(a) Discuss the relative strengths of groundwater resources for water supply provision. With reference to your home region, provide a well-reasoned hydrological justification for which of these two sources is more widely used. What do you understand by conjunctive use and why would you recommend the practice for your home region if it is not being practiced currently? (9 marks)
(b) Using sketches, describe the isohyetal method for determining the average precipitation over a catchment. Under which condition would you expect the isohyetal method to outperform the Thiessen polygon method and why? (7 marks)
(c) Areas bounded by isohyets drawn on the map of a river catchment are shown in Table Q4. Determine the catchment average rainfall using the isohyetal method.
Table Q4
Isohyets: 475-400, 400-300, 300-200, 200-100, 100-70
Area between isohyets, km2: 30, 35, 40, 37, 12 (9 marks)