The formula to calculate the flow velocity is:

\[ V = C \cdot \sqrt{R \cdot S} \]

Where:

• \(V\) is the flow velocity in meters per second (m/s).
• \(C\) is the coefficient of roughness, ranging from 50 to 180.
• \(R\) is the hydraulic radius in meters (m).
• \(S\) is the slope of the water surface, expressed as a decimal.