• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.321-321
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• 2022

유역 모델링은 유역에 강우의 유출 과정을 재현할 수 있는 과정이다. 과거 유역 모델링은 1차원 수준에서 유출과정을 모의하는데 그쳤으나, 기술이 발전함에 있어 입력하는 매개변수 수가 증가함에 따라 모의값의 신뢰성이 높아지고 있다. 본 연구에서는 다양한 매개변수 중 공간매개변수로써 널리 활용되고 있는 수치표고모델의 신뢰성과 범용성을 확인하고자 한다. 유역모델링 연구에 있어, 수치표고모델 정확성은 결과값의 신뢰성을 좌우하는 중요한 인자 중 하나이다. 수치표고모델이란 실제 지형이 나타내는 표고 정보를 수치화 하여 격자 안에 담은 형태의 파일로 대표적으로 DEM(Digital Elevation Models)과 DSM(Digital Surface Models)로 나눌 수 있다 DEM의 경우 해당 지형의 고도정보만을 담고있으며, DSM은 지표면 상의 나무, 건물 등 포함한 지표면의 고도를 담고 있다. 현재 NASA에서는 전 지구의 30m격자 크기로 SRTM-DSM을 제공하고 있으며, 우리나라 국토지리정보원에서도 90m 격자크기의 DEM을 제공하고 있다. 본 연구에서는 남한강 유역의 수치표고모델을 세 가지 Case로 나눠서 유출량 변화 검토를 진행하였다. 산지가 많은 남한강 유역의 10개의 소유역을 선정하였고, 다음과 같이 3개의 Case를 적용하였다. Case1, DEM 자료를 입력했을 경우, Case2, DSM 자료를 입력했을 경우, Case3 DSM+DEM 자료를 입력했을 경우, 각 Case에 대해 유출량을 산정하였고, 그 결과값을 분석하였다. 해당 유역에 세 가지 Case 모두 유출량의 변화량의 큰 차이를 보이지 않았으며, 공간매개변수 적용에 있어 타당성을 보였다. 따라서 본 연구는 인공위성을 통해 산출된 수치표고모델의 신뢰성을 확인 하였고, 활용가능성을 검토 하였다. 이에 따라 향후 연구에 수치표고모델 적용에 있어 미계측유역에도 활용가능한 연구로 기여할 수 있을 것으로 판단된다.

• Journal of Korea Water Resources Association
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• v.44 no.6
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• pp.439-447
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• 2011

This study aims to test the feasibility of combined use of EFDC (Environmental Fluid Dynamics Code) hydrodynamic model and WASP7.3 (Water Quality Analysis Program) model to improve accuracy of water quality predictions of the Yongdam Lake, Korea. The orthogonal curvilinear grid system was used for EFDC model to represent riverine shape of the study area. Relationship between volume, surface and elevation results were checked to verify if the grid system represents morphology of the lake properly. Monthly average boundary water quality conditions were estimated using the monthly monitored water quality data from Korean Ministry of Environment DB system. Monthly tributary flow rates were back-routed using dam discharge data and allocated in proportion to each basin area as direct measurements were not available. The optimum number of grid system was determined to be 372 horizontal cells and 10 vertical layers of the site for 1 year simulation of hydrodynamics and water quality out of iterative trials. Monthly observed BOD, TN, TP and Chl-a concentrations inside the lake were used for calibration of WASP7.3 model. This study shows that EFDC and WASP can be used in series successfully to improve accuracy in water quality modeling. However, it was observed that the amount of data to develop inflow water quality and flow rate boundary conditions and water quality data inside lake for calibration were not enough for accurate modeling. It is suggested that object-oriented data collection systems would be necessary to ensure accuracy of EFDC-WASP model application and thus for efficient lake water quality management strategy development.

• Restorative Dentistry and Endodontics
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• v.45 no.1
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• pp.6.1-6.8
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• 2020

Objectives: This study investigated the effects of a hydrofluoric acid (HA; solution of hydrogen fluoride [HF] in water)-based smart etching (SE) solution at an elevated temperature on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics in terms of bond strength and morphological changes. Materials and Methods: Eighty sintered Y-TZP specimens were prepared for shear bond strength (SBS) testing. The bonding surface of the Y-TZP specimens was treated with 37% phosphoric acid etching at 20℃-25℃, 4% HA etching at 20℃-25℃, or HA-based SE at 70℃-80℃. In all groups, zirconia primers were applied to the bonding surface of Y-TZP. For each group, 2 types of resin cement (with or without methacryloyloxydecyl dihydrogen phosphate [MDP]) were used. SBS testing was performed. Topographic changes of the etched Y-TZP surface were analyzed using scanning electron microscopy and atomic force microscopy. The results were analyzed and compared using 2-way analysis of variance. Results: Regardless of the type of resin cement, the highest bond strength was measured in the SE group, with significant differences compared to the other groups (p < 0.05). In all groups, MDP-containing resin cement yielded significantly higher bond strength values than MDP-free resin cement (p < 0.05). It was also shown that the Y-TZP surface was etched by the SE solution, causing a large change in the surface topography. Conclusions: Bond strength significantly improved when a heated HA-based SE solution was applied to the Y-TZP surface, and the etched Y-TZP surface was more irregular and had higher surface roughness.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.215-219
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• 2005

A macro spreadsheet model, WEANES (Wet Pond Annual Efficiency Simulation Model), has been developed to predict the long-term or annual removal efficiencies of wet retention/detention basins. The model uses historical, site-specific, multi-year, rainfall data, usually available from a nearby National Oceanic and Atmospheric Administration (NOAA) climatological station to estimate basin efficiencies which are calculated based on annual mass loads. Other required input parameters are: 1) watershed parameters; drainage area, pervious curve number, directly connected impervious area, and ti me of concentration, 2) pond parameters; control and overflow elevations, pond side slopes, surface areas at control elevation and pond bottom; 3) outlet structure parameters; 4) pollutant event mean concentrations; and 5) pond loss rate which is defined as the net loss due to evaporation, infiltration and water reuse. The model offers default options for parameters such as pollutant event mean concentrations and pond loss rate. The model can serve as a design, planning, and permitting tool for consulting engineers, planners and government regulators.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.624-628
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• 2008

Two-dimensional flow analysis is a way to provide good estimates for complex flow features in flow around islands and obstructions, flow at confluence and flow in braided channel. One of difficult problems to develop a two-dimensional hydraulic model is to analyze dry and wet area in river channel. Dry/wet problem can be encountered in river and coastal engineering problems, such as flood propagation, dam break analysis, tidal processes and so on. The objective of this study is to develop an accurate and robust two-dimensional finite element method with dry/wet technique in complex natural rivers. The dry/wet technique with Deforming Grid Method was developed in this study. The Deforming Grid Method was used to construct new mesh by eliminating of dry nodes and elements. The eliminated nodes and elements were decided by considering of the rising/descending velocity of water surface elevation. Several numerical simulations were carried out to examine the performance of the Deforming Grid Method for the purpose of validation and verification of the model in rectangular and trapezoidal channel with partly dry side. The application results of the model were displayed reasonable flow distribution.

• Journal of Wetlands Research
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• v.8 no.1
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• pp.73-82
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• 2006

In this study, the hydraulic channel routing model is applied to analyze water surface elevation pattern on the Nakdong river in flood cases. The procedure to apply FLDWAV model is presented to solve the Saint-Venant Equations by using four points implicit finite differential scheme. And the flood travel time is studied for reasonable dam management. As this results, variable assumption and constraint are followed to evaluate flood travelling time by hydraulic model. A guideline of reasonable dam's decision making considering downstream effect is showed by this constructed model, and scientific hydraulic analysis is possible by it.

• Journal of Korea Water Resources Association
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• v.55 no.10
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• pp.835-841
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• 2022

The water level of the dam reservoir is an important data in the operation of the dam. reservoir storage can be calculated by using water levels or prepared for disasters such as drought and floods. However, the water level is measured near the dam, making it difficult to represent a reservoir with a large area, and there is a high possibility that the water surface will be distorted due to discharge. Furthermore, the results of the survey showed that the water level of the reservoir is irregular rather than constant, and the water level of the reservoir is repeatedly falling and rising by section. In order to calculate such a complex and irregular representative water level, the water level observation density of the reservoir must be increased. In this study, we tried to derive the optimum water level observation density for Hwacheon Dam. A reasonable water level measurement density was derived by investigating the water level elevation of the reservoir and statistically analyzing it. The observation density may vary depending on the size of the reservoir, so the same analysis was conducted on the Goesan Dam and Boseonggang Dam. According to the results, four Hwacheon dams, three Goesan dams, and seven Boseong River dams are needed for observation density.

• Journal of Korea Soil Environment Society
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• v.1 no.2
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• pp.15-21
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• 1996

Effects of acid deposition on the acidification of surface water over a short term period were studied during June~October, 1995. A reservoir located in Chunchon, Kangwondo was selected for this study because this reservoir had received little man-made pollutants. Geological survey within the study area was carried out and the pH of a small and shallow stream flowing from the mountain valley down to the reservoir was monitored. Rainfall was measured by using a rain gauge and the precipitation was collected by automatic precipitation sampler. During the study period, rain pH was in the range of 3.81~5.77 with an average of 4.8. The EC was in the range of 5~189$\mu$S/cm with an average of 10.6$\mu$S/cm. ionic composition of the rainfall showed that of the anions, deposition of ${SO_4}^{2-}$, was highest with 3,119.7 kg/$\textrm{km}^2$, and it was $NH^{4+}$ with 1,053.2kg/$\textrm{km}^2$ for cations. The surface water pHs were maintained neutral or weak basic representing little evidence of acidification regardless of the acidic rainfall pH. Every time of sampling, however, the pHs exhibited increasing tendency as elevation of measuring site of the stream became lowered, which indicated the impacts of acid-base reactions by acidic or basic substances during travel of water downstream. This result suggested the necessity of further research to determine the respective buffering capacity of soil and underlying rocks.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.30-38
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• 2009

In recent years, there's been strong demand for coastal structures that have a permeability that serves water affinity and disaster prevention from wave attack. The aim of this study is to examine the wave transformation, including wave run-up that propagates over the coastal structures with a steep slope. A numerical model based on the nonlinear shallow water equation, together with the unsteady nonlinear Darcy law for fluid motion in permeable underlayer and laboratory measurements was carried out in terms of the free surface elevations and fluid particle velocities for the cases of regular and irregular waves over 1:5 impermeable and permeable slopes. The numerical results were used to evaluate the application and limitations of the PBREAK numerical model. The numerical model could predict the cross-shore variation of the wave profile reasonably, but showed less accurate results in the breaking zone that the mass and momentum influx is exchanged the most. Except near the wave crest, the computed depth averaged velocities could represent the measured profile below the trough level fairly well.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.470-470
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• 2015

본 연구의 목적은 위성영상 기반의 SEBAL(Surface Energy Balance Algorithm for Land) 모형과 SWAT(Soil and Water Assessment Tool) 수문모형을 용담댐 유역($922.3km^2$)에 적용하여 증발산량을 산정하고 모형 간 공간 증발산량의 비교를 통해 각 모형의 적용성을 평가하는데 있다. 이를 위해 SEBAL모형의 입력자료로 Terra MODIS(Moderate Resolution Imaging Spectrometer) Product 중 Normalized Distribution Vegetation Index(NDVI), Albedo 영상을 2012년부터 2013년까지 월단위로 구축하고, 일단위의 Land Surface Temperature(LST) 영상을 구축하였다. 지형자료로는 Digital Elevation Model(DEM)과 Land use를 구축하였으며 SEBAL 모형의 구동을 위한 위성영상 및 지형자료는 500 m의 공간해상도로 재구축하였다. SWAT 모형의 모의를 위해 기상 및 유량 자료를 2000년부터 2013년까지 일단위로 구축하였고, DEM, Land use, 토양도의 지형자료를 30 m의 공간해상도로 구축하였다. SWAT 모형의 유출 검보정 후 수위관측소 지점에서 평균 $R^2$를 산정한 결과 도치(0.80), 동향(0.72), 석정(0.64), 주천(0.80), 천천(0.80), 용담댐(0.72)로 높은 상관성을 나타냈으며, 유출 검보정 후 SWAT 모형의 증발산량 모의 결과를 바탕으로 SEBAL 모형과의 공간 증발산량을 비교하였다. 두 모형의 증발산량은 SEBAL 모형의 경우 지형에 따라 SWAT 모형은 토양 특성에 따라 분포하는 경향이 다르게 나타났다. SEBAL 모형은 주로 저지대에서 증발산량이 높게 산정되며 고지대로 갈수록 감소하여 증발산량이 지형의 고저차에 따라 분포하는 모습을 보였다. SWAT 모형은 토양 특성에 따라 증발산량이 분포하며 유역 내에서 뚜렷한 차이를 나타내지는 않았다. 월별 총 증발산량은 SWAT 모형의 경우 7~8월에 약 90 mm/mon로 가장 높게 나타나고 1~2월은 0 mm/mon로 계절별 변화폭이 컸으나, SEBAL 모형의 경우 5~6월에 증발산량이 약 60 mm/mon로 가장 높게 나타났고 계절별 변화 폭이 SWAT 모형에 비해 적은 모습을 보였다. 이는 위성영상을 기반으로 하는 SEBAL 모형의 특성상 장마 기간에 해당하는 7~8월은 구름으로 인해 일사량이 적게 계산되고, 그 결과 5~6월에 비해 증발산량이 작게 산정되는 것으로 판단된다.