• Atmosphere
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• v.32 no.4
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• pp.395-409
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• 2022

A new soil moisture initialization scheme is applied to the Korea Meteorological Administration (KMA) Global Seasonal forecasting system version 6 (GloSea6). It is designed to ingest the microwave soil moisture retrievals from Soil Moisture Active Passive (SMAP) radiometer using the Local Ensemble Transform Kalman Filter (LETKF). In this technical note, we describe the procedure of the newly-adopted initialization scheme, the change of soil moisture states by assimilation, and the forecast skill differences for the surface temperature and precipitation by GloSea6 simulation from two preliminary experiments. Based on a 4-year analysis experiment, the soil moisture from the land-surface model of current operational GloSea6 is found to be drier generally comparing to SMAP observation. LETKF data assimilation shows a tendency toward being wet globally, especially in arid area such as deserts and Tibetan Plateau. Also, it increases soil moisture analysis increments in most soil levels of wetness in land than current operation. The other experiment of GloSea6 forecast with application of the new initialization system for the heat wave case in 2020 summer shows that the memory of soil moisture anomalies obtained by the new initialization system is persistent throughout the entire forecast period of three months. However, averaged forecast improvements are not substantial and mixed over Eurasia during the period of forecast: forecast skill for the precipitation improved slightly but for the surface air temperature rather degraded. Our preliminary results suggest that additional elaborate developments in the soil moisture initialization are still required to improve overall forecast skills.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.445-460
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• 2011

The objective of this study was to construct and assess the applicability of the EFDC model for Saemangeum Reservoir as a 3D hydrodynamic and water quality modeling tool that is necessary for the effective management of water quality and establishment of conservation measures. The model grids for both reservoir system only and reservoir-ocean system were created using the most recent survey data to compare the effects of different downstream boundary conditions. The model was applied for the simulations of temperature, salinity, water quality variables including chemical oxygen demand (COD), chlorophyll-a (Chl-a), phosphorus and nitrogen species and algal biomass, and validated using the field data obtained in 2008. Although the model reasonably represented the temporal and spatial variations of the state variables in the reservoir with limited boundary forcing data, the salinity level was underestimated in the middle and upstream of the reservoir when the flow data were used at downstream boundaries; Sinsi and Garyuk Gates. In turn, the error caused to increase the bias of water quality simulations, and inaccurate simulation of density flow regime of river inflow during flood events. It is likely because of the loss of momentum of sea water intrusion at downstream boundaries. In contrast to flow boundary conditions, the mixing between sea water and freshwater was well reproduced when open water boundary condition was applied. Thus, it is required to improve the downstream boundary conditions that can accommodate the real operations of the sluice gates.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.3
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• pp.39-47
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• 2002

This paper deals with study of a new framework for the traceback of distributed DoS(Denial of Service) attacks in the Internet, in which many sources flood "spoofed" IP packets towards a single victim. In our scheme, the destination host traces those anonymous packets' losses, and infers the logical end-to-end paths back towards the sources. This method is based on the fact that there is a strong correlation between packet losses when those packets traverse along a same route, and the simulation results show high probabilities of detecting the topology under a certain condition. Compared with previous approaches, our scheme has a number of distinct features: It can be performed in realtime or non-realtime, without any supports of routers or ISPs. Our results may be applied to the inference of physical topology and to support previous approaches.pproaches.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.329-329
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• 2021

우리나라의 농촌유역은 일반적으로 상류의 농업용저수지와 하류의 배수장을 통해 홍수조절이 이루어지며, 각 농업수리구조물의 운영이 유역의 홍수 및 침수 발생에 큰 영향을 끼친다. 농촌유역의 홍수 대응 능력을 향상시키기 위해서는 농업수리구조물의 통합적 운영이 필요하나 현실에서 이를 시험 운영하기 위해서는 시간적·경제적으로 한계가 있다. 따라서 농촌유역 내 농업수리구조물을 연계한 통합 해석 시스템을 활용하여 다양한 구조물 운영 시나리오에 따른 홍수 위험을 예측하고 효율적인 대응 방안을 마련할 필요가 있다. 본 연구에서는 농업수리구조물을 연계한 홍수·침수 모의 시스템을 구축하기 위하여, 농촌유역에서 홍수·침수 모의를 위한 요소별 모듈을 구성하고, 각 모듈의 연계 기술을 개발하였다. 홍수·침수 해석 모듈은 농업용저수지 상류 유역에서부터 하류 하천 및 농경지까지 통합적으로 분석할 수 있도록 강우 분석 모듈, 강우-유출 모듈, 저수지 운영 모듈, 하천 수위 모듈, 농경지 배수 모듈의 5가지로 구성하였으며, 데이터베이스 모듈을 통해 기초자료를 저장하고 모듈 간의 입출력 과정을 처리하였다. 강우 분석, 강우-유출, 농경지 배수 모듈은 python 코드를 기반으로 자체적으로 구축하였으며, 기존의 모형 (FARD, HEC-HMS, GATE2018)들과 비교한 결과 거의 동일한 모의 결과를 나타냈다. 저수지 운영 모듈과 하천 수위 모듈은 각각 미 공병단의 HEC-5, HEC-RAS 모형을 CLI (Command Line Interface) 방식으로 외부 구동하도록 구성하였다. 전체 모듈 간의 연계에는 python 라이브러리인 Dask를 적용하여 대량의 데이터에 대한 병렬 처리 구조를 갖춤으로써 다양한 기상자료와 운영 시나리오에 따른 반복 작업을 효율적으로 수행하도록 구성하였다. 본 연구에서 개발한 홍수·침수 모의 요소별 모듈과 연계 기술을 기반으로, 농업수리구조물의 연계 운영을 통합적으로 모의함으로써 홍수 대비를 위한 효율적인 구조물 운영안을 도출할 수 있을 것으로 기대된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.391-391
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• 2020

본 연구의 목적은 2006년 6월 ~ 10월에 발생한 메콩강 하류 지역의 홍수를 모의하는 것이다. 강우자료는 위성강우 자료인 미국 NOAA의 CMORPH를 적용하였으며, 홍수유출 해석은 GRM 모델을 적용하였다. Tonlesap 호수를 포함하는 메콩강 하류 지역의 침수분석은 G2D 모델을 적용하였다. 위성강우 자료는 NOAA의 3시간 간격의 CMORPH 위성강우자료를 일일강우량 자료로 변환하고, 일본의 Research Institute for Humanity and Nature (RIHN)과 Meteorological Research Institute of the Japan Meteorological Agency (MRI/JMA)의 APHRODITE 프로젝트에 의해 구축된 APHRODITE 강우량 자료를 이용하여 보정한 후 홍수모의에 적용하였다. DEM 자료는 HydroSHED 15s자료를 이용하였고, 토양도는 UN FAO의 HWSD, 그리고 토양도는 Global map landcover ver3.0을 이용하였다. GRM 모델과 G2D 모델은 Github(https://github.com/floodmodel)에 공개되어 있으며, 이를 이용하였다. 유출 모델은 메콩강 전체 유역을 대상으로 2682.815m의 공간해상도로 구축하였다. 보정한 강우를 이용하여 유출모의 한 결과 첨두유량은 23,796.8 ㎥/sec로 계산되었다. Kratie 지점의 유출량과 Tonlesap 호수로 집수되는 유량을 상류단 경계조건으로 이용하여 약 150일 동안의 침수모의를 하였다. 450 m 공간해상도로 침수모의 도매인을 구축하였으며, 조도계수는 0.045를 사용하였고, 하류단은 자유수면 유출조건을 적용하였다. 침수분석 결과 메콩강 본류를 흐르는 유량이 Tonlesap 호수로 유입되어 호수의 수위가 상승하였다. Tonlesap 호수의 최대침수심은 약 11 m를 나타내었으며, 호수로 유입된 유량은 모의기간 중에 호수에 저류되어 있었다. 메콩강 본류의 Kratie 지점으로 유입되는 유량이 첨두값을 지난 후에도 모의 기간이 길어질수록 메콩강 하류 델타지역과 그 주변의 평지로 침수범위가 확대 되었다. 모의 종료시에는 메콩강 하류가 광범위하게 침수되면서 최대 침수면적을 나타내었다. 본 연구에서 메콩강을 범람한 홍수는 메콩강 하류의 서쪽 해안으로 먼저 유출이 되었다. 이는 침수모의에 적용된 DEM 자료가 북동쪽에서 서남쪽 방향으로 빗살무늬 형태의 고도분포를 가지기 때문인 것으로 판단되며, 대상 지역의 DEM 정확성 평가와 함께 추가적인 연구가 필요하다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.156-156
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• 2021

본 연구는 지역빈도해석을 기반으로한 인공신경망 모델과 기존에 널리 사용되는 방법인 홍수지수법의 성능을 몬테카를로 시뮬레이션을 이용하여 평가하였다. 컴퓨터 기술이 발달함에 따라 인공지능에 대한 접근성이 좋아지며 수문학을 포함한 다양한 분야에 적용되고 있다. 인공지능을 이용하여 강수량 및 유량 등 다양한 수문자료에 대한 예측이 이루어지고 있으나 빈도해석에 관한 연구는 비교적 적다. 본 연구에서 사용된 인공 지능 모델은 대상 지점의 지형학적 자료와 수문학적 자료를 이용하여 인공신경망을 통해 지점의 확률강우량(QRT-ANN) 및 확률분포형의 매개변수 (PRT-ANN)를 추정한다. 지형학적 자료로는 위도, 경도 그리고 고도가 사용되었으며 수문학적 자료로는 대상 지점의 최근 30년 일일연최대강우량을 사용하였다. 지역빈도해석의 정확도는 지역 내 통계적 특성이 비슷한 지점들이 포함되면 될수록 높아진다. 통계적 특성으로는 불일치 척도, 이질성 척도, 적합성 척도가 있으며 다양한 조건의 통계적 특성에 따른 세 개의 지역빈도해석 방법의 성능을 평가하고자 하였다. 대상 지역 내 n개의 지점이 있다고 가정하였을 때, 홍수지수법의 경우 n-1개의 지점으로 추정한 지역 성장곡선을 이용하여 나머지 1개 지점의 확률강우량을 산정할 수 있으며 인공신경망 모델들 또한 n-1개 지점들의 자료를 이용하여 모델을 구축한 뒤 나머지 지점의 확률강우량 및 확률분포형의 매개변수를 예측할 수 있다. PRT-ANN의 경우 예측된 매개변수를 이용하여 확률강우량을 산정하며 시뮬레이션 시행마다 발생시킨 자료의 지점빈도해석 결과에 대한 나머지 세 방법의 평균 제곱근 상대오차 (Relative root mean square error, RRMSE)를 계산하였다. 몬테카를로 시뮬레이션을 이용한 성능 분석을 통하여 관측값의 다양한 통계적 특성에 맞는 지역빈도해석 방법을 제시할 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.157-157
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• 2022

Recent decades have seen all over the world increasing drought in some regions and increasing flood in others. Climate change has been alarming in many regions resulting in degradation and diminution of available freshwater. The effect of global warming and overpopulation associated with increasing irrigated farming and valuable agricultural lands could be particularly disastrous for coastal areas like the one of Benin. The coastal region of Benin is under a heavy demographic pressure and was in the last decades the object of important urban developments. The present study aims to roughly study the general effect of climate change (Sea Level Rise: SLR) and groundwater pumping on Seawater intrusion (SWI) in Benin's coastal region. To reach the main goal of our study, the region aquifer system was built in numerical model using SEAWAT engine from Visual MODFLOW. The model is built and calibrated from 2016 to 2020 in SEAWAT, and using WinPEST the model parameters were optimized for a better performance. The optimized parameters are used for seawater intrusion intensity evaluation in the coastal region of Benin The simulation of the hydraulic head in the calibration period, showed groundwater head drawdown across the area with an average of 1.92m which is observed on the field by groundwater level depletion in hand dug wells mainly in the south of the study area. SWI area increased with a difference of 2.59km² between the start and end time of the modeling period. By considering SLR due to global warming, the model was stimulated to predict SWI area in 2050. IPCC scenario IS92a simulated SLR in the coastal region of Benin and the average rise is estimated at 20cm by 2050. Using the average rise, the model is run for SWI area estimation in 2050. SWI area in 2050 increased by an average of 10.34% (21.04 km²); this is expected to keep increasing as population grows and SLR.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.5
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• pp.25-35
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• 2023

The estuary reservoir is a major source of agricultural water in Korea; for effective and sustainable water resource management of the estuary reservoir, it is crucial to comprehensively consider various water resource factors, including water supply, flood, and pollutant management, and analyze future runoff changes in consideration of environmental changes such as climate change. The objective of this study is to estimate the impact of future climate change on the runoff characteristics of an estuary reservoir watershed. Climate data on future Shared Socioeconomic Pathway (SSP) scenarios were derived from two Global Climate Models (GCMs) of the Coupled Model Intercomparison Project phase 6 (CMIP6). The Hydrological Simulation Program-Fortran (HSPF) was used to simulate past and future long-term runoff of the Ganwol estuary reservoir watershed. The findings showed that as the impact of climate change intensified, the average annual runoff in the future period was higher in the order of SSP5, SSP3, SSP1, and SSP2, and the ratio of runoff in July decreased while the ratio of runoff in October increased. Moreover, in terms of river flow regime, the SSP2 scenario was found to be the most advantageous and the SSP3 scenario was the most disadvantageous. The findings of this study can be used as basic data for developing sustainable water resource management plans and can be applied to estuary reservoir models to predict future environmental changes in estuary reservoirs.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.4
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• pp.133-144
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• 2006

It is investigated using ADCIRC model to find an optimal gate operation in order to maintain target water level of the inner Saemangeum Reservoir. Various developing procedures and river inflows conditions are considered in modeling. For the gate operations, consecutive openings to inflow and outflow, such as once a day, twice a day and once per two days are considered. However water level increases gradually due to river inflows regardless of gate operations. In order to maintain target level 0.0 m, it is recommended to shut down of gate in order to prevent inflows of outer sea water at least once per 6 days for normal riverine inflows and once per 3 days for flood inflows during consecutive operations. Then it is balanced within maximum of ${\pm}0.4m$ of deviations from target level of 0.0 meter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6B
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• pp.589-598
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• 2010

When the hydraulic structures, such as bridge and weir, are consecutively installed to a short section of a river with complicated cross section, analyzing the flow characteristics and the riverbed change modality of the river is very important. In the 250 m section of the Taehwa river near the Samho-bridge, which passes through Ulsan city, three bridges has been installed, and the tributary water is flowing into both up and downstream of the section. Due to these factors, when the flood occurs, the cross section of the river changes vastly by the water level change and scour. Even so, due to the fact that the Samho-bridge divides the section into two parts, the national river and the regional river, each part is being analyzed separately by the onedimensional model. In this study, the flow characteristics due to the bridge concentration and the tributary water inflow were jointly analyzed for both up and downstream by using the one-dimensional HEC-RAS model and the two-dimensional SMS model, such as RMA2. The riverbed change modality of the section was also investigated by using the SED2D model. The results showed that the water level difference between the HEC-RAS and RMA2 was 0.87 m when applied to the three consecutive bridges. The riverbed change simulation using SED2D showed that the maximum scour was 0.231 m and it occurred at the Samho-bridge, which located in the middle and has short pier distance. In conclusion, when planning the river maintenance for the regions with concentrated bridges or the sections with severe changes in cross-section and flow, estimating the flood elevation by two-dimensional model and establishing countermeasures for the scouring of the bridge are required. In addition, an integrated analysis on both the national river and the regional river is necessary.