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문제 정의
- This study is to analyze the changing phase in the habitat of organisms after the removal of small dams which used to block streams.
제안 방법
- Then, the names of the species were recorded and they were listed up. After that, the major plant community in the sections subject to research were prepared as a vegetation mapping. Also, the representative cross sections of the upper stream and the lower stream sections after the removal of the small dams of the rivers subject to research were selected, and were shown in a mimetic diagram.
- Through these traversal measurements, the changes in the deepest riverbed were analyzed with the removal of the small dams. Also, the grain sizes of riverbed materials, which were collected in the upper stream and the lower stream section of the dams before the removal of the dam, were analyzed. Then, the changes in grain sizes were analyzed by collecting riverbed materials again in the same places after their removal and analyzing them again.
- For the analysis of the changing phase in the habitat of organisms, the physical impacts such as the changes of the riverbed caused by the removal of the small dam, chemical impacts such as changes of the water quality before and after the removal, and biological impacts due to changes in the habitat were examined.
- In order to analyze chemical characteristics according to the removal of the small dams, the analysis was conducted in April and June(twice) before the removal of the small dams, and during four seasons(July, October, April, and June: four times) after the removal of the small dams on chosen dates when no changes occurred in the flux. In the fields, the measurement of water temperature, pH, EC, and the flux as well as DO fixation were done, and collected samples were promptly delivered to a testing lab and measured with a water quality process testing method and a standard method for items to measure(DO, SS, COD, T-N, T-P, T-P, F) in the testing lab.
- In order to analyze ecological characteristics, it was decided to conduct the testing on the same day when the analysis of chemical characteristics was done. Then, the analysis was performed in April before the removal of the small dams, in June, after the removal of the small dams(twice), and throughout the four seasons(July, October, April, and June: four times) after the removal of the small dams on chosen dates when no changes occurred in the flux, and additional investigations were undertaken only for insufficient parts.
- In order to analyze chemical characteristics according to the removal of the small dams, the analysis was conducted in April and June(twice) before the removal of the small dams, and during four seasons(July, October, April, and June: four times) after the removal of the small dams on chosen dates when no changes occurred in the flux. In the fields, the measurement of water temperature, pH, EC, and the flux as well as DO fixation were done, and collected samples were promptly delivered to a testing lab and measured with a water quality process testing method and a standard method for items to measure(DO, SS, COD, T-N, T-P, T-P, F) in the testing lab.
- It was anticipated that the feasibility that large benthic invertebrates will live in the upper stream and the lower stream basin in which there were small dams would be high or the fauna would be enriched before and after the removal of the small dams, and some points and peaks that may sufficiently represent the characteristics of the fauna in the target water system were randomly selected and collected a total of six times.
- In order to analyze ecological characteristics, it was decided to conduct the testing on the same day when the analysis of chemical characteristics was done. Then, the analysis was performed in April before the removal of the small dams, in June, after the removal of the small dams(twice), and throughout the four seasons(July, October, April, and June: four times) after the removal of the small dams on chosen dates when no changes occurred in the flux, and additional investigations were undertaken only for insufficient parts.
- Also, the grain sizes of riverbed materials, which were collected in the upper stream and the lower stream section of the dams before the removal of the dam, were analyzed. Then, the changes in grain sizes were analyzed by collecting riverbed materials again in the same places after their removal and analyzing them again.
- This study analyzed physical features(river bed change), chemical characteristics(water quality analysis) and ecological changes(fishes, benthic animals, vegetation) before and after small dam removal for smooth restoration of stream eco corridors.
- We selected Gongreung2 small dam in the Gongreung Stream and Gotan small dam in Hantan river where a demonstration project was conducted in early April 2006 and Jun 2007, and analyzed the data from monitoring.
대상 데이터
- The study chose Gongreung2 small dam (length: 76m, height: 1.5m) in the upper reach of the Gongreung Stream located in Goyang City and Gotan small dam(length: 190m, height: 2.8m) located in the Hantan River, Yeoncheon-gun, Gyeonggi-do as study sites.
이론/모형
- Then, they were analyzed with a water quality process testing method. Regarding the analysis method, SS used a Vacuum Filtration(Glass Fiber Filters, GF/C) method, BOD used an Azide Modification, DO Meter Method(YSI Mo.58), T-N used an Ultraviolet Spectrophotometric Screening Method(UV-1601PC, Shimadzu, Japan), and T-P used an Ascorbic Acid Method.
성능/효과
- After the removal the static waters of the upstream changed to flowing waters, and as diverse particles form the riverbed materials, dragonflies and melanian snails, which used to be there, were not discovered, whereas trichoptera, which did not used to be there prior to the small dam removal, appeared. There was some change to the species.
- The analysis of the grain size distribution based on the analysis of the riverbed materials showed that, in the upper reaches of the small dam, the grain size of the riverbed materials increased as the riverbed, which used to be a sedimentary layer, was eroded, while in the immediate lower reaches of the small dam, sediments accumulated during the removal work was all washed away during the flooding, and the riverbed was full of cobbles, medium-to-fine gravels and coarse sands. In this sector the erosion due to the flooding abruptly changed the riverbed materials, but is quickly stabilizing and returning to the original riverbed.
- The analysis of the mean concentration of BOD, SS and TN and TP showed that the concentration of SS was lower after the dam removal than before the dam removal except for in the upper-most reaches of the small dam, and that of BOD had significant lower values of both of the after the dam removal than before the dam removal.
- The result of this study to analyze the changes in organisms’ habitats before and after the removal of the two small dams show that the removals were substantially helpful for recovering of ecological functions of rivers.
후속연구
- These results indicate that the water quality got better after the small dam removal than before the dam removal. However, as the monitoring was conducted over a short period of tine after the dam removal, it is too early to come to any quantitative conclusion, and a longer-term monitoring is in order.
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