In the case of a singular section it is necessary to have two computational sections at the same abscissa. If the model user entered two data sections at the same abscissa, both these sections are retained as computational sections. If only one section was entered, the downstream computational section is interpolated using the singular data section and the data section immediately downstream with a 1 m step. The interpolated section is then placed at the same abscissa as the singular section (see figure 14).

Figure 14

Section k is interpolated between sections i and j with a 1m step and is then placed at the section i abscissa. Therefore, one has to take care to enter two sections (i and j) at the same abscissa, especially if the bed elevation upstream and downstream of the device is different or if the section dimensions are different.

Figure 15

In figure 15, one will enter the two cross sections (i and j), as shown, but j will be given the same abscissa as i, so that there will not be any interpolation.