Neco 2022 Geography Question 29

A catchment of total area \(12\ \text{km}^{2}\) is divided into two sub‑areas. Sub‑area A1 occupies \(30\%\) of the catchment and has a runoff coefficient \(C_{1}=0.35\); sub‑area A2 occupies the remaining area with coefficient \(C_{2}=0.55\). A design storm lasts 30 minutes. During the first 15 minutes the rainfall intensity is \(90\ \text{mm\,h}^{-1}\) and during the next 15 minutes it falls to \(70\ \text{mm\,h}^{-1}\). Using the rational method \[ Q = 0.278\, C\, i\, A, \] where \(i\) is the intensity (mm\,h\(^{-1}\)), \(A\) the total area (km\(^2\)) and \(Q\) the peak discharge (m\(^3\) s\(^{-1}\)), determine the peak discharge considering the higher intensity period only. Give your answer to one decimal place.