Roughness

A Flood Modeller 2D simulation requires a roughness value(s).

You can define roughness values across your model extent either as a single ‘global’ roughness coefficient applied everywhere or as spatially varying roughness values defined by a ‘Roughness File’.

The roughness file can take the form of a raster grid (.ASC file) with roughness values specified in each grid cell.
Alternatively you can reference an OS MasterMap roughness shapefile. When an OS MasterMap roughness file is used you must also create a lookup table (.fric file) to cross reference all MasterMap “DescGroup” field values to equivalent roughness values. In addition to defining your roughness data, an associated "Roughness Law” must be specified; either "Manning” or "Chezy” (default "Manning”).

The lookup table must feature all possible values of the 'DescGroup' field required.
Data from the lookup table is read in using fixed field formatting. The first column is the value of the 'DescGroup' field and is fixed at 40 columns. The next column is the Manning's n value.

An example is provided below: