유역관리 효율화를 위한 불투수면 지표 개발과 적용(II)

Abstract

Even though the changes in the use of watershed land are an important factor which affects the quality of water, they have been rarely taken into account in management of water quality. As the land uses and economic activities in the watershed are increasing, we can no longer prevent the deterioration of water environment only with the old means of environmental management such as sewage treatment. Also, the need for developing and using new watershed management indicators that enable us to better manage land use is growing. Among these new indicators, Impervious Cover is being considered as a factor that closely affects water quality in a negative way, and its importance in water quality management is being highlighted. This study reviewed the effects of increased Impervious Cover on the water quality and volume in watersheds. In addition, the practices of using Impervious Cover Indicators for watershed management, and methods for reducing impervious covers are examined. As a plan to reduce impervious covers to cut down their negative effects on watershed environment, considerations that must be taken at the land use planning stage, and after the development of land were introduced. Particularly, various methods of land use and its management to reduce impervious covers were examined, and environmental and economic benefits that can be obtained by applying these methods in actual watershed planning activities were also presented. To summarize the contents of each chapter, Chapter 2 describes a positive analysis of the influence of the impervious covers and reviews various effects from the increasing impervious covers. The analysis of the influence of impervious covers was carried out for Gyeongan stream, Anyang stream, and Bokha stream watersheds. Chapter 3 describes the methods adopted in some countries to manage impervious covers and reduce their influence on water environment. These countries are trying various methods to relieve their negative effects on water quality, water volume, and ecosystem. These effects include difficulties of water circulation resulting from the increasing impervious covers due to growing economic activities, buildings and pavements in watersheds. Chapter 4 describes various measures to apply the impervious cover reduction methods. These measures for facilitating water circulation and cutting down pollutant runoff in watershed can be largely classified into two groups: the measures that take into consideration the causes and influence of impervious covers in the land use planning stage in advance and the measures to reduce rainwater runoff and pollutions by using physical facilities after the land is developed. Advance measures include limiting the percentage of imperviousness in the land use plan or considering water circulation in site planning. The posterior measures include the installation of pervious areas and undercurrent facilities to reduce impervious covers. The last chapter, "Conclusions and Policy Suggestions" presents the methods to cope with problems caused by the increased impervious covers in watersheds such as the growing runoff ratio, the reduced time of flood concentration, infiltration (internal water exclusion), increased peak runoff, reduced underground water infiltration, and increased nonpoint pollutant runoff. In summary, three basic suggestions are made. The first suggestion is that we should take into account a rainwater circulation system at the land use planning stage; in particular, some measures to minimize hydrological influence generated by site development through site design, and to relieve or restore the inevitable disturbance to the hydrologic system. The second suggestion is that we need institutional support; in other words, we should improve the specifications and regulations related to urban development that increases impervious covers. In particular, we should revise the regulations on the collection and exclusion of rainwater falling on the ground so that the rainwater would not directly flow into rainwater baskets but pass through surrounding pervious areas such as greens. In this way, we can expect to reduce runoff as well as cultivate underground water through rainwater infiltration. Furthermore, we should consider expanding pervious pavements that are used in some areas, such as bicycle paths, parking lots, and roads in housing areas that have a low traffic load. The third suggestion is that we should expand anti-inundation projects in cities. As measures for decreasing the total volume of inundation, we should actively consider such measures as the preservation of rainwater infiltration and natural areas, use of roof rainwater, as well as anti-inundation measures using rainwater undercurrent such as the installation of underground streams and underground water reservoirs. These measures for facilitating the rainwater infiltration, runoff control and reuse will not only normalize the water circulation system in watersheds but reduce the runoff of nonpoint pollutants as well as giving positive effects to the overall water environment including the water quality, water volume, and ecosystem of watersheds.