• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.46-46
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• 2015

강우가 지역별 계절별로 편중되어 있는 우리나라는 수자원의 안정적인 확보와 이용을 위해 다양한 형태의 댐을 건설하여 운영하고 있다. 그러나 대부분의 댐건설을 통해 형성된 저수지들은 탁수 장기화 및 녹조 발생 등의 환경, 생태적인 문제를 겪고 있으며, 그에 따른 사회적 우려로 인해 신규댐 건설을 통한 수자원확보는 더 이상 어려운 실정이다. 이러한 문제에 대응하기 위한 대안으로 기존 댐 저수지들(안동호-임하호)의 구조적 연계운영방안이 진행되고 있다. 본 연구의 목적은 2차원 CE-QUAL-W2모형을 활용하여 안동호와 임하호의 구조적 연결에 따른 탁수의 이동과 각 저수지 내에서의 유동 변화를 해석하는데 있다. 저수지 연계 시나리오는 EL. 138 m 위치에 길이 2 km, 직경 5.5 m 의 콘크리트관(마찰계수 0.05)이 안동호 좌안인 임동면 마리와 임하호 우안 망천리를 연결하는 것으로 가정하였다. 모델의 보정은 실측자료가 풍부한 2006년도 수문사상을 대상으로, 개별 저수지에 대해 수행하였고, 탁수 유동 시나리오 해석은 임하호에 심각한 탁수장기화 문제가 발생했던 2002년을 대상으로 댐 연계 탁수모의를 수행하였다. 안동호와 임하호의 댐 앞에서 모의값과 실측값을 오차를 분석한 결과 탁수예측오차는 AME 0.5~24 mg/L, RMSE 0.7~30.2mg/L의 범위로 비교적 실측값을 잘 반영한 것으로 나타났다. 임하댐의 경우 탁수층의 위치와 두께, 그리고 최고 탁도값을 적절히 재현 하였지만, 안동댐은 최고 탁도값 예측에서 다소 오차가 발생하는 것으로 나타났다. 안동호와 임하호 단독 운영시와 연계 운영시의 탁수변화 파악을 위해 초기 홍수사상이 발생한 8월 이후부터 저수지내의 TSS농도 분포를 비교하였다. 안동호의 경우 댐앞지점의 탁수분포는 수온성층구조에 영향을 받아, 단독 운영시(EL. 130 m)보다 연계운영시(EL. 140 m)에 탁수의 중심이 높은 위치에 형성되었다. 단독 운영시 10월 이후에 전도현상으로 인해 침강되지 않은 잔류 탁수층이 저수지 하부로 확산되었지만, 연계 운영시에는 재부상 되어 상층으로 확산되는 것으로 모의되었다. 또한 연계운영시 유량이동으로 인해 안동호의 탁수 댐앞 도달시간이 짧아지는 것으로 나타났다. 반면 임하호는 연계 운영시 안동댐으로 유출이 생기면서 중층에서 탁수량이 저감되는 것으로 모의되었다. 저수지 내 탁수량 분석을 위해 SS 15 mg/L 이상의 잔류 탁수량을 분석한 결과, 연계운영시 안동호의 평균 잔류탁수량 비율은 11.8% 증가, 임하호의 경우 11.7% 감소하였다. 또한, 탁수의 댐하류 방류일수도 SS 15 mg/L 기준 임하호 9일 저감, 안동호는 70일 증가하여 임하호의 탁수가 안동호의 탁수 장기화에 영향을 주는 것으로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.302-307
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• 2009

물리적인 조류제어 기술에 해당하는 수류 차단막(이후 차단막)은 유입하천의 수류를 차단 또는 우회시켜 영양염류가 저수지의 유광층으로 공급되는 것을 차단하고 본류 수역으로의 조류 확산을 방지하는 기능이 있어 일본에서는 저수지 녹조제어 대책으로 자주 활용된 바 있다. 그러나 이러한 차단막은 국내 저수지와 같이 홍수시 유입 유속이 크고 수위변동이 심한 환경에서는 설치효과가 검증되지 않아 현장적용에 앞서 수치모의를 통한 효과 검증이 선행되어야 하며, 최적 규모와 위치 선정도 필요하다. 본 연구에서는 수위변동이 심한 국내 저수지 특성을 고려하여 차단막이 수위변화에 따라 상하로 이동할 수 있도록 기존 CE-QUAL-W2(이후W2) 모델의 알고리즘을 수정하고, 대청호에서 다양한 수리 수문조건에서 차단막의 기작과 효과를 예측하기 위해 가뭄년(2001년)과 평수년(2004, 2006년)을 대상으로 각각 모델을 적용하였다. 차단막 설치 예정지점은 소옥천 하류(7 m 깊이)와 댐으로부터 각각 14.9 km, 27.4 km 상류에 위치한 회남대교 아래 지점(10 m 깊이)과 대정리(10 m 깊이)로 가정하고, 모의 시나리오는 차단막을 설치하지 않은 경우(S-1), 소옥천 하류에 단독으로 설치한 경우(S-2), 소옥천과 대정리에 설치한 경우(S-3), 모든 지점에 설치한 경우(S-4)를 비교하였다. 차단막 설치에 따른 수문년 및 계절별 수질개선 효과(S-1에 대한 S-4 농도 저감 비)를 비교한 결과, 대청호에서 녹조문제가 가장 심각했던 2001년 6월$^{\sim}$8월 기간 동안 차단막은 봄-여름에 걸쳐 모든 비교 지점(회남, 댐, 추동, 문의수역)에서 Chl-a 농도를 최저(문의수역) 30%에서 최고(회남수역) 70% 정도 저감하는 효과를나타냈다. 평수년인 2004년과 2006년에는 강우사상에 따라 차단막 설치에 따른 Chl-a의 농도 저감 효과가 지점별로 다르게 나타났으며, 큰 강우사상이 6월, 7월, 8월에 걸쳐 골고루 발생한 2004년에 비해 7월 한 달 동안 집중된 2006년에 설치효과가 크게 나타났다. 수역별로 차단막의 설치효과를 비교해 보면, 유입수의 영향을 직접 받는 회남수역과 추동수역이 댐 앞과 문의수역에 비해 차단막 설치에 따른 Chl-a 농도의 저감 효과가 큰 것으로 나타났다. 그러나, 큰 홍수가 유입할 때 차단막 상류부에 집적된 조류의 일부가 수류의 포획(Entrainment) 기작에 의해 저수지 내부로 유입되는 것으로 확인되어 차단막 효과를 극대화하기 위해서는 홍수 전 차단막 상류부에 집적된 조류의 처리대책이 필요할 것으로 판단된다.

• Journal of Environmental Impact Assessment
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• v.28 no.6
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• pp.507-524
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• 2019

The purpose of this study was to validate the EFDC model for the weir pool of Gangjeong-Goryong Weir located in Nakdong River, and evaluate the effect of flow control and phosphate loading reduction on the water quality and algae biomass by group (Diatom, Green, Cyanobacteria). As a result of model validation using 2018 experimental data,the time series of water level and vertical distribution of water temperature, DO, organic matter, nitrogen, and phosphorus time series were properly simulated. Seasonal fluctuations of algae biomass by group were adequately reproduced, but the deviations between measured and simulated values were significant in some periods. As a result of scenario simulations to control the water level and flow rate, the thermal stratification was resolved as the water level was lowered and the flow rate increased. The flow velocity at which the water temperature stratification was resolved was about 0.1 m/s, which is consistent with the previous study results of Baekje Weir in Geum River. Simulations of the 2Q flow scenario showed that Chl-a decreased by 8.7% and the cell density of diatom and green algae declined. The cell density of cyanobacteria increased, however, because the high concentrations of cyanobacteria in the upstream boundary conditions directly affected downstream due to increased flow velocity. In the scenario simulation of reducing the influent phosphate load concentration (average 0.056 mg/L) to 50%, Chl-a decreased by 13.6%.The results suggest that the upstream algae concentration and phosphorus load reduction should be considered simultaneously with hydraulic control to prevent algal overgrowth of Gangjeong-Goryong Weir.

• Korean Journal of Remote Sensing
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• v.36 no.6_2
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• pp.1579-1590
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• 2020

In this paper, spatially-adaptive denormalization (SPADE) based U-Net is proposed to detect changes by using high-resolution satellite images. The proposed network is to preserve spatial information using SPADE. Change detection methods using high-resolution satellite images can be used to resolve various urban problems such as city planning and forecasting. For using pixel-based change detection, which is a conventional method such as Iteratively Reweighted-Multivariate Alteration Detection (IR-MAD), unchanged areas will be detected as changing areas because changes in pixels are sensitive to the state of the environment such as seasonal changes between images. Therefore, in this paper, to precisely detect the changes of the objects that consist of the city in time-series satellite images, the semantic spatial objects that consist of the city are defined, extracted through deep learning based image segmentation, and then analyzed the changes between areas to carry out change detection. The semantic objects for analyzing changes were defined as six classes: building, road, farmland, vinyl house, forest area, and waterside area. Each network model learned with KOMPSAT-3A satellite images performs a change detection for the time-series KOMPSAT-3 satellite images. For objective assessments for change detection, we use F1-score, kappa. We found that the proposed method gives a better performance compared to U-Net and UNet++ by achieving an average F1-score of 0.77, kappa of 77.29.

• Tunnel and Underground Space
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• v.33 no.5
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• pp.388-398
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• 2023

The changes in groundwater flow due to mining development act as a contributing factor to major issues such as ground subsidence, strength reduction and collapse. For the sustainable mining development, measures for dealing with fluctuations in seasonal underground water inflow, power losses, pump damage, and unexpected increases in inflow must be put in place. In this study, the aim is to identify the causes of underground seepage through the examination of hydrological connectivity between the study area and nearby limestone mine. A tracer tes for assessing subsurface connectivity has been planned. A variety of tracers, such as dyes and ions, were applied in lab test to select the optimal tracer material, and a hydrological model of the study area was implemented through field test. Finally, the hydrological connectivity between the external stream and underground water in the mine was analyzed.

• Ecology and Resilient Infrastructure
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• v.9 no.3
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• pp.163-173
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• 2022

Climate change is a key factor that greatly influences changes in the biological seasons and geographical distribution of species. In the ecological field, the BioClimatic predictor (BioClim), which is most related to the physiological characteristics of organisms, is used for vulnerability assessment. However, BioClim values are not provided other than the future period climate average values for each GCM for the Shared Socio-economic Pathways (SSPs) scenario. In this study, BioClim data suitable for domestic conditions was produced using 1 km resolution SSPs scenario detailed data produced by Rural Development Administration, and based on the data, a species distribution model was applied to mainly grow in southern, Gyeongsangbuk-do, Gangwon-do and humid regions. Appropriate habitat distributions were predicted every 30 years for the base years (1981 - 2010) and future years (2011 - 2100) of the Acer pictum subsp. mono. Acer pictum subsp. mono appearance data were collected from a total of 819 points through the national natural environment survey data. In order to improve the performance of the MaxEnt model, the parameters of the model (LQH-1.5) were optimized, and 7 detailed biolicm indices and 5 topographical indices were applied to the MaxEnt model. Drainage, Annual Precipitation (Bio12), and Slope significantly contributed to the distribution of Acer pictum subsp. mono in Korea. As a result of reflecting the growth characteristics that favor moist and fertile soil, the influence of climatic factors was not significant. Accordingly, in the base year, the suitable habitat for a high level of Acer pictum subsp. mono is 3.41% of the area of Korea, and in the near future (2011 - 2040) and far future (2071 - 2100), SSP1-2.6 accounts for 0.01% and 0.02%, gradually decreasing. However, in SSP5-8.5, it was 0.01% and 0.72%, respectively, showing a tendency to decrease in the near future compared to the base year, but to gradually increase toward the far future. This study confirms the future distribution of vegetation that is more easily adapted to climate change, and has significance as a basic study that can be used for future forest restoration of climate change-adapted species.

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.3
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• pp.208-220
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• 2019

The seasonality of leaf fall has important implications for understanding the response of trees' phenology to climate change. In this study, we quantified the leaf fall pattern with a model to estimate the timing and speed of leaf litter according to species and considered the nutrient use strategy of canopy species. In the autumns of 2015 and 2016, leaf litter was collected periodically using 36 litter-traps from the deciduous forests in Gwangneung and sorted by species. The seasonal leaf fall pattern was estimated using the non-linear regression model of Dixon. Additionally, the resorption rate was calculated by analyzing the nitrogen concentration of the leaf litter at each collection time. The leaf litter generally began in early October and ended in mid-November depending on the species. At the peak time (T50) of leaf fall, on average, Carpinus laxiflora was first, and Quercus serrata was last. The rate of leaf fall was fastest (18.6 days) for Sorbus alnifolia in 2016 and slowest (40.8 days) for C. cordata in 2015. The nitrogen resorption rates at T50 were 0.45% for Q. serrata and 0.48% for C. laxiflora, and the resorption rate in 2015 with less precipitation was higher than in 2016. Since falling of leaf litter is affected by environmental factors such as temperature, precipitation, photoperiod, and $CO_2$ during the period attached foliage, the leaf fall pattern and nitrogen resorption differed year by year depending on the species. If we quantify the fall phenomena of deciduous trees and analyze them according to various conditions, we can predict whether the changes in leaf fall timing and speed due to climate change will prolong or shorten the growth period of trees. In addition, it may be possible to consider how this affects their nutrient use strategy.

• Spatial Information Research
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• v.11 no.3
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• pp.261-274
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• 2003

The effective probability-based tile pre-fetching algorithm and the collaborative cache replacement algorithm are able to reduce the response time for user's requests by transferring tiles which will be used in advance and determining tiles which should be removed from the restrictive cache space of a client based on the future access probabilities in Web GISs(Geographical Information Systems). The Web GISs have multi-level abstracted data for the quick response time when zoom-in and zoom-out queries are requested. But, the previous pre-fetching algorithm is applied on only two-dimensional pre-fetching space, and doesn't consider expanded pre-fetching space for multi-level abstracted data in Web GISs. In this thesis, a probability-based pre-fetching algorithm for multi-level abstracted in Web GISs was proposed. This algorithm expanded the previous two-dimensional pre-fetching space into three-dimensional one for pre-fetching tiles of the upper levels or lower levels. Moreover, we evaluated the effect of the proposed pre-fetching algorithm by using a simulation method. Through the experimental results, the response time for user requests was improved 1.8%∼21.6% on the average. Consequently, in Web GISs with multi-level abstracted data, the proposed pre-fetching algorithm and the collaborative cache replacement algorithm can reduce the response time for user requests substantially.

• Korean Journal of Remote Sensing
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• v.38 no.6_2
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• pp.1691-1707
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• 2022

Cheonji Lake, the caldera of Baekdu Mountain, located on the border of the Korean Peninsula and China, alternates between melting and freezing seasonally. There is a magma chamber beneath Cheonji, and variations in the magma chamber cause volcanic antecedents such as changes in the temperature and water pressure of hot spring water. Consequently, there is an abnormal region in Cheonji where ice melts quicker than in other areas, freezes late even during the freezing period, and has a high-temperature water surface. The abnormal area is a discharge region for hot spring water, and its ice gradient may be used to monitor volcanic activity. However, due to geographical, political and spatial issues, periodic observation of abnormal regions of Cheonji is limited. In this study, the degree of ice change in the optimal region was quantified using a Landsat -5/-7/-8 optical satellite image and a Modified U-Net regression model. From January 22, 1985 to December 8, 2020, the Visible and Near Infrared (VNIR) band of 83 Landsat images including anomalous regions was utilized. Using the relative spectral reflectance of water and ice in the VNIR band, unique data were generated for quantitative ice variability monitoring. To preserve as much information as possible from the visible and near-infrared bands, ice gradient was noticed by applying it to U-Net with two encoders, achieving good prediction accuracy with a Root Mean Square Error (RMSE) of 140 and a correlation value of 0.9968. Since the ice change value can be seen with high precision from Landsat images using Modified U-Net in the future may be utilized as one of the methods to monitor Baekdu Mountain's volcanic activity, and a more specific volcano monitoring system can be built.

• Korean Journal of Remote Sensing
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• v.39 no.6_1
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• pp.1255-1272
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• 2023

Satellite-based chlorophyll-a concentration, produced as a long-term time series, is crucial for global climate change research. The production of data without gaps through the merging of time-synthesized or multi-satellite data is essential. However, studies related to satellite-based chlorophyll-a concentration in the waters around the Korean Peninsula have mainly focused on evaluating seasonal characteristics or proposing algorithms suitable for research areas using a single ocean color sensor. In this study, a merging dataset of remote sensing reflectance from the geostationary sensor GOCI-II and polar-orbiting sensors (MODIS, VIIRS, OLCI) was utilized to achieve high spatial coverage of chlorophyll-a concentration in the waters around the Korean Peninsula. The spatial coverage in the results of this study increased by approximately 30% compared to polar-orbiting sensor data, effectively compensating for gaps caused by clouds. Additionally, we aimed to quantitatively assess accuracy through comparison with global chlorophyll-a composite data provided by Ocean Colour Climate Change Initiative (OC-CCI) and GlobColour, along with in-situ observation data. However, due to the limited number of in-situ observation data, we could not provide statistically significant results. Nevertheless, we observed a tendency for underestimation compared to global data. Furthermore, for the evaluation of practical applications in response to marine disasters such as red tides, we qualitatively compared our results with a case of a red tide in the East Sea in 2013. The results showed similarities to OC-CCI rather than standalone geostationary sensor results. Through this study, we plan to use the generated data for future research in artificial intelligence models for prediction and anomaly utilization. It is anticipated that the results will be beneficial for monitoring chlorophyll-a events in the coastal waters around Korea.