The provision and disposal of water for urban populations is as old as the development of cities themselves. Unrestrained development has made the task ever more difficult and hydrologists and civil engineers face constant pressures to stay on top of the challenges of providing sufficient supplies and adequate treatment/disposal of effluents.
Urban areas have long existed as centres of trade, culture and government, with large-scale population migration away from rural areas to towns and cities increasing rapidly in the last century. Pressures on housing and services have brought specific problems to be solved, including high-rise buildings, mass-transport systems, dormitory and satellite towns, and out-of-town commercial parks. The impacts of such urbanization on catchment hydrology vary according to the local environment, development history and economic constraints on meeting water needs. These needs include water supply for domestic and industrial use, a waste water disposal system, a drainage system to control groundwater and remove local flood water, plus a flood defence system to protect against inundation from external areas. The effects of such developments need to be assessed to see how they interact with the ‘natural’ processes of rainfall, groundwater and drainage that are themselves modified by urbanization.