Neco 2020 Geography Question 44

A rectangular catchment measures \(2\) km by \(1.5\) km and has an average slope of \(5\%\). The land use gives a runoff coefficient of \(0.6\). A design storm of intensity \(20\) mm/hr lasts for \(2\) hours.\n(a) Using the rational method, calculate the peak runoff discharge in cubic metres per second (m³/s).\n(b) The proposed drainage pipe can convey \(15\) m³/s. Is it adequate?\n(c) Estimate the time of concentration using the Kirpich formula \(T_c = 0.0195 L^{0.77} S^{-0.385}\) (where \(L\) is the longest flow path in metres and \(S\) is the slope expressed as a decimal) and comment on whether the storm duration is sufficient for the peak discharge to be reached.