ABSTRACT
Hydrology is the science that describes the occurrence and behaviour of water above, over and through the Earth. The continuous movement of water is called the hydrological cycle, because the amount of water remains fairly constant over time. The hydrological cycle is driven by solar energy and gravitation that cause continuous interrelated processes such as evaporation and transpiration, condensation, precipitation, infiltration and runoff. In contrast to the global hydrological cycle, in urban areas there is in practice almost never a closed hydrological cycle. Many cities depend on water resources from surrounding rural areas and discharge their wastewater into the sea or rivers outside the city, so that the urban water cycle is not being closed. However, since the start of the twenty-first century, various attempts have been made to create more sustainable urban development by closing the urban water cycle in order to reduce the environmental load of cities on their surroundings and reduce the dependency of cities on water resources form surrounding areas. Textbox 5-1 gives an example of such an attempt in the case of the Aurora development in the city of Melbourne, Australia.
