Variable 2D roughness at low depths
When applying direct rainfall onto 2D zones traditional roughness values do not typically apply, especially where the depths of water on the mesh element are very small. Often the workaround is to apply much higher roughness values in order to 'slow the flow'. It would be helpful to have a depth varying roughness that could be phased out as the water depth increases. This would put ICM in line with how TUFLOW and Flood Modeller Pro deal with the problem.