Another way to describe a cross section is to enter, for each value of elevation, the section width as drawn in figure 5. That is, one should input couples (Zi, Li), starting from point 1 (decreasing width-elevation), or from point 4 (increasing width-elevation). This description is generally adopted when one does not have precise information on the section or if the section is symmetrical.

Figure 5

If one enters the cross-section in width-elevation couples, any asymmetry in the section is not taken into account. The wetted perimeter is computed assuming a symmetrical section. The only way to take into account an asymmetrical section is to enter it in terms of abscissa-elevation couples. A closed section can also be represented this way, but in this case, width L1 of the figure would be equal to zero.