Perform flood simulation analysis

After a simulation has been configured, it must be run. When a simulation is run, an analytical elevation surface is created, using either the currently visible layers or a custom set of layers. Water movement and pooling is calculated and progressively displayed in the view. As the simulation runs, a cache of key moments is built. Playback controls can then be used to replay or step through the results. Change the playback Rate to a lower frames-per-second (fps) value for faster processing, or to a higher rate for smoother display in the view

Run a simulation

Once the simulation layer has been added to the scene and configured, the flood simulation can be run. To do this, click the Run button in the Build group of the Simulation tab. The simulation begins to play.

As the simulation runs, the time currently being displayed is reflected in the Current time box in the Playback group of the Simulation tab. As each calculation is generated, it displays, the current time value updates to match, and a playback cache is built. The time difference between each cached moment is seen in the read-only Step time box.

To move to a specific instant in time within the simulation, type a new time value into the Current time box and press Enter. The simulation loads the nearest previous cached moment and plays forward from that time.

Use cell size

The cell size of a simulation is determined by the size of the area of interest. As the extent of the area of interest increases, the cell size used for the analysis also increases. For example, a 2 kilometer by 2 kilometer extent with a 4096 processing resolution uses a 0.49-meter cell size, while an 8 kilometer by 8 kilometer extent uses a 1.95-meter cell size. A smaller value provides more detailed use of the terrain.

The maximum cell size for a simulation layer is 3.5 meters. This means the extent of the area cannot exceed 3.5 times the maximum processing resolution in length. For example, a simulation layer with a maximum processing resolution of 4096 has a maximum physical size of 4096 x 3.5 m, or 14.3 km. If you try to make it larger, a warning appears and the area is clipped to the maximum value.

Turn off the Maximum Fit button in the Resolution group of the Simulation tab to manually adjust the cell size. By default, this option is on and the cell size is automatically calculated. Click the drop-down gallery to choose a new maximum resolution—the maximum cell size updates. Three maximum resolutions are available:

• 2048
• 4096
• 8192

Use temporal resolution

You can choose the temporal resolution a simulation uses when generated. This controls the number of computations done per simulation second. Click the Temporal drop-down gallery in the Resolution group of the Simulation tab to change the temporal resolution. The available options are as follows:

• Low—A small number of computations per simulation second for the fastest processing speed. Suitable for flat terrain and shallow water depths.
• Moderate—A moderate number of computations per simulation second for a balance of analysis speed and modeling faster water movement. This typically performs approximately four times the number of computations as Low. Suitable for mixed terrain and varying water depths.
• High—A large number of computations per simulation second for modeling fast water movement. This typically performs approximately 20 times the number of computations as Low. Suitable for steep terrain and deeper water depths.

Use terrain level of detail scaling

When a flood simulation scenario is run, the first processing step collects elevation values from the content in the scene. For the ground elevation surface, you can choose which level of terrain level of detail to use during this process.

For the most accurate result, move the Elevation Precision slider in the Resolution group of the Simulation tab to the Precise setting. Depending on your scenario and the scene, this may take longer to run. For the fastest processing time, move the slider to the Fast setting. There are four settings on this slider. The view redraws to show which level of detail of the terrain is being used once the simulation begins.

Tip:

• Use a faster setting for initial investigation and then run the scenario at a more precise setting when finer detailed analysis is required.
• There are slight differences in how water flows and accumulates when you switch between each level of detail scaling step.

Play back a simulation

Once the full duration has been generated and played though once, playback controls can be used to incrementally step through the cached results. These controls include the following:

• Move to Start —Set the simulation to its starting state.
• Step Backward —Move the simulation backward one step.
• Play —Begin animating the cached simulation.

  Note:

  When changes have been made, a red exclamation mark appears next to the Play button to indicate that the cached simulation does not include recent changes. When this icon combination appears, the cached simulation can still be replayed. Click the Run button in the Build group of the Simulation tab to rerun the simulation and capture the updates.

• Step Forward —Move the simulation forward one step.
• Move to End —Set the simulation to its last cached state.
• Rain —Display the 3D visual rain effect while playing the simulation. This is only available in global scene views.
• Playback Frame Rate—The maximum frames per second (fps) used to display the in-progress simulation calculations in the view. Higher frame rates look smoother but can increase the total time needed to complete the calculations. Use a low frame rate to minimize processing time. Rates available are as follows:
  • 1 fps
  • 10 fps—This is the default.
  • 60 fps
  • 144 fps

Note:

You can use the playback controls while the simulation is playing, but the time continues to move forward after you click. To use the step or move controls, it is recommended that you first pause the playback.

Rerunning a simulation

If changes are made to the configuration after it has been run, the simulation must be run again and the cache rebuilt to show the new results.

Note:

Symbology changes do not require the scenario to be run again.

A red exclamation mark appears next to the Play button to indicate that the cached simulation does not include recent changes. When this icon combination appears, the cached simulation can still be replayed. In the Build group of the Simulation tab, click the Run button . The existing cache will be removed and a new simulation cache will be generated capturing the updates.

Clearing a simulation cache

A simulation cache is maintained even when a project is closed. If you do not want to save the cache, click the Clear button in the Build group of the Simulation tab. You can also configure how individual layers manage their cache on the Cache tab of the simulations' Layer Properties dialog box. You can also delete all display caches, including all simulation layer caches, by clicking the Clear cache now button on the Display tab of the project Options dialog box.