Spatial Shallow n

Overview

A spatially variable shallow n-value enables the flow roughness to be depth integrated to enable high n-values at shallow flow depths. The value can also be globally assigned in the FLO-2D Control and Tolerance Variables window. Polygons can be applied to select individual or groups of grid elements to supersede the global n-value as in the case for streets and parking lots.

Digitize or Copy Data

1. Select the Shallow-n Areas layer and click edit.

2. Create or copy the polygons that represent the shallow roughness areas to the layer and save them.

Sample Data

1. Click the Sampling Spatial Shallow-n Values button and then OK once the process is complete.

Troubleshooting

1. Create the shallow-n polygons if they are missing from the Shallow-n Areas layer.

2. If the Grid layer is empty, create a grid and try again.

3. If a Python error appears during the sampling process, the attribute table may be missing. Save and reload the project into QGIS and try again.