I have problems calculating the roughness values and have not been able to find this subject on the manual, would appreciate any help
The roughness values for FaSTMECH can be entered as drag coefficients or z0 (roughness length). The drag coefficient varies in natural rivers between about 0.001 (very smooth) to .1 (very rough), with most rivers falling in the range between 0.005 and 0.05. We generally recommend having water-surface elevations for calibrating this value over a reach or in particular areas. Note that the drag coefficient is nondimensional. You can also relate this to the Mannings n value if you have a depth estimate.
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