• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.3
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• pp.321-331
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• 2008

A model has been constructed in this study for the investigation of physical characteristics of the Gyeonggi Bay and Han River estuary. MIKE 21 HD (HyDrodynamics) has been used for the uncertainty analysis of the tide of the Gyeonngi Bay and Han River estuary. A total of 15 model experiments have been performed for the hydrodynamic parts and the analysis of results have been made in terms of RMSD (Root-mean square deviation) which has been frequently employed in the suitability analysis of hydrological data since the introduction by NERC(1975), U.K. A smaller value of RMSD indicates the more suitability of a parameter to the model. Analysis of the hydrodynamic results has shown that RMSD of the mean tidal range has the largest value of 0.1148 at Yeomha channel while has the smallest value of 0.0400 at Yeonphyong-do, indicating that the uncertainty in the mean tidal range on near-shore side is larger than that of offshore side. Experiment with reduced water depth by 10% has produced a most significant increase in RMSD. It is therefore implied that the model response changes more sensitively to water depth rather than grid sizes, open boundary forcing and river discharge.

• Korean Journal of Remote Sensing
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• v.36 no.5_1
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• pp.749-762
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• 2020

Precipitation is closely related to various hydrometeorological phenomena, such as runoff and evapotranspiration. In Korean Peninsula, observing rainfall intensity using weather radar and rain gauge network is dominating due to their accurate, intuitive and precise detecting power. However,since these methods are not suitable at ungauged regions, rainfall detection using satellite is required. Satellite-based rainfall data has coarse spatial resolution (10 km, 25 km), and has a limited range of usage due to its reliability of data. The aim of this study is to obtain finer scale precipitation. Especially, to make the applicability of satellite higher at ungauged regions, 10 km satellite-based rainfall data was downscaled to 1 km data using MODerate Resolution Imaging Spectroradiometer (MODIS) based cloud property. Downscaled precipitation was verified in urban region, which has complex topographical and environmental characteristics. Correlation coefficient was similar in summer (+0), decreased in spring (-0.08) and autumn (-0.01), and increased in winter (+0.04) season compared to Global Precipitation Measurement (GPM) based precipitation. Downscaling without calibration using in situ data could be useful in areas where rain gauge system is not sufficient or ground observations are rarely available.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.407-418
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• 2017

Due to geographical features of being close to DPRK (Democratic People's Republic of Korea), the Imjin River basin has difficulties in hydrological observation, and is vulnerable to unexpected flood occurrence. As a countermeasure, Gunnam Flood Control Reservoir construction was planned in 2005. Despite such a structural measure, damages by DPRK's illegal release continues to occur. Futhermore the Imjin River's flow has been decreased due to the effect of continuous drought in the Korean Peninsula since 2012 and DPRK's unilateral storage of water. A new operation method is derived for the Gunnam Flood Control Reservoir in order to cope with drought damages on the Imjin River basin and to ensure efficient response time upon flooding. The operation method maintaining Gunnam Flood Control Reservoir's water level by raising from EL.23.0 m to EL.31.0 m during the flood season for securing reservoir capacity enables to secure additional $14,000,000m^3$ water compared to the existing operation methods. The operation method to store inflow by controlling release to $250m^3/s$ in the early stage of flood has increased 2.66% on average in terms of detention effect of reservoir compared to the existing operation methods. The method enables to secure 19 hours to prepare flood compared to the existing methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1B
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• pp.29-36
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• 2011

Evapotranspiration (ET) from the various surfaces needs to be understood because it is a crucial hydrological factor to grasp interaction between the land surface and the atmosphere. A traditional way of estimating it, which is calculating it empirically using lysimeter and pan evaporation observations, has a limitation that the measurements represent only point values. However, these measurements cannot describe ET because it is easily affected by outer circumstances. Thus, remote sensing technology was applied to estimate spatial distribution of ET. In this study, we estimated major components of energy balance method (i.e. net radiation flux, soil heat flux, sensible heat flux, and latent heat flux) and ET as a map using Mapping Evapo-Transpiration with Internalized Calibration (METRIC) satellite-based image processing model. This model was run using Landsat imagery of Gyeongan watershed in Korea on Feb 1, 2003 and Sep 13, 2006. Basic statistical analyses were also conducted. The estimated mean daily ETs had respectively 22% and 11% of errors with pan evaporation data acquired from the Suwon Weather Station. This result represented similar distribution compared with previous studies and confirmed that the METRIC algorithm had high reliability in the watershed. In addition, ET distribution of each land use type was separately examined. As a result, it was identified that vegetation density had dominant impacts on distribution of ET. Seasonally, ET in a growing season represented significantly higher than in a dormant season due to more active transpiration. The ET maps will be useful to analyze how ET behaves along with the circumstantial conditions; land cover classification, vegetation density, elevation, topography.

• Journal of Korea Water Resources Association
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• v.48 no.3
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• pp.149-158
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• 2015

It is well known that emergency outlet works have to be provided for the safety of dams. However, concept of emergency outlet works did not applied for the design of the most dams in Korea. Korean design standard for low-level outlet works does not provide enough design criteria which could be used in design of emergency outlet works. In this research, as-built status and hydraulic design criteria of outlet works, such as drawdown rate or hydraulic pressure due to the impounded water depth, were examined. Another relationship between drawdown rate and the dam slope stability was also examined with SEEP model. It was found that 25% reduction of impounded water depth decreases the pressure forces about 50%. Therefore, outlet works should be designed to drawdown properly at the beginning of the emergency. Seepage analysis of dam bodies showed that most of Korean dams could safely stand for 1m/day drawdown rate. Higher drawdown rate could result high discharge so the drawdown rate must be related with the flood risk of downstream. Finally, multi-stage design was recommended that faster discharge for the initial 25% of water depth in 7-10 days than the rest of it in 1-2 months.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.281-281
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• 2016

기후변화로 인한 기상학적 자연재해로부터 대비하고 안정적인 용수공급을 위해 유역의 다양한 수문 요소들에 대한 분석 필요성이 증가하고 있다. 계절적 강수량의 편차가 큰 우리나라는 유역 통합 물관리가 중요하며, 효율적 수자원 관리와 물안보 확보를 위해 유역내 물순환을 이해하는 것이 중요하다. 유역의 유출을 결정하는 요소들에는 강우, 증발산량, 토양 수분 및 지하수 등이 있으며, 시간적으로는 홍수와 같이 단기에 발생하는 유출과 장기적으로 발생하는 유출이 있다. 장기 유출은 단기 유출에 비해 토양내 수분량이 무시할 수 없을 정도로 영향을 미치게 되므로, 1년 이상의 장기 유출 해석을 위해서는 강우가 발생하지 않는 기간 동안의 토양 수분량 변화와 증발산 영향을 고려할 필요가 있다. K-water에서 자체 개발된 분포형 장단기유출 모델인 K-DRUM은 유역을 격자(grid)단위로 구분하고 각 셀들에 대한 매개변수는 흐름방향도, 표고분포도, 토지이용도, 토지피복도 등을 GIS처리하여 일괄 입력할 수 있도록 함으로써 매개변수 산정과정에서 문제가 되는 경험적인 요인을 제거하였다. 흐름의 구분은 얕은면 흐름, 지표하 흐름, 지하수 흐름으로 구분하여 운동파법과 선형저류법을 적용하였다. 또한 초기 토양함수 자동보정기법으로 실제의 기저유출량을 재현하여 전체적인 유출모의 정확도를 높였으며, FAO-56 Penman-Monteith법을 적용한 증발산량 산정모듈과 Sugawara et al.(1984)이 제안한 개념적 융설 및 적설모듈을 추가하였다. K-DRUM모형을 이용한 유출분석은 용담댐 시험유역을 대상으로 2013년도 1년간의 유출모의를 수행하였다. 입력자료는 용담댐 유역의 지형, 토양 및 토지특성 정보와 시단위 강우 및 기상정보(온도, 바람, 일사 등)를 활용하였다. 분석 결과, 총 관측유출량은 7,151 ㎥/s이고 총 계산유출량 $8,257m^3/s$이며, 관측유출량 대비 계산유출량은 약 115% 정도로 나타났다. 연간 총 강우량은 1303.5 mm로 유역면적 약 $930km^2$을 적용하여 유역 총 강우량을 산정하면 $14,030m^3/s$로서 관측유출량은 유역 총 강우량 대비 51%이고 계산유출량은 59% 정도로 나타났다. 즉 유역 유출율은 약 51% 수준으로 보통의 유역과 유사한 수준이다. 관측된 토양수분량과 K-DRUM 모형의 계산된 토양수분량을 비교하기 위하여 관측 토양수분량의 비율을 이용하여 비교하였다. 모의결과 토양수분은 강우에 의해 변화하며, 관측결과와 유사한 형태로 나타남을 알 수 있었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.20-26
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• 2019

Where hydraulic structures are to be installed over the entire width of a river or stream, usually a bed protection structure is to be installed. However, a local scour occurs in which the river bed downstream of the river protection system is eroded due to the influence of the upstream flow characteristics. This local scour is dominant in the flow and turbulence characteristics at the boundary of the flow direction and in the material of the bed materials, and may gradually become dangerous over time. Therefore, in this study, we compared the turbulence patterns in the local scour hole at the downstream of the river bed protection with the results of the analysis of the mobile bed experiment, and compared with the application of OpenFoam, a three dimensional numerical analysis model. The distribution of depth-averaged relative turbulence intensities along the flow direction was analyzed. In addition to this result, the stabilization of scour hole was compared with the bed shear stress and Shields parameter, and the results were compared by changing the initial turbulent flow conditions. From the results, it was confirmed that the maximum depth of generation of the three-stage was dominantly developed by the magnitude of depth-averaged relative turbulence intensity rather than the mean flow velocity. This result also suggests that design, construction or gate control are needed to control the depth-averaged relative turbulence intensities in order to reduce or prevent the local scour faults that may occur in the downstream part of the bed protection.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2B
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• pp.215-224
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• 2008

The effect of streamflow considering future land use change and vegetation index information by climate change scenario was assessed using SLURP (Semi-distributed Land-Use Runoff Process) model. The model was calibrated and verified using 4 years (1999-2002) daily observed streamflow data for the upstream watershed ($260.4km^2$) of Gyeongan water level gauging station. By applying CA-Markov technique, the future land uses (2030, 2060, 2090) were predicted after test the comparison of 2004 Landsat land use and 2004 CA-Markov land use by 1996 and 2000 land use data. The future land use showed a tendency that the forest and paddy decreased while urban, grassland and bareground increased. The future vegetation indices (2030, 2060, 2090) were estimated by the equation of linear regression between monthly NDVI of NOAA AVHRR images and monthly mean temperature of 5 years (1998-2002). Using CCCma CGCM2 simulation result based on SRES A2 and B2 scenario (2030s, 2060s, 2090s) of IPCC and data were downscaled by Stochastic Spatio-Temporal Random Cascade Model (SST-RCM) technique, the model showed that the future runoff ratio was predicted from 13% to 34% while the runoff ratio of 1999-2002 was 59%. On the other hand, the impact on runoff ratio by land use change showed about 0.1% to 1% increase.

• Journal of Korean Society of Forest Science
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• v.103 no.3
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• pp.383-391
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• 2014

Long-term changes in the hydrological characteristics of a small forest watershed were examined using a master baseflow recession curve and the measured rainfall-runoff data from the experimental forest watershed in the measured years 2003-2011. The results of the study showed that the recession coefficient of direct runoff was lower than that of baseflow. In small forested watershed, the direct flow was lower than that of large scale watershed, flow due to its shorter period of occurrence. And baseflow was similar to large scale watershed's. A regression equation $y=0.7528e^{-0.022x}$($R^2=0.8938$, range 0.3~0.8 mm) was obtained using the master baseflow recession curve for the study period and the recession coefficient was calculated as K = 0.978. Changes between master baseflow recession curve and runoff showed great association and relevance such as increasing runoff was associated with the gentle slope of master baseflow recession curve and decreasing runoff was associated with the slope of master baseflow recession curve contrary. In the later years of the study period, the slope of the master baseflow recession curve appreciably became more gentle due to increases in baseflow. This suggests that the forested experimental watershed exhibit improved structural functioning of normal flood control and reduced occurrence of water shortage problems.

• Korean Journal of Remote Sensing
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• v.30 no.1
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• pp.127-136
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• 2014

When the mouth of the Nakdong River, opens its floodgate, thousands of tons of litter should flown into the South Sea, moving towards nearby coast, thus causing serious social and economic damage. For this reason, in the present study, research was performed on one certain area in northeast coast of Geoje island, which is assumed as area damaged due to rainy season and typhoon in 2012, and research for trace of movement route was implemented by using buoy to identify characteristic of movement of floating debris caused from Nakdong River. Flows related to the movement of floating debris was also identified by analyzing ocean meteorological environment. As a result of the study, total 40 tons of litter composed of grasses and trees(or plants litter) were flown into Heungnam beach on 16th, Jul which is the rainy season. Plus, the location tracking buoy, which was dropped when the typhoon SANBA was coming, was passed by southern sea of Gadeok-do and was flown into Geoje beach 1 ~ 2 days after it was dropped. The wind direction was mostly northeasterly wind around the Geoje beach at the time the buoy and floating debris were flown into northeast coast and there was common sea surface currents which was flowing into the coast.