If the distance between two data sections is more than one computational (space) step, the program interpolates computational sections between these two data sections, in accordance with the step decided by the user.

In reality, the space step is adjusted in order to give a whole number of equal computational intervals between the two sections considered. The interpolation is performed at constant water depth.

In the figure below, the interpolated widths in each data section that enable to obtain all the widths of the computational section are shown in broken lines.

A computational section could thus have up to double the number of points of the data sections. One must therefore adopt some criteria to eliminate some points and to avoid storing too many points.

Any point of the computational section which does not modify the section area by more than 1 % is eliminated. Similarly, all points which do not modify the wetted perimeter by more than 5 % are excluded. Therefore, whatever the water depth may be, we can expect a precision of 1 % regarding the estimation of the area and 5 % regarding the wetted perimeter.

The computational sections are completed vertically by a fictitious point located 500 m above the canal bank elevation in order to allow calculation even if overtopping occurs.

The computational sections are numbered within each reach, so that if the computational space step is modified in any given reach, the numbering of the sections within other reaches will remain unchanged.