How do you calculate the critical depth?

Critical depth in an open channel flow can be calculated using the formula ( y_c = \frac{Q^2}{gA^2} ), where ( y_c ) is the critical depth, ( Q ) is the flow rate, ( g ) is the acceleration due to gravity, and ( A ) is the cross-sectional area of flow. Alternatively, for a rectangular channel, it can also be derived from the equation ( y_c = \left( \frac{Q^2}{gB^2} \right)^{1/3} ), where ( B ) is the width of the channel. The critical depth represents the depth at which the specific energy is minimized for a given flow rate.