Definition of the roughness (Manning)

In English and Spanish interfaces, the roughness coefficients are input in terms of Manning. In interfaces in French the roughness coefficients are input in terms of Strickler which is the inverse of Manning:  n=\frac{1}{K_{S}}

To access the input interface of the roughness coefficients:

  • Tools menu> Setting Manning
  • Button

The sections are selected directly on the graph or the tree view. It is also possible to refine the selection and capture coefficients between two abscissas even though there is no data sections to these abscissae [1]. The abscissa and the coefficients are entered in the right side of the screen:

  • Manning min for the minor bed
  • Manning med for the medium bed if exists

The coefficient is represented on the graph by a color scale:

  • The radio buttons let you choose the Manning plotted (minor or medium bed)
  • In the ’view’ toolbar , the button allow to display or not the legend of the coloring
  • In the menu "Display> Change the color chart," you can also change the settings of the coloration

Usual values ​​of the Strickler coefficients n [2]

Type of stream Usual values ​​of n (s/m1/3)
Concrete channel, very smooth 0.010 - 0.013
Concrete channel, average state 0.013 - 0.020
Earthen canal 0.020 - 0.033
Regular stream, well maintained 0.020 - 0.025
Ordinary stream 0.025 - 0.033
Stream with jams 0.033 - 0.050

[1The coefficients will be applied to the closest calculated sections

[2Extract from "Hydraulique pour le génie rural", J.-P. Baume, G. Belaud, P.-Y. Vion (Avril 2006)