A very wide rectangular channel carries a discharge $Q=70~\mathrm{m^3/s}$ per meter width. Its bed slope changes from $S_0=0.0001$ to $S_0=0.0009$ at a point $P$ (not to scale). The Manning's roughness coefficient is $n=0.01$. What water-surface profile(s) exist(s) near the point $P$?