |
Number of Reference Periods | Total simulation time as a multiple of reference periods. |
Duration of Reference Period (hours) | The reference period is usually 24 hours; however, it can be set to another value if required. |
Time Step (seconds) | Also called Delta T, the EFDC model simulation time step. |
Safety Factor | 0 is a fixed time step. Set 0< safety factor <1 to activate the dynamic time step feature. |
# Ramp-Up Loops | Number of initial iterations to hold the time step to a constant during ramp-up. |
Maximum dH/dT | If >0, it is an additional criteria for determining the dynamic time step. |
Growth Step | The minimum number of iterations for each time step before increasing the time step for the dynamic time stepping |
Maximum Time Step | This is a maximum-time step |
4. RMC on Linkage button and set Link EFDC Results to EFDC+ Explorer and set Linkage Output Frequency to 60 minutes. EFDC will record the output every 60 minutes to display the model results in the EE. (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 25). Note that a smaller output frequency will create a larger output file.
6 Hydrodynamic Model Setup
This section will guide the user on how to set the hydrodynamic model for the EFDC model’s application of the wet and dry conditions to optimize the simulation time. For this condition, we should make the following settings:
1. Select Modules tab then LMC on plus sign of Hydrodynamics to expand all sub-tabs. RMC on each sub-tab to adjust settings.
2. Select Shallow Water then RMC, the form of Shallow Water Options appears
3. Enter values for the Dry Depth and the Wet Depth. Then click OK button. Note that the wet depth should always be greater than the dry depth. (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 26).
4. Return to select Model Grid tab, RMC on Grid sub-tab and enter the number of vertical layers required into the box. In this case, we will set the vertical layers equal to 5 (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 27). Click OK button.
5. Save the model.
7 Running EFDC+
This section runs the EFDC model and includes the following steps:
1. Click the Run EFDC icon on the main form
2. Select the Browse iconnext to the Executable text box to browse to the EFDC executable file (Figure 29) as default, the EFDC+ executable file is located in the EEMS installation folder (e.g. C:\Program Files\DSI\EEMS10.3)
3. To save time when running the model, the user can increase the number of OMP threads.
3. Click the Run EFDC+ button to run the model (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 29).
If all settings are correct, the model will start running, and you will see the MS-DOS Window appear showing the model results as shown in Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 30.
You can check the model results while the simulation is running by loading the model or clicking the refresh the model output button.
8 Visualizing the EFDC Model Output
This session will teach you how to view the model simulation results. Once the model simulation is completed, click the Refresh Output button in the toolbar to load the model outputs. These three icons on EE’s main form (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 1) are used to view the model simulation results in 2DH View, 2DV View or 3D View, respectively.
1. Select the 2DH View icon
2. In View Layer Control, select Add a New EFDC View Layer (Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 31). The user should see View Options window with Primary Group and Parameter to display.
3. Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 32 is an example of showing the vector and magnitude velocity field results. Similarly, the user can select other parameters to show the model results.
4. Right mouse-click on the Velocity vector layer to modify the vector arrow sample or change the vector color and scale factor (See Build a 2D Lake Model (Level 1 Step-by-Step Guidance)#Figure 32)
