A river catchment has a 2-hour unit hydrograph with the ordinates 0, 3, 11, 35, 55, 66, 63, 40, 22, 9 and 2 m3/s. Assume that the base flow at time t = 0 hours is 50 m3/s and linearly increases to 80 m3/s at t = 24 hours. a) Compute the hydrograph resulting from two successive 2-hour periods of effective rain of 3 cm and 4 cm respectively. b) To prevent downstream flooding, the maximum flow to be released from the catchment is set at 280 m3/s. Calculate the space needed to store the excess water in this event (in m3).