Neco Model Questions Vol1 2023 Geography Question 36

A small catchment has a total area of 12 ha. The land use is 40 % forest (runoff coefficient 0.30) and 60 % cultivated (runoff coefficient 0.60). The catchment length along the main stream is 800 m and the average slope is 5 %. Using the Kirpich formula \(T_c = 0.0195 L^{0.77} S^{-0.385}\) (with \(L\) in metres and \(S\) as a decimal), calculate the time of concentration \(T_c\) (in minutes). The rainfall‑intensity‑duration data are: 10 min → 100 mm h\(^{-1}\), 30 min → 70 mm h\(^{-1}\). Assuming intensity varies linearly with the logarithm of duration, estimate the intensity for the computed \(T_c\). Finally, using the rational method \(Q = C i A / 360\) (where \(i\) is in mm h\(^{-1}\) and \(A\) in ha), determine the design peak discharge \(Q\) in m\(^3\) s\(^{-1}\).