하천댐의 어도현황과 향후 설치 및 관리방안 연구

Abstract

These days, it is apparent that people increasingly consider rivers as, not only as subjects of irrigation and flood control, but as an environment which should be well maintained along with the human beings. One such example is development of technologies for recovering river functions. These technologies focus on rivers' ecological functions including the recovery of the functions, in regard to the consolidation and management of rivers. A part of such movement is the significant stress placed on minimizing the environmental impact during various river and dam projects and on recovery of the already damaged ecosystems. One of the representative projects is installation of the fish ways. In case of Korea, all 216 fish ways - mainly fish ladder or baffled channel types that are mostly located in Gangwon-do (province) - were installed around the country up until 2000. However, no fish ways are installed in some provinces such as Chungcheongbuk-do, and even for those which have been already constructed, only a few are well-installed. Ever since 2000, more fish ways have been installed as the installation of the fish ways became mandatory at reservoirs in accordance with the revisions made in the Fisheries Resources Protection Decree. The fish ways have never been evaluated after their construction, since there are no experts, design standards, or experiences on fish way installation at this point. Also, fish way installers often modified cases from abroad without understanding the actual principle. Against this backdrop, the objective of this study is to identify the relevant problems and suggest improvement schemes for installation and management of the fish ways. The Chapter 2 deals with general issues for understanding of fish ways: the history on how the concept of fish ways have developed so far; recent studies; purposes for installation; relevant laws and regulations in Korea; design conditions and considerations; and types of fish ways. We have stressed, in particular, the fish way types in regard to the classification, description, selection, and comparison of advantages and disadvantages. The Chapter 3 is focused on the status of fish ways at dams for all four major rivers in Korea (i.e. Hangang, Nakdonggang, Geumgang, and Seomjingang). First, the water systems are classified, key facilities including dams for each system are identified, and each of them are investigated based on existence and type of the fish way(s). The Chapter 4 introduces the data mainly focusing on countries like USA and Japan. For USA, the investigation focused on the two river systems adjacent to the northwest coast and the east coast respectively. The last chapter summarizes the problems with the existing fish ways and introduces some of the general measures to solve them for formulating schemes for improving fish ways in Korea. Then, different schemes are reviewed for efficient installation and management of the fish ways. Types of fish ways most widely constructed in Korea are fish ladders, ice-harbors, modified vertical slots, and baffled channels. Analyzing their current status proved that the fish ways are used not only by profitable fishes (e.g. salmon, sweetfish), but also by all other living organism in the river, such as Chinese mitten crabs, oriental river shrimps, melanian snails, and dragonfly larvae. It was found that the users move through the fish ways from the early March, when the water temperature rises to approx. 10℃, to late November, when it falls below 10℃. The investigation, furthermore, revealed that the fish ways are often used when fry spread away from their mothers and when fish come back upstream after being swept away by floods, as well as when they move upstream for spawning. Ice-harbor fish ways with slope below 1/20, in particular, were used, regardless of their power in jumping and swimming, by all fishes living in the rivers, including very small ones such as common minnows 17 mm and Coreoperca kawamebari (scientific name) 20 mm in length. Full-face fish ways made of stones, however, were found difficult for fish to use due to their lack of water flow. Also the current status of fish ways in other countries were surveyed. In Japan, they have installed fish-ladders, vertical-slots, ice-harbors, full-faces, and artificial-channel fish ways, mainly for profitable fishes such as sweetfish, trouts, and eels. Recently, however, they are constructing fish ways for preservation of ecological environment. In USA, they have also installed fish-ladders, vertical-slots, ice-harbors, and artificial channel fish ways, mainly for salmons. They are now also constructing fish ways for preservation of ecological environment. Those installed in Canada (45% of the Denil type) are mostly for salmons and large migratory fish. In case of Europe, although the fish ways were often not fully functional due to wrong design and location, after establishing the fish way design principles, they have constructed fish ways mostly of the natural channel type. In regard to the fish ways installed in Korea, there are problems in managing the downstream scour, drifting logs (or wastes), fishing, and keeping them closed. Such problems often block the fish ways with deposits and wastes, and thus disturb the fish passing through or moving upstream. For technological problems, on the other hand, the locations are not well selected. Fish ways, for example, are sometimes installed at the center, although they should be installed at the left and/or right of the reservoirs. Even if a fish way type should be selected according to the characteristics of the river or reservoir, the existing one is often maintained without any change. Fish ways are frequently constructed, without any expert's advice, on the basis of the engineer's imagination. The slope is often ruled below 1/10, furthermore, although it should be below 1/20 at most. It is necessary for improvement of such problems, to establish and implement management methods and frequencies. Also, fishing village cooperatives, local authorities, and civil organizations should be designated as main bodies in managing fish ways and restricting fishing, and to perform regular training for designers, constructors, and managers in order to enhance the efficiency and continuity of management. It is also necessary to prevent installation of unclear or uncertain fish ways by preparing standard drawings by fish types and distributing them to every local authority and national organization. Relevant design and construction, in addition, should be properly conducted to the appropriate roles, through revision of fish way design standards and instructions included in the river and dam design standards. After installation, furthermore, fish ways should be verified by continued monitoring, and thereby calibrated and corrected. Such efforts will significantly facilitate the development of fish ways which conforms to local characteristics of each area.