• Journal of Environmental Policy
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• v.14 no.4
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• pp.45-61
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• 2015

The river environment in Korea has changed significantly after the completion of the Four Major Rivers Project due to the outdated river management methods and thus, it is necessary to modify the current river management process. A typical example of this management is dredging but it is a method that usually results in socio-environmental side effects. Therefore, in order to minimize the socio-environmental impacts of dredging, Korea is currently applying the Environmental Windows, a management practice currently being used in the United States that eliminates the risk of potentially harmful impacts of dredging. The use of statistical methods was suggested to address the issue of data insufficiency and this methodology was applied in the downstream part of the Gangjeong-Goryeong weir located within the Nakdong river basin. The results show that when performing a month of dredging, the optimal period is March whereas the optimal month to start dredging is August in case of an eight-month dredging project. If Korea's flood season is also considered for an eight-month dredging process, then October is the optimal month to start dredging. Non-structural methods such as the Environmental Windows reduce maintenance costs and also bring only short-term side effects to the environment, as opposed to structural methods such as the development of environmentally-friendly dredging machine. Given that few studies have explored this topic in Korea, the findings and suggestions could serve as basic data in studying river dredging in the future.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.71-79
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• 2011

In this study, the variation of wetting front and ground water level at the embankment constructed in the Saemangeum area were predicted considering rainfall duration times and the slope stability analysis of the embankment was carried out according to prediction results of wetting front and ground water level. The embankment was formed by dredging soils. A suction stress, a cohesion and a frictional angle of dreding soils measured by soil tests were applied to estimate the unsaturated soil properties. According to the analysis results of the wetting front and the ground water level for various rainfall duration time, the wetting front began to descend from the upper part of embankment at the beginning time of rainfall and after 1 hour of rainfall duration time. After that, the ground water level continued to ascend as the rainfall duration time was getting longer. After rainfall, the ground water level was distributed at a certain depth, and the ground water level was gradually descending as time goes by. According to the slope stability analysis of the embankment considering the variation of the wetting front and the ground water level, the safety factor of slope was rapidly reduced as the rainfall began to infiltrate into the ground, and the minimum safety factor of slope was estimated after 24 hours of rainfall duration time. Meanwhile, the safety factor of slope was increased with regaining the matric suction in the ground after rainfall.

• The Journal of Engineering Geology
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• v.29 no.1
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• pp.13-21
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• 2019

The rainfall intensity-duration curve (I-D curve) was used for selecting the dredging time of sediments behind a debris barrier which is located at the study area in Inje-gun, Kangwon Province. The I-D curve was newly suggested by using the data of rainfall-induced landslides for about 30 years from June to September in Kangwon Province. According to the monitoring results, the landslides have been not occurred during the monitoring period of the dredged sediments management system at the study area, and also all of the rainfall events were located below the I-D curve. The weight of the dredged sediments measured at the management system in the field was increased but the weight increment was small. It means that the increase of the dredged sediments was not the effect of landslide but the effect of soil erosion at the ground surface due to heavy rainfall. The weight of the dredged sediments behind a debris barrier could be known in real time using the rainfall data measured at the management system. Also, when the I-D curve is used with the management system, it is possible to select the optimum dredging time for sediments behind debris barrier.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.2
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• pp.143-156
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• 2014

We reviewed investigation status on turbidity plume in the statement of marine environmental survey(2008 to 2012) associated with marine sand extraction projects. The survey statement from seven marine sand extraction sites (extraction area of Southern EEZ, extraction area of Western EEZ, relocation zone in the Western EEZ, sea area under jurisdiction of Taean-gun, sea area under jurisdiction of Ansan City, and two discrete sea areas under jurisdiction of Ongjin-gun) in the nearshore and offshore of Korea showed that in situ observations were carried out for the dispersion and transport of suspended sediments on two areas (One is a extraction area in the EEZs, the other is an area of coastal sites). However, sampling station and range have not been selected considering physical, geographical factors (tide, wave, stratification, water depth, etc.) and weather conditions (wind direction and velocity, fetch, duration, etc). Especially turbidity plumes originating from three sources, which include suspended sediments in overflow(or overspill) discharged from spillways and reject chutes of dredging vessel, and resuspended sediments from draghead at the seabed, may be transported to a far greater distance outside the boundary of the extraction site and have undesirable impacts on the marine environment and ecosystem. We address that behaviour of environmental pollutants such as suspended solids, nutrients, and metals should be extensively monitored and diagnosed during the dispersion and transport of the plume. Finally we suggest the necessity to supplement the current system of the sea area utilization consultation and establish the combined guidelines on marine sand extraction to collect basic data, to monitor cumulative effects, and to minimize environmental damages incurred by the aftermath of sand extraction.