Roughness Definitions

Roughness definitions are non-visual objects that enable roughness to be defined as a function of depth in the mesh elements of 2D Zones and Roughness Zones The roughness value (Manning's n) in the mesh elements will change dynamically during a simulation according to the roughness definition function.

Up to three roughness (Manning's n) and two depth thresholds parameters can be specified, which will be applied to mesh elements within any 2D Zones and/or Roughness Zones that the Roughness definition is associated with.

If more than one roughness value is specified for the roughness definition, the additional roughness values are set at specific depth thresholds. For roughness definitions with multiple roughness values, the roughness is defined as a smoothed step function where the transition between roughness values follows a cubic spline.

The cubic spline interpolation covers the last 10% of the depth band or 10cm, whatever is higher, capped at the depth band coverage.

A depth band is defined as the difference between depth thresholds, with the last depth band covering all the depths beyond the highest depth threshold.

If the depth band is, for example, 50cm, the cubic spline interpolation could cover 5cm. But as 10cm is higher than 5cm, the spline will actually cover 10cm.

Where there is a roughness definition with, for example, two depth thresholds of 0.1m and 1m, there will be two depth bands one between 0 and 0.1m, and the second depth band between 0.1m and 1m. The cubic transition between roughness values occurs in this example between 0m and 0.1m for the first depth band, and between 0.9m and 1m for the second depth band.

If only one roughness value is specified, no depth varying roughness occurs and the same roughness value will be applied to the mesh elements in the 2D Zone and/or Roughness Zone which is associated with the Roughness definition.

A single Roughness definition object can be associated with one or more 2D Zones and/or Roughness Zones by selecting the name of the relevant roughness definition object from the Roughness definition field in the 2D Zone or Roughness zone tab of the Polygons Grid or on the 2D Zones and/or Roughness Zones Property Sheets.