• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2008년도 학술발표회 논문집
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• pp.1151-1154
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• 2008

The water level data sets among hydrologic observation data are correspond to the hydraulic head for each observation point and determine flow direction. The level difference among reservoir, river, and groundwater determines groundwater flow direction, just like water flows in the downstream direction because the water level of upstream point is higher than that of downstream point. We can analyze the relationship among the components in hydrologic cycle by comparing the water level differences. This research dealt with the data from Nakdong river watershed in Gyungsangnam-Do. Three data group are used for the analysis and onr group is composed of reservoir, river, and groundwater data sets. The data sets are closely(within 10 km) located in the interested area.

• 한국물환경학회지
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• 제30권6호
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• pp.612-621
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• 2014

Physicochemical factors and the phytoplankton communities in the downstream area of Namhan-River were investigated from June 2012 to November 2013. We also assessed water quality using biological water quality indices. Total nitrogen was 2.4 mg/L, total phosphorus was 0.04 mg/L, and biological oxygen demand was 1.1 mg/L. This resulted in a level 2 (Ib, good) water quality rating. A total of 259 phytoplankton taxa were classified, consisting of 26 families, two subfamilies, 64 genera, 222 species, 32 varieties, and five formas. Bacillariophyceae dominated during a1l seasons and at all sites. The dominant species were Aulacoseira granulata, Cyclotella meneghiniana, C. stelligera, Melosira varians, Cocconeis placentula var. lineata, Nitzschia palea, N. amphibia, Cymbella minuta, and Achnanthes convergens. The diatom assemblage index for organic pollution values was level A-D, and TDI was level B-D. P-IBI at most sites was at the M (moderate) level, but TSI was at the E (eutrophic) level. Most indices dropped from upstream to downstream.

• Ecology and Resilient Infrastructure
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• 제7권4호
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• pp.345-352
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• 2020

최근 하천범람에 따른 피해를 최소화하기 위해서는 대피를 위한 선행시간을 확보하는 것이 매우 중요하다. 본 연구에서는 현재 하천에서 측정되고 있는 수위 관측 자료를 이용하여 이상호우 발생시 하류의 수위를 예측하였다. 수위 예측을 위해 다중회귀모형 및 인공신경망 모형을 섬강시험유역에 적용하였다. 다중회귀모형 및 인공신경망 모형의 학습에는 섬강시험유역의 2002년부터 2010년까지의 수위 관측 자료를 이용하였으며, 학습된 모형을 이용하여 발생 가능한 수위를 예측하였다. 모의 결과 인공신경망 수위예측모형의 결정계수는 0.991 - 0.999로 나타났으며, 다중회귀수위예측 모형의 결정계수는 0.945 - 0.990로 나타나 인공신경망을 이용한 수위예측모형이 다중회귀모형보다 좀 더 나은 예측 결과를 나타내는 것을 확인할 수 있었다. 본 연구결과는 향후 하천에서 선행시간을 확보한 홍수 예보 구축에 활용할 수 있을 것으로 판단된다.

• 한국안전학회지
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• 제33권2호
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• pp.132-137
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• 2018

Compared with general rivers, fluctuations of the water level and the river bed are severe in the tidal river. In hydro-dynamic aspect, such fluctuation gives different river-bed data to us according to observing period. The time-dependent river-bed data and pre-estimation of the Manning's roughness coefficient which is the key factor of numerical modelling induces uncertainty of evaluating the design flood level. Thus it is necessary to pay more attention to calculate the flood level at tidal rivers than at general rivers. In this study, downstream of the Imjin River where is affected by tide of the West Sea selected as a study site. From the numerical modelling, it was shown that the unsteady simulation gave considerable mitigation of the water level from the starting point to 15 km upstream compared to the steady simulation. Either making a detention pond or optional dredging was not effective to mitigate the flood level at Gugok - Majung region where is located in the downstream of the Imjin River. Therefore, a more sophisticated approach is required to evaluate the design flood level estimation before constructive measures adopted in general rivers when establishing the flood control plan in a tidal river.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2002년도 학술발표회 발표논문집
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• pp.105-108
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• 2002

In this study, flood influence analysis in the downstream of Sung-Ju dam was simulated using HEC-RAS model. Input data for the simulation was which measured water level, water velocity, stream section etc. HEC-RAS model could be applied to steady flow or gradually varied flow in natural or artificial stream. HEC-RAS model which can simulate real-time changing water level and compute water surface curve was supplied to show the standard influent amount of Sung-Ju dam. Through this study the submerged damage of Sung-Ju dam's downstream would be minimized.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.173-173
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• 2015

The flood water level in tidal river is determined by the joint effects of flood discharge and tidal water levels at downstream boundary. Due to the variable tidal boundary conditions, the evaluated design water levels associated with a certain flood event can be significantly different. To avoid determining of design water levels just by a certain tidal boundary condition and remove the influence of variability in boundary condition from the evaluation of design water levels, a probabilistic approach is considered in this study. This study focuses on the development of a method to evaluate the realistic design water levels in tidal river with taking into account the combined effects of river discharge and tidal level. The flood water levels are described by the joint probability of two driving forces, river discharge and tidal water levels. The developed method is applied to determine design water levels for the tidal reach of the Han River. An unsteady flow model is used to simulate the flow in the reach. To determine design water levels associated with a certain flood event, first, possible boundary conditions are obtained by sampling starting times of tidal level time series; then for each tidal boundary condition, corresponding peak water levels along the channel are computed; and finally, design water levels are determined by computing the expectations of the peak water levels. Two types of tides which are composed by different constituents are assumed (one is composed by $M_2$, and the other one is composed by $M_2$ and $M_2$) at downstream boundary, and two flood events with different maximum flood discharges are considered in this study. It is found that (a) the computed design water levels with two assumed tides have no significant difference for a certain flood event, though variability of peak water levels due to the tidal effect is considerably different; (b) tidal effect can reach to the Jamsil submerged weir and the effect is obvious in the downstream reach of the Singok submerged weir; (c) in the tidally affected reach, the variability of peak water levels due to the tidal effect is greater if the maximum flood discharge is smaller.

• 한국안전학회지
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• 제27권6호
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• pp.166-171
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• 2012

This study aims to analyze the hydrological characteristics of downstream areas by the dam discharge of Soyanggang dam by using HEC-RAS Model. As a result of analyzing the data of dam discharge divided into hydropeaking discharge and total discharge, it as found that the maximum hydro-peaking discharge and the maximum total discharge have been 254.4 CMS and 1567.7 CMS respectively for the past 11 years. When the hydro-peaking discharge was applied to HEC-RAS Model, there occurred some sections where the water level rapidly changed, but the velocity of moving water was quite stable in the range between 0.23 m/sec and 1.16m/sec. Besides, when the total discharge was applied to this model, the submersible bridge along the dam downstream was flooded, and in some sections, the water level increased over the flood plain. Accordingly, this study judged that it is required to necessarily consider all the influence made by an increase of Soyanggang Dam's discharge when waterfronts are installed or used at dam downstream areas.

• 한국안전학회지
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• 제35권2호
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• pp.28-33
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• 2020

Recently, the overseas construction market has been actively promoted for about 10 years, and overseas dam construction has been continuously performed. For the economic and safe construction of the dam, it is important to prepare the main dam construction plan considering the design frequency of the diversion tunnel and the cofferdam. In this respect, the prediction of river level during the rainy season is significant. Since most of the overseas dam construction sites are located in areas with poor infrastructure, the most efficient and economic method to predict the water level in dam construction is to use the upstream water level. In this study, a linear regression model, which is one of the simplest statistical methods, was proposed and examined to predict the downstream level from the upstream level. The Pyeongchang River basin, which has the characteristics of the upper stream (mountain stream), was selected as the target site and the observed water level in Pyeongchang and Panwoon gaging station were used. A regression equation was developed using the water level data set from August 22th to 27th, 2017, and its applicability was tested using the water level data set from August 28th to September 1st, 2018. The dependent variable was selected as the "level difference between two stations," and the independent variable was selected as "the level of water level in Pyeongchang station two hours ago" and the "water level change rate in Pyeongchang station (m/hr)". In addition, the accuracy of the developed equation was checked by using the regression statistics of Root Mean Square Error (RMSE), Adjusted Coefficient of Determination (ACD), and Nach Sutcliffe efficiency Coefficient (NSEC). As a result, the statistical value of the linear regression model was very high, so the downstream water level prediction using the upstream water level was examined in a highly reliable way. In addition, the results of the application of the water level change rate (m/hr) to the regression equation show that although the increase of the statistical value is not large, it is effective to reduce the water level error in the rapid level rise section. Accordingly, this is a significant advantage in estimating the evacuation water level during main dam construction to secure safety in construction site.

• 한국물환경학회지
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• 제22권6호
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• pp.1060-1067
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• 2006

Water quality in the Daecheong reservoir has been deteriorated by algal bloom due to nutrient supply from the upstream of the Daecheong reservoir after heavy rainfall. Algal bloom is propagated from eutrophicated tributary into the main body of the reservoir according to the hydrological conditions. This study is aimed to estimate the water current and temperature effect by the simulation of dam spill flow control using water quality model, CE-QUAL-W2 in 2003. Water current was resulted in nutrient transport from upstream of main reservoir and nutrients were delivered up to downstream by fast water velocity. Algal blooms occurred in stagnate zone of reservoir downstream as the current of downstream was retarded according to dam outflow control. Consequently water balance in stagnate zone triggered a rise of water temperature in summer. It affected algal bloom in the embayment of the reservoir. The simulation result by outflow control scenarios showed that spill flow augmentation induced in water body instability of stagnate zone so that water temperature declined. It could be suggested that outflow control minimize algal bloom in the downstream in the flooding season as long as water elevation level is maintained properly.

• The Korean Journal of Ecology
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• 제7권3호
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• pp.109-118
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• 1983

Near future dynamics of water qualities (nutrient concentration) of the Han River was predicted, based on a mathematical model representing the relationship between the nutrient concentration in th river wagter and environmental factors (population density, land-use types, rock compositions and nutrient accumulation) in the basin. The population density and land-use types were forecasted to change distinctly in the downstream area, especially in Seoul City area in 1985~1990 whereas any environmental factor was not expected to change its level significantly in both upstream and middle reaches areas. It was indicated by the model that the nutrients concentration in the up- and mid-streams would keep its level in future as it was, but it would increase drastially in the downstream area. For the preservation of the water qualities in the downstream at least to keep its level as it was in 1980, practical countermeasures were proposed, based on the assessment of the contribution of each environmental factor to the water qualities.