Urbanization of watershed exerts bad influence on circulation of water, shapes of rivers, or water quality, etc. for which urban rivers suffer from flood, dry stream phenomenon, or deterioration of water quality. Especially, watersheds adjacent to the cities receiving constant development pressure are badly affected by disordered development. Nevertheless, policies to cope with these problems are rather insufficient. Although approaches are emerging recently in Korea to deal with these problems in the aspect of watershed management, practical methodological studies still run short. So it is deemed desirable to clarify the factors affecting the water circulations or conditions of rivers in the cities, and utilize them as management indexes in the course of watershed management.
Watershed management indexes include impervious surface, population density, and urban land utilization, etc., among which impervious surface index is the most adequate to be used as a method of watershed management. Impervious surface index could be the most useful index for watershed management not only because it is efficient in managing watershed, but also because management is possible through the introduction of various watershed management techniques such as reduction of impervious surface or increase of permeability ratio.
Impervious surface consists of two major factors, the rooftops under which we live, work, and shop, and the transportation system connecting the rooftops. In most cases impervious area related to the transportation system exceeds those related to the rooftops(house, bu