Use rasters to define depth, infiltration, and surface roughness

You can use a raster to define the starting water level depth of a flood simulation as well as the infiltration rate, maximum infiltration values, and surface roughness. Any single-band raster with numeric values, in a supported unit, added to the scene can be used.

Tip:

Raster functions can be used to create a layer in the map in a supported unit without requiring data conversion.

Define the starting water level using a raster

Use a raster to define the starting water level depth. This adds water on top of the area of interest before the simulation begins and is helpful when a scenario should start in a partially flooded state. For example, you can model a dam or a river that is already close to capacity.

To establish the starting water depth, complete the following steps:

1. Right-click the layer in the Contents pane and click Configuration . Alternatively, click the launcher button in the Configuration group of the Simulation tab.

   The Configure Simulation pane appears, loaded with the current parameters.

2. Under the Starting Water Level header, expand the Water Depth Raster gallery.

   All rasters in the Contents pane are listed.

3. Select the raster that contains the starting water level definition.
4. Select the unit of the raster, such as yards (yd), from the drop-down list.

   Note:

   Only millimeters (mm), centimeters (cm), meters (m), inches (in), feet (ft), and yards (yd) are supported.

5. Click Apply to save these changes.

Define the infiltration rate using a raster

Use a raster to define how fast water enters the ground. This provides a more accurate representation of how some water will infiltrate into the ground.

To include an infiltration rate in a flood simulation, complete the following steps:

1. Right-click the layer in the Contents pane and click Configuration . Alternatively, click the launcher button in the Configuration group of the Simulation tab.

   The Configure Simulation pane appears, loaded with the current parameters.

2. Under the Infiltration Rasters header, expand the Infiltration Rate (units/hr) gallery.

   All rasters in the Contents pane are listed.

3. Select the raster that contains the infiltration rate definition.
4. Select the measurement unit of the raster from the drop-down list.

   Note:

   Only millimeters (mm) and inches (in) are supported.

5. Click Apply to save these changes.

Define maximum infiltration using a raster

Use a raster to define the maximum allowable infiltration level. This defines at what point the soil can no longer absorb water.

To include a maximum infiltration rate in a flood simulation, complete the following:

1. Right-click the layer in the Contents pane and click Configuration . Alternatively, click the launcher button in the Configuration group of the Simulation tab.

   The Configure Simulation pane appears, loaded with the current parameters.

2. Under the Infiltration Rasters header, expand the Maximum Infiltration gallery.

   All rasters in the Contents pane are listed.

3. Select the raster that contains the maximum infiltration definition.
4. Select the measurement unit of the raster from the drop-down list.

   Note:

   Only millimeters (mm) and inches (in) are supported.

5. Click Apply to save these changes.

Define surface roughness using a raster

Use a raster to define the surface roughness, which impacts how fast water moves across the area of interest. This allows water to move faster over smooth, or low rough, surfaces—such as roads and parking lots—and highly rough natural surface areas—such as thick vegetation and rocky outcrops.

To include surface roughness rate in a flood simulation, complete the following steps:

1. Right-click the layer in the Contents pane and click Configuration . Alternatively, click the launcher button in the Configuration group of the Simulation tab.

   The Configure Simulation pane appears, loaded with the current parameters.

2. Under the Surface Roughness Raster header, expand the Surface Roughness Value gallery.

   All rasters in the Contents pane are listed.

3. Select the raster that contains the surface roughness definition.

   Note:

   Cell values for the raster should be based on Manning's roughness coefficient, also known as Manning's n, a coefficient which represents the roughness, or friction, that is applied to water flow when estimating water speed. Example values are included in the Surface Roughness Value drop-down gallery.

   Dive-in:

   Manning's roughness coefficient is a way to estimate the impact of the surface on the average velocity of water in an open channel. Robert Manning compiled the formula by comparing and evaluating the best known formulas of the time and presented it in a paper titled On the Flow of Water in Open Channels and Pipes, which was published in 1891 (Transactions of the Institution of Civil Engineers of Ireland, p.173-XXX). This formula remains to this day the standard for calculating the impact surface roughness has on the flow of water.

4. Click Apply to save these changes.