ALSO called Hydraulic radius is defined as:\(R = \frac{{WETTED\;Area}}{{Wetted\;PERIMETER}}\)Calculation Wetted area, \(A = \frac{\pi }{4}{D^2} = \frac{\pi }{4}{m^2}\)Wetted perimeter, P = πDP = π × 1 = π mHydraulic radius, \(R = \frac{A}{P}\)= \(\frac{{\frac{\pi }{4}}}{\pi } = \frac{1}{4}\)R = 0.25 mNote:Other important relations:1. Hydraulic Depth (D)\(D = \frac{{Wetted\;Area}}{{Top\;Width}}\)2. The rate of change of wetted area with RESPECT to depth of flow is equal to top width i.e.\(\frac{{\;dA}}{{dy}} = T\)