Simulation Parameter Configuration

Instructions

The Simulation Parameter Configuration function is used to set parameters that affect the water movement process, including evaporation rate, rainfall rate, participating layers, initial water depth, infiltration parameters, Manning's roughness, and time step.

Function Entry

  • Flood Simulation tab -> Configure Simulation Layer group -> Simulation Parameter Configuration button

Steps

  1. Click the Flood Simulation tab -> Configure Simulation Layer group -> Simulation Parameter Configuration button to open the "Simulation Parameter Configuration" dialog box.
  2. Target Datasource Setting: Select the target datasource to be operated. The simulation parameters will be saved in this datasource.
  3. Evaporation Setting: Set the evaporation rate of water, in mm/h, default value is 0.
  4. The study area is a closed area: Check this option to prevent water from flowing in or out of the study area. Common for simulating waterlogging or closed depressions.
  5. Rainfall Rate Setting: Configure the rainfall amount and its time distribution during the simulation. Complete the settings through the following operations:
    • Add Row: Click the "Add Row" button on the toolbar to add a new row in the list, where you can set the start time (format hh:mm:ss) and rainfall rate.
    • Delete: Select any row in the list and click the "Delete" button on the toolbar to remove it.
    • Import Table: Click the "Import Table" button on the toolbar to open the Import CSV dialog box. Select the target CSV file, then choose the corresponding columns for "Start Time", "Rate", and "Unit" in the file to complete the import.
    • Export Table: Click the "Export Table" button on the toolbar to open the Export CSV dialog box. Set the file name and storage path, then save the current rainfall rate data as a CSV file.
  6. Parameter Layers: Check the layers in the target datasource that participate in the simulation analysis (water channel, water area, water source, obstacles, etc.). All are checked by default.
  7. Initial Water Depth: Set the initial water depth by selecting a raster dataset. Once selected, the initial water depth of each cell is the raster value of the selected raster data at the corresponding position of that cell.
  8. Infiltration Parameter Setting, set via drop-down list:
    • Initial Infiltration Rate (mm/h): The infiltration rate of soil at the initial moment. A higher value indicates stronger infiltration capacity under dry conditions.
    • Saturated Infiltration Rate (mm/h): The stable infiltration rate when the soil is near saturation. This value is smaller than the initial infiltration rate.
    • Infiltration Decay Coefficient (h): The rate at which the infiltration rate decays from the initial value to the saturation value. A larger value means faster decay, causing the soil to reach saturation quickly; a smaller value means slower decay.
  9. Manning's Roughness: A coefficient that reflects the resistance of the ground or riverbed to water flow. A larger value indicates greater resistance and slower flow velocity. Different surface types (e.g., grassland, woodland, built-up areas) correspond to different Manning's roughness values.
  10. Model Parameter Settings:
    • Time Step (s): The time interval corresponding to each calculation step in the model. A smaller time step yields more refined results but requires longer computation time.
    • CFL Number: A stability condition in numerical calculations used to automatically adjust the actual computation step. The value range is [0.0, 10]. A smaller CFL number results in more stable but less efficient calculations. Typically, values between 0.5 and 1 are used to ensure computational stability.
    • Total Simulation Time: The total duration of the model from start to end, i.e., the duration of the flood process to be simulated. The unit can be set via the drop-down menu behind it, including s (seconds), min (minutes), h (hours), and d (days). The default is s.
    • Output Interval (step): Specifies how often simulation results are output. For example, if the output interval is 10, results are saved every 10 time steps.
    • Dry-Wet Boundary Depth (m): The critical water depth for determining whether a cell is in a "dry" or "wet" state. If the water depth is below this value, the cell is considered a dry area and does not participate in flow calculations, improving computational efficiency.
    • Minimum Water Depth (m): The minimum water depth threshold allowed to prevent infinite velocity and computational crashes when the water depth approaches zero. If the water depth of a cell is below this value, it may be ignored or specially handled to avoid abnormal numerical calculations.
  11. After completing the settings, click the OK button to save the simulation parameters in the parameter table dataset.
Notes:
  • The simulation parameters will be saved in the parameter table dataset of the target datasource. Please ensure the target datasource is correctly selected.
  • The time step, CFL number, and output interval affect computational stability, computation time, and result output frequency. It is recommended to set them based on the simulation range and accuracy requirements.

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