5. (a) Whatever its form, precipitation results from the condensation of moisture contained in warm air when the air is cooled or forced to cool. Explain the principal methods for achieving cooling. [6 marks] (b) The measured streamflow data for a 2hr storm over a catchment of area 1.98km2 is shown in Table 1. Assuming a constant baseflow of 1m3/s, derive the 10mm 2hr Unit Hydrograph. Time (hr) Flow (m/s) Unit conversions 1 litre = 0.001 m 1000 litres 1m 1 ha = 10000 m = Table 2: Streamflow data (c) Use the hydrograph developed in (a) to determine the quick response runoff occurring when a storm of duration 4 hours falls on the catchment; total rainfall was 30mm during the first 2 hours and 105mm during the second half of the storm. Assume losses are 15mm/hr. [19 marks] 0 1 2 3 4 5 6 7 8 9 10 1 2 8 14 11 9 8 6 4 2 1 APPENDIX [25 MARKS]