Land Cover – Surface Roughness

Dynamic simulations of waterflows on a 2D surface, such as in Core+ DynamicFlood, require specification of the surface roughness, in the form of Manning's number M. We specify the roughness of each cell in the model based on the land cover class of the cell. It is possible to use depth-dependent roughness for a land cover class, with parameters y₁, M₁, y₂, M₂, in which case the roughness is M₁ for water depths below y₁, and M₂ for water depths above y₂, with the roughness varying gradually in between y₁ and y₂.

The table below lists the Manning's M values we assign to each class in our land cover map. The values in the table were chosen based on an evaluation and synthesis of relevant literature (Arcement, 1989, Papaioannou et al, 2018, HEC-RAS 2D User's Manual, N-V240 Vannhåndtering, MSB2260).

Note that in Sweden and Germany the default Manning's M values are slightly different, in order to align with national recommendations. See the country-specific section for Sweden and Germany for the values and reference.