• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.157-163
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• 2011

In this study, after the target basin was divided into both overland and channel grids, the travel time from center of each grid cell to watershed's outlet was calculated based on the manning equation. Through this process, volumetric discharge was calculated according to the isochrones and finally, the direct runoff hydrograph was estimated considering watershed's hydrodynamic characteristics. Sanseong subwatershed located in main stream of Bocheong basin was selected as a target basin. The model parameters are only two: area threshold and channel velocity correction factor; the optimized values were estimated at 3,800 and 3.3, respectively. The developed model based on the tuned parameters led to well-matching results between observed and calculated hydrographs (mean of absolute error of peak discharge: 3.41%, mean of absolute error of peak time: 0.67 hr). Moreover, the analysis results regarding histogram of travel time-contribution area demonstrates that the proposed model characterizes relatively well hydrodynamic characteristics of the catchment due to effective rainfall.

• Journal of Korean Society on Water Environment
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• v.37 no.4
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• pp.263-274
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• 2021

This study presents the achievements and limitations of the voluntary-based Total Maximum Daily Load (TMDL) through statistical analysis of water quality monitoring data and performance assessments of TMDL plans implemented in the Gyeongan watershed. The results clearly showed that responsible local governments complied the allocated TMDL and the designated water quality goals were successfully achieved in the required period. This was possible because the Ministry of Environment provided innovative incentives, such as, relaxations of the existing tight land-use regulations and full-scale financial aids for constructing and operating public treatment facilities to draw local government voluntary participation. However, a couple of problems which decreased the effectiveness and efficiency of the voluntary TMDL were identified. The different TMDL implementation schedules between upstream (Yongin) and downstream (Gwangju) governments caused delay in water quality improvement and exaggerated TMDL allocation to the local development which made excessive investment in the treatment facilities. Although it is not directly related to the voluntary scheme, technical methods for establishing and assessing the water quality goals should be improved so that the effects of flow conditions on water quality are properly assessed. We expect that results of this case study contribute to developing a more effective voluntary-based scheme for the implementation of the so-called 'tributary TMDL' in the future.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.4
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• pp.33-42
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• 2019

In this study, the channel and floodplain widths are indirectly measured for three different watersheds using satellite images to reflect the shape of Korean channels in the Soil and Water Assessment Tool (SWAT) model. For measuring the channel and floodplain widths, multiple satellite images were referred to ensure the widest width of certain points. In the single channel, the widths at the multiple points were measured. Based on the measured data, the regression equations were derived to estimate the channel and floodplain widths according to watershed areas. Applying these developed equations, this study evaluated the effect of the change of channel and floodplain widths on the SWAT simulation by comparing to the measured streamflow data. The developed equations estimated larger channel width and smaller floodplain compared with those calculated in the current SWAT model. As shown in the results, there was no considerable changes in the predicted streamflow using the current and developed equations. However, the flow velocity and channel depth calculated from the developed equations were smaller than those of the current equations. The differences were caused by the effect of different channel geometries used for calculating the hydraulic characteristics. The channel geometries also affected the water quality simulation in channels because the hydraulic characteristics calculated by the channel geometries are directly related to the water quality simulation. Therefore, application of the river cross-sectional regression equation reflecting the domestic stream shape is necessary for accurate water quantity / quality and water ecosystem simulation using hydrological model.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.882-885
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• 2014

The duration and frequency of flooding and not last long, by the time climate change drought. The increased accordingly by reducing stream flow and year variation. This trend is expected to continue, and change towards a comprehensive analysis of such quantity, quality and management of water resources are managed. Flood warning system is called to perform them electronically to the management of water resources such as these to be in the organic water-related basic data acquisition, storage, processing and utilization. Can be divided into hydrological observations and flood warning systems alert system broadcast system. Hydrological observation system is the measurement from the hydrological stations (water level, rainfall, water) that can be observed hydrological status of the dam basin hydrological observation data transmitted to the central office, located at the dam monitoring and control system through a variety of networks including satellite, and the collected defined as the system that sent the K-water head office in 1 minute increments hydrological observation data. Headquartered in support of this decision. Dimensions of the dam are provided in addition to inward. Channeled through various hydrologic analysis and leveraging the data transfer. This paper looks at ways to build out hydrological observation system.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.94-94
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• 2017

지속적인 수질의 모니터링과 관리가 어려운 개발도상국의 경우, 모델링을 통한 병원균의 예측이 중요하다. Soil and Water Assessment Tool (SWAT)은 유역 모델로 병원균의 거동을 모의하는데 널리 활용된다. 하지만 SWAT이 모의하는 in-stream 모듈의 경우, 소멸, 부유, 퇴적의 단계만을 고려하여 정확도가 부족하다. 따라서 본 연구는 기존 모듈에 hyporheic exchange와 생장 단계를 추가하여 모듈의 성능 개선 및 열대 산지 유역에서의 병원균의 거동을 모의하였다. 본 연구는 몬순 기후 및 산지 지형을 가진 라오스의 Houay Pano 유역을 대상으로 대장균 (Escheichia coli, E.coli)의 거동을 2011년부터 2013년까지 일 단위로 모의하였다. 기존의 SWAT 박테리아 모듈의 경우, 소멸 단계만을 가지고 보정하였을 때 모델은 대부분 0의 값을 가졌고, 부유 및 퇴적 단계가 추가 된 후에는 우기시 대부분의 모델값이 관측값의 95% 신뢰 구간에 포함되었으나 건기에는 농도가 여전히 낮게 모의됨을 확인 할 수 있다. 건기 시 낮게 모의된 농도를 증가시키기 위해, 온도에 따른 생장 단계를 추가하였으며, 이때 생장 속도는 설정된 최소-최대 생장 온도 사이에서 최대값을 가진다. 하지만 온도에 따른 생장은 열대 기후의 특성상 전 기간에 걸쳐 동시에 증가하여 건기에만 낮게 모의된 농도를 보완하는 데는 한계가 있었다. Hyporheic exchange는 강바닥에 임시로 저장된 박테리아의 양이 특정 유량에 의해서 수계로 유입되는 현상으로, 본 연구에서는 일정한 양의 hyporheic flow를 가정하여 모의하였다. 결과적으로 Hyporheic exchange를 통해 유입되는 적은 양의 E.coli는 기존에 타당하게 모의된 우기의 농도는 그대로 유지하되, 건기에 낮게 모의된 농도는 증가시켜 기존 SWAT 모듈의 한계점을 잘 보완한 것을 확인 하였다. 결론적으로, 기존의 SWAT 모델은 건기 시 낮은 농도의 E.coli를 모의하기에 한계를 보였으며, 전 기간에 걸쳐 높은 온도를 유지하는 열대 기후에서 생장 단계는 이러한 한계를 보완하기에 적합하지 않은 것으로 판단되었다. 그러나 적은 양이 전 기간에 걸쳐 동일하게 유입되는 hyporheic exchange의 경우, 건기에 낮게 모의된 농도를 증가시켜 기존의 한계를 보완할 수 있었다.

• Ecology and Resilient Infrastructure
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• v.7 no.4
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• pp.353-365
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• 2020

In this study, the characteristics of bed elevation changes of the Nakdong River when weir gates are opened were analyzed using the Hydrologic Engineering Center-River Analysis System (HEC-RAS). The study area was 292.37 km downstream of the Gudam Bridge to the Nakdong estuary of the Nakdong River. The HEC-RAS program, which is a 1D numerical analysis model, was used to simulate bed elevation changes. Simulations were conducted under two scenarios from 2017 to 2019. Scenarios 1 and 2 were devised under the conditions of a fully opened gate and during gate installation, respectively. Results confirmed that, under the conditions of Scenario 1, deposition occurred in most sections from the Hapcheon-Changnyeong weir to the Changnyeong-Haman weir (a distance of approximately 40 km). In addition, it was predicted that the flow that included sediments in the main stream of the Nakdong River was not interrupted by the weir structure and regularly produced changes in the river bed.

• Journal of Korean Society on Water Environment
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• v.27 no.6
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• pp.855-861
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• 2011

Short-term effects of current velocity and turbid water on the benthic diatom community and water quality were examined in artificial channel ($20{\times}200{\times}10cm$) with two different experiments. The first and second experiments were consisted of different current velocities such as 1 L/min., and 1, 3, and 6 L/min., respectively. The concentration of turbid water is prepared with loess and fixed at 10 and 20 times of the turbidity of control inflow (10 NTU, LTW), respectively. At experiment 1 (EXP-1), introduction of turbid water increased dissolved oxygen, electric conductivity, pH and turbidity, but there were no differences between low- (100 NTU, MTW) and high-turbid water (200 NTU, HTW). However, experiment 2 (EXP-2) did not change any environmental parameters except dissolved total and inorganic nitrogen like EXP-1. MTW in EXP-1 strongly stimulated the growth of benthic diatom, while both MTW (150 NTU) and HTW (300 NTU) in EXP-2 did not increase or decrease the diatom abundance. Over the study, the dominant species was four, Aulacoseira ambigua, Cyclotella stelligera, Aulacoseira granulata and Achnanthes minutissima. In EXP-1, two highest species in abundance, A. ambigua and A. granulata were highly grown in MTW, while Achnanthes minutissima high in HTW adversely. These results indicate that the introduction of turbid water can play an important role in the shift of water quality and benthic diatom community in stream ecosystem, especially inflow of soil water in low current velocity.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.509-515
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• 2011

For this study the 4 sub-watersheds Okdong A, Hankang B, Jecheon A and Hankang C which are the main streams of the Han River within the mid-level region of Chungju Dam are selected and the analysis of soils has been carried out through the soil basic survey. When it comes to the soil erosion amount the soil nutrient load has been calculated by utilizing the RUSLE erosion equation. In case of the data related to the measurement of water flow and quality the information available from the "Water Information System" one of the websites run by the Ministry of Environment has been used to calculate the water pollution load. The correlation between the soil nutrient load and the water pollutant load has been analyzed through making comparison. According to the results related to the soil nutrient load of each sub-watershed the Hankang C shows the highest values TOC 29,986.92 ton/yr, TN 3,860.33 ton/yr and TP 973.97 ton/yr respectively. Even when it comes to the loads related to water quality the Hankang C shows also comparatively high values TOC 6,625.64 ton/yr, TN 7,335.01 ton/yrand TP 145.49 ton/yr respectively. The soil nutrient loads of the sub-watersheds are shown to increase towards the lower stream meaning the load increases in the order of Hankang CHankang B and Okdong A. When it comes to the water pollutant load the value goes up along down the water system meaning the load gets higher in the order of Hankang C, Hankang B and Okdong A while utilizing the mainstream within the mid-level region of Chungju Dam as the basis. The correlation study showed that the nutrient content of soil is proportional to the pollutant load in water with the strongest positive correlation with TOC.

• Journal of Korean Society on Water Environment
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• v.27 no.5
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• pp.699-709
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• 2011

The uses of multi-dimensional hydrodynamic and water quality models are increasing to support a sustainable management of large dam reservoirs in Korea. Any modeling study requires selection of a proper spatial dimension of the model based on the characteristics of spatial variability of concerned simulation variables. For example, a laterally averaged two-dimensional (2D) model, which has been widely used in many large dam reservoirs in Korea, assumes that the lateral variations of hydrodynamic and water quality variables are negligible. However, there has been limited studies to give a justification of the assumption. The objectives of this study were to present the characteristics of spatial variations of water quality variables through intensive field monitoring in Daechung Reservoir, and provide information on a proper spatial dimension for different water quality parameters. The monitoring results showed that the lateral variations of water temperature are marginal, but those of DO, pH, and conductivity could be significant depending on the hydrological conditions and local algal biomass. In particular, the phytoplankton (Chl-a) and nutrient concentrations showed a significant lateral variation at R2 (Daejeongri) during low flow periods in 2008 possibly because of slow lateral mixing of tributary inflow from So-oak Stream and wind driven patchiness.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.1
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• pp.103-116
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• 2021

Analysis of runoff is substantial for effective water management in the watershed. Runoff occurs by reaction of a watershed to the rainfall and has non-linearity and uncertainty due to the complex relation of weather and watershed factors. ANN (Artificial Neural Network), which learns from the data, is one of the machine learning technique known as a proper model to interpret non-linear data. The performance of ANN is affected by the ANN's structure, the number of hidden layer nodes, learning rate, and activation function. Especially, the activation function has a role to deliver the information entered and decides the way of making output. Therefore, It is important to apply appropriate activation functions according to the problem to solve. In this paper, ANN models were constructed to estimate runoff with different activation functions and each model was compared and evaluated. Sigmoid, Hyperbolic tangent, ReLU (Rectified Linear Unit), ELU (Exponential Linear Unit) functions were applied to the hidden layer, and Identity, ReLU, Softplus functions applied to the output layer. The statistical parameters including coefficient of determination, NSE (Nash and Sutcliffe Efficiency), NSEln (modified NSE), and PBIAS (Percent BIAS) were utilized to evaluate the ANN models. From the result, applications of Hyperbolic tangent function and ELU function to the hidden layer and Identity function to the output layer show competent performance rather than other functions which demonstrated the function selection in the ANN structure can affect the performance of ANN.