If using material values (M), the Manning’s n value to be applied is taken from the .tmf file (see Read Materials File). If the “P” flag is not used, the material at the lowest Z value (cross-section bed) is used as the primary material, which then corresponds to a relative resistance factor of 1.0. If no material values are specified, a material value of one (1) is applied over the whole cross-section. If the P flag and values are used, the primary material is determined as that at the lowest Z value in the mainstream channel (see Section 3.13.5.3).
When using materials, the Mannings_n value in the 1d_nwk layer becomes a multiplier and should be set to one (1.0).If justified, it can be adjusted for calibration purposes. For example, if a slightly higher resistance is desired along a channel, rather than setting different material values, change the Mannings_n value in the 1d_nwk layer to, say, 1.1 to increase all Manning’s n values across the cross-section by 10%.
A material value of –1 ignores that section of the profile.
