Indicative 2D roughness values
Table of 2D roughness values
Flood risk modellers can use the following 2D roughness vales as a starting point to assess, review and update their data when developing a hydraulic flood risk model.
Descriptive group |
Feature codes from OS MasterMap (Multi-coloured Manual) |
n value |
---|---|---|
Roads, tracks and paths | 10119 (Manmade) 10172 (Tarmac) 10183 (Pavement) |
0.02 |
General surfaces | 10054 (Step) | 0.025 |
Roads, tracks and paths | 10123 (Tarmac or dirt tracks) | 0.025 |
General surfaces | 10056 (Grass, parkland) | 0.03 |
Structures | 10185 (Roadside structure) | 0.03 |
Water |
10089 (Inland) 10210 (Tidal water) |
0.035 |
Land (unclassified) | 10217 (Industrial yards, car parks) | 0.035 |
(Default value) | (9999) | 0.035 |
General surface | 10053 (Residential yards) 10093 (Unspecified) |
0.04 |
Heritage and antiquities, land | 10096 (Landform, historic interest, slope) | 0.04 |
Water, land | 10099 (Cliff) 10203 (Foreshore) |
0.04 |
Structures | 10193 (Pylon) | 0.04 |
Rail | 10167 (Unspecified) | 0.05 |
Natural Environment (Coniferous / Non-coniferous Trees) | 10111 (Heavy woodland and forest) | 0.1 |
Land; Heritage and Antiquities | 10076 (Unspecified) | 0.5 |
Building | 10021 (Unspecified) 10062 (Glasshouse) |
0.5 (to be confirmed. Lower values to be considered for 'porous buildings') |
Structures | 10187 (Generally on top of buildings) |
0.5 (to be confirmed. Lower values to be considered for 'porous buildings') |
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