Neco Model Questions Vol1 2020 Geography Question 39

A river flows from point X at an elevation of 250 m to point Y 30 km downstream at an elevation of 150 m. The channel has a rectangular cross‑section 10 m wide and an average depth of 2 m. The side slopes of the valley are 1 vertical : 2 horizontal.\n\n(a) Calculate the average longitudinal slope \(S\) of the river (dimensionless).\n(b) Using the simplified shear stress formula \(\tau = \rho g R S\), where \(\rho = 1000\) kg m\(^{-3}\), \(g = 9.81\) m s\(^{-2}\) and the hydraulic radius \(R\) may be approximated by the flow depth (2 m), compute the bed shear stress (in N m\(^{-2}\)).\n(c) The critical shear stress for the dominant bed material is \(0.30\) N m\(^{-2}\). State whether the river is capable of eroding its bed under the given conditions.