기후변화 대응을 위한 적정 하천공간 확보방안 연구 I

Abstract

Sustainable Spatial River Planning for Climate Change There have been difficulties to use and control water resource in Korea because of its regional and seasonal deviation of precipitation. To overcome these difficulties, river restoration plans, such as 4 major rivers restoration project have been conducted. In spite of these efforts, the damage of drought and flood is continuously increased; besides, most of river spaces have been converted to farm or urban land by the result of industrialization and urbanization. This phenomenon has changed river space into low level land for farming and habit, aggravated flood damage and caused more economic loss. Current passive river restoration project focuse on levee improvement as a countermeasure for climate changes has lots of limitations. Therefore, comprehensive river space plans that increase water storage capacity by securing vertical and horizontal river spaces need to be prepared for reduction of natural disaster and for coexistence of the nature and human. This study provides a new comprehensive approach as countermeasures of climate change for water control(reduction of flood damage), water use(security of water resource), water quality, ecosystem and culture, through the function of original river space, beyond the river boundary from current water-course act. For this purpose, this study shows the flood analysis for climate change, case study for river space restoration, river space restoration plan, integrated plan of river space. The conclusion is as follow. First, the flood for 500yr frequency on climate change was simulated for the estimation of possibly occurable flood level and hazard on Nakdong-river, designed by 100yr or 200yr frequency. And also the economic feasibilities of levee improvement and river space extension with resident emigration were estimated. With those results, the necessity of sustainable flood countermeasures was emphasized. From the result of simple comparison between flood level of 200yr frequency and levee level, about 90% of all spots were safety. However, when freeboard of levee was considered, the percentage of safety spot was down to about 40%. In case of flood level of 500yr frequency, when the freeboard was not considered, the percentage of safety spot was about 40%. When the freeboard was considered, the percentage of safety spot was down to 29%. When dredge is executed, the safety ratio increases for 200yr and 500yr frequency. However, flood hazard is not totally eliminated. Therefore, for the improvement of river environment and the reduction of flood hazard, a multi-dimensional river improvement project such as the security of river space is more necessary than one-dimensional project such as dredge. With the assumption that water control project must be executed for the prevention of flood damage, current levee improvement projects and inhabitant movement through the land purchases were compared on the downstream of Nakdong-river(junction of hwang-river and Nam-river) using multi-dimensional flood damage analysis(MD-FDA). From the results, benefit of inhabitant movement plan was same with that of levee improvement plan. However, the total sum of reduction cost and benefit-cost ratio on inhabitant movement plan was relatively higher than that of levee improvement plan. At this point in time, the water control project based on the structural approach viewpoint has been lead to limitation. To overcome natural disaster according to climate change, the security of river space is necessary for the reduction of flood through natural restoration and storage space. Second, in countries such as Europe, USA, and Japan, alternative approach has been conducted not to reinforce levee but to secure river space for dynamic river characteristics and to conserve life, nature, culture and historical sites. In the Netherlands, ‘Spatial Planning Key Decision Room for the River(SPKD)‘ was established for prevention of flood damage and improvement of environmental quality in a watershed. They have secured river space according to the change of paradigm from levee reinforcement to river space security. In other countries such as Germany, Swiss, and Austria, river and flood plain were restored as a natural formation through the security of former river space in the respect of environmental conservation and water control. These countries have developed various river management plans including the improvement of levee, the construction of storage space, and the control of development through the purchase of flood plain. In USA, the integrated plan of upstream of Mississippi-river has considered the economic, environmental, social respects. In Japan, a river is managed as a space that nature and human can coexist with considering water control, water use and environment, beyond the existing policy on water control and use. River space located in a regular distance from river is developed as eco-ponding flood storage through the security of river space. And, in case of urban area where the price of land is high, they lower the flood hazard through the construction of super levee, underground storage space, underground tunnel, permeable pavement, and so on. In the case of Korea,, the studies on the security and the restoration of river space have been accomplished since 2006. However, from the political respects, the researches on flood and drought according to climate change, difficulties on the security of water quantity for sustainable eco-river, the deterioration of water quality caused by the incensement of pollutant sediment, are insufficient. Therefore, it is necessary to develop the spatial river plan and policy on the security of river space considering water control, water use, ecosystem, culture, rural development. Third, since 1970's, river space had been occupied by farmland or parking place and the relationship between nature and human has been disconnected by roads. Stream flow depletion was caused by the diversification of land use such as the reduction of agricultural drainage system by the urbanization of farmland, the reduction of channel by the conversion of farmland nearby urban area. To prevent damages from natural disaster in such river space, levee had been constructed in river space; however, this construction accelerated stream flow depletion. It caused the reduction of inhabitation spaces such as bio-top, wet land, the grove of animals and plants. The problem of current river management plan resulted from the present linear construction method of river and low understanding about surround environment. The security of integrated river space that connects river space and cultural resources together has been suggested as an alternative approach for the dynamic characteristics of rivers that conserve not only water control, water use, nature but also life, culture, historical assets. In this research, Milyang (Nakdong-river) and Naju(Youngsan-river) areas were selected for integrated spatial plan and various features and factors that are closely related to those sites have been studied and examined. Forth, disasters relief policy such as the regulation of land use, the development of flood forecasting system, flood map, flood insurance program. were presented because integrated management could not be executed only with river spatial plan. The importance of cooperative governance system with NGO, residents, corporations, public service personnel, experts were emphasized because river space could not be extended without resident's interests and the river management project need lots of budget and highly technical project. This research has an implication in that it provides new river strategies for climate change with the approach of surface-dimensional concept, unlike the former civil engineering methods. In addition, this research suggests the integrated approaches for flood control, irrigation, ecology, culture, and local economy, in other words, comprehensive flood management plans through securing of vertical and horizontal river spaces. However, to utilize the results of this research in practical policy making process, further persistent researches on short, medium, and long-term plans for utilizing and securing the river spaces need to be prepared. For the short-term plans, it is necessary to make an organizational system for security and the management of river spaces through watershed management system. And also it is necessary to determine basin boundary with previous literature and a field survey, and to establish the database on the various basin status as a preliminary work for the security and the management of river spaces. For the mid- and long-term plans, it will be necessary to prepare more systematical solutions and related policies to manage these river spaces. Moreover, these plans need to be continuously modified and advanced according to the unforeseen situations over time and there should be a program that evaluates the suitability of utilization and the management of river spaces.