A rectangular channel with Gradually Varied Flow $\text{(GVF)}$ has a changing bed slope. If the change is from a steeper slope to a steep slope, the resulting $\text{GVF}$ profile is
- $S_{3}$
- $S_{1}$
- $S_{2}$
- either $S_{1}$ or $S_{2}$, depending on the magnitude of the slopes