A $1$ m wide rectangular channel has a bed slope of $0.0016$ and the Manning’s roughness coefficient is $0.04$ Uniform flow takes the place in the channel at a flow depth of $0.5$m. At a particular section, gradually varied flow (GVF) is observed and the flow depth is measured as $0.6$ m. The GVF profile at section is classified as

1. $S_1$
2. $S_2$
3. $M_1$
4. $M_2$