Spatial Shallow n

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.

../../../_images/spatia0021.png ../../../_images/image4.png

Sample Data#

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

../../../_images/spatia0031.png ../../../_images/spatia0041.png

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.

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