Chezy's and Manning's coefficient for Seti River

Given data

Bed slope $S=\dfrac{10\ \text{cm}}{1\ \text{km}}=\dfrac{0.1}{1000}=1\times10^{-4}$, hydraulic mean depth $R=2.5$ m, $V=2.4$ m/s.

Chezy's coefficient

$$V=C\sqrt{RS}\;\Rightarrow\;C=\frac{V}{\sqrt{RS}}=\frac{2.4}{\sqrt{2.5\times10^{-4}}}=\frac{2.4}{0.015811}=151.79\ \text{m}^{1/2}/\text{s}$$

Manning's coefficient

$$C=\frac{R^{1/6}}{n}\;\Rightarrow\;n=\frac{R^{1/6}}{C}=\frac{2.5^{1/6}}{151.79}=\frac{1.1650}{151.79}=0.00768$$

(Check with Manning: $V=\dfrac1nR^{2/3}S^{1/2}=\dfrac{1}{0.00768}\times1.842\times0.01=2.40$ m/s.)

Answer: $C=151.8$ m$^{1/2}$/s and $n=0.0077$ s/m$^{1/3}$. The value of $n$ is very low for a natural river; it follows directly from the data as given.