Iterations of the 2D Model Following the Initial Run

After completing the initial 2D simulation and reviewing overland flow dynamics, the next step is to refine the 2D grid extent. The goal is to optimize the simulation domain—ensuring it accurately captures areas of flooding while maintaining computational efficiency.

Refining Grid Boundaries

During this refinement process, two conditions may arise:

1.     Flooding Extends to the Grid Boundary
If flood depths or pooling are observed along the edge of the 2D grid, it indicates that the boundary may be too tight. In such cases:

• Extend the grid boundary to include adjacent subcatchment areas.
• If flooding appears to extend beyond the subcatchment boundary, you should also consider adding a 2D outfall to allow water to exit the model domain and maintain proper hydrodynamic conditions.

2.     Overly Large Initial Grid
If the initial boundary is excessively large and includes areas that are not contributing to the flooding dynamics, reduce the extent of the grid. This helps optimize computational resources without compromising model accuracy.

Through this iterative process, you can strike a balance between model precision and performance, ensuring the final 2D grid captures relevant flooding behavior without unnecessary computational load.

In this tutorial, both boundary refinement strategies have been implemented. The 2D Boundary Layer was extended where needed to capture surface flooding, and outfall nodes were added to the 2D grid network to prevent artificial ponding at the model boundary. These outfalls were placed at 2D nodes with the lowest elevation near the edges of the study area to ensure proper drainage. Table 2.5 summarizes the properties of the 2D outfalls and associated conduits, while Figure 2.5 shows their spatial locations within the extended boundary.

To improve simulation efficiency, the 2D grid was reduced in areas that do not contribute meaningfully to flood dynamics. This helped optimize model performance without sacrificing result accuracy. The refinement process—including adjustments to the boundary extent and outfall placement—was performed iteratively, following the steps outlined in Steps 2 through 6 of the model setup section.

This combined approach ensures hydraulic continuity, prevents unrealistic surface ponding, and produces flood simulation results accurately reflect real-world conditions.

Table 2.5 : Outfall and Corresponding Conduits Properties

Once these refinements are complete, the 1D-2D integrated flood model is ready for final simulation and analysis. The final schematic of the completed model, including the 2D grid, conduits, and outfalls, is presented in Figure 2.6. This model is then simulated for 2-,10-, and 100-year 24-hour storm events with 0.5 sec routing time step. Be sure to save the model after each simulation is completed.