Gce Model Questions Vol1 2018 Geography Question 17

A drainage catchment consists of two sub‑catchments. Sub‑catchment A has an area of 5 km², runoff coefficient 0.4 and a main channel length of 2 km on a 5 % slope. Sub‑catchment B has an area of 3 km², runoff coefficient 0.6 and a main channel length of 1.5 km on an 8 % slope. The design storm intensity is obtained from the IDF relation \(I = \frac{200}{(t_c+5)^{0.6}}\) (mm h⁻¹), where \(t_c\) is the time of concentration in minutes calculated by Kirpich's formula \(t_c = 0.0195\,L^{0.77}S^{-0.385}\). Using these data, compute the peak discharge from each sub‑catchment (in m³ s⁻¹) and the total peak discharge. A proposed culvert has two capacity options: 30 m³ s⁻¹ (Option 1) and 35 m³ s⁻¹ (Option 2). Which option satisfies the design requirement?