ABSTRACT

The circulation of water in the city involves two interlinked systems: the people-modified hydrological cycle and the people-created artificial supply and waste-water disposal system. The natural circulation of water is modified by the nature of the urban surface, with large impermeable areas that encourage rapid runoff and decrease infiltration. The urban heat island and energy balance affect rain-producing mechanisms and the rate of snow-melt over and within cities. Urbanization affects stream channels and flood plains, often causing water to flow through cities at higher velocities. These hydrological effects of urbanization may be summarized under four major headings (Leopold 1968):

1 a change in total runoff 2 an alteration of peak flow characteristics 3 a decline in the quality of water 4 changes in the hydrological amenities of stream and their ecology.