Stream water quantity is the most basic, fundamental and important element for stream water quality and for conservation
of ecological environment. This study aims to analyze causes of changes in stream water quantity based on the percentage
of impervious surface area (%ISA) in urban streams of Gyeonggi-do, and also to present a method to secure water
quantity of urban streams in Gyeonggi-do and data to be applied to River Management Policy. For this purpose, the
Anyangcheon watershed, the Tancheon watershed, and the Osancheon watershed were selected as samples of the urban
streams. In addition, the stream water quantity and the changes in stream water quality which were based on the amount
of ISA, and methods to directly and indirectly secure stream water quantity were investigated. The results are as follows.
The amounts of ISA of the Anyangcheon watershed, of the Tancheon watershed, and of the Osancheon watershed showed
a 5.32%, 6.32%, and 7.22% increase, respectively, from 2014 which was approximately 10 years ago. The runoff
coefficient generally increased as the amount of ISA was increased. Water reuse quantity of stream in the Tanchon
watershed had a positive effect on securing stream water quantity, but both in the Anyangcheon watershed and in the
Osancheon watershed, it did not have a positive effect on that. However, water reuse quantity of stream improved the
water quality of each stream.