• Journal of Environmental Science International
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• v.23 no.2
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• pp.193-205
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• 2014

The direct-runoff of South Korea's representative dams (Soyanggang, Chungju, Andong, Daecheong, and Seomjingang) and precipitation were analyzed mainly with the evenly distributed spring rainfall events across the country for the last five years. For precipitation, an increasing was presented during the period 2008-2011, but did not continue to increasing 2012. The average precipitation of the five dams displayed a similar trend. Except for Chungju and Andong Dams, the trend of runoff was similar to the one shown in the precipitation. Despite the precipitation of 2009 increased, the runoff volume decreased for Andong and Chungju Dams. In addition, Chungju Dam remarkably showed a bigger runoff volume compared to other dams. As for the Sumjingang Dam, the runoff volume was the smallest, and the difference is as great as over 15-fold when compared to other runoff values. After the result of analyzing the relation between a single runoff event and synoptic weather patterns, pattern 4 contributed to the greatest impact on this event and weather patterns. The total runoff volume of the five dams for spring rain event for the last five years that exhibited this characteristic was estimated at 5.68 billion tons($10^6m^3$). Lastly, the value of this estimation was assessed as approximately 273.1 billion KRW.

• Journal of Korean Society on Water Environment
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• v.29 no.3
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• pp.309-316
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• 2013

The Non-Point Sources shows different characteristics over a wide area depending on basin situation and rainfall events etc. In addition, Among various land uses in the urban areas, runoff appears high in the paved area, though small in its size, during a heavy rain than in other land use owing to its high impervious rate, and pollutants become severly accumulated owing to continual transportation of vehicles, characteristically showing high concentrations of runoff in the early stage. As a result, several advanced countries including USA give a special emphasis on the paved area as a target for supervision. In view of these aspects, the research is not only required to consider separated sub-basins which are distributed according to land uses, but also needed to develop a suitable monitoring which is reflected rainfall-runoff relation. The on-site monitoring has been performed to collect data in object watershed as well.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.1
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• pp.53-62
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• 1982

An effort of preliminary type has been made to develope a practical method for the waterway area determination of a drainage outlet in rural or agricultural areas. The Seoul meteorological station was selected as tile index station, and the maximum rainfalls-duration-frequency (R-D-F) relation of short-time intense rainfalls was first established. A frequency analysis of the daily rainfalls for the 75 stations selected throughout the country resulted the 50-year daily rainfall for each station. The rainfall factor, which is defined here as the ration of 50-year daily rainfalls of individual station and the index station, was determined for the 8 climatological regions divided in this study. Following the US SCS method the runoff number of a watershed was given based on the soil type, land-use pattern, and the surface treatment. With this runoff number and the R-D-F relationship the runoff factors for the index station were computed and hence a nomogram could be drawn which makes it possible to determine the runoff factor for a given rainfall number and a rainfall of specific duration and frequency. With this done, the potential runoff of a watershed for a given rainfall duration could be calculated, based on the unit hydrograph theory, by multiplying the rainfall factor, the runoff factor, and the drainage area of the watershed under consideration. Then, the maximum runoff potential was determined by varying the rainfall duration and finding out the duration which results the peak discharge of a gived return period.

• Journal of Korea Water Resources Association
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• v.38 no.1
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• pp.59-71
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• 2005

Mountain watersheds are a lot of problems about soil erosion because of frequent wildfire occurrence. Runoff and soil erosion caused by the rain on a hillslope after wildfire are dependent on cover factor. And these has been a decrease by the cover factor recovery following time passage. The present paper defines the dynamic sensitivity of runoff and soil erosion that is the rate of runoff volume and soil erosion weight to rainfall energy and analyzes characteristics of the sensitivity for variation of cover factor, In according to the correlation analysis between other parameters and sensitivities, the sensitivity is the most dependent on the cover factor and the relation is exponential. The sensitivities after wildfire have suitable relation with treatment method for the mitigation of burnt forest and wildfire intensity. It was confirmed that the variation of soil erosion sensitivities come upon the range of stability in 5 years after wildfire.

• Journal of the Korean Society of Hazard Mitigation
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• v.5 no.3 s.18
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• pp.29-39
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• 2005

The objective of this study is to analyze the relation of critical duration according to hydrologic characteristics in urban areas. RRL, ILLUDAS, SWMM, and SMADA urban runoff models were applied to the Seongnae and Banpo watershed and experiment area of the Dong-Eui University. Also, hydrologic characteristics such as temporal pattern of rainfall, rainfall intensity formula, antecedent moisture condition, return period, and urban runoff model were used to simulate the critical duration of the test areas. The results of this study are as follows; (1) The type of temporal pattern of rainfall which causes maximum peak discharge in urban area has resulted in Huff's 4th quartile distribution. (2) The critical duration in urban areas were not influenced by hydrological factors except urban runoff model. (3) Peak discharge and critical duration in urban areas were influenced by the urban runoff model, and the SWMM model using Huff's 4th quartile distribution shows maximum critical duration.

• Water Engineering Research
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• v.5 no.3
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• pp.111-121
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• 2004

For the long-term strategic water resources planning, forecasting the future streamflow change is important to meet the demand of a growing society. The streamflow variation to the decade-long precipitation was investigated for the two major stage gauging stations in Korea. Precipitation and runoff characteristics have been analyzed at Yongwol stream stage in the Han River as well as Sutong stream stage in the Kum River for the future water resources management strategies. Monte Carlo method has been applied to estimate the future precipitation and runoff. Based on the trend line of 10-year moving average of runoff depth for the historical runoff records, the relation between runoff and the time variation was examined in more detail using regression analysis. This study showed that the surface flows have been significantly decreased while precipitation has been stable in these basins. Decreasing in runoff reflects the regional watershed characteristics such as forest cover changes. The findings of this study could contribute to the planning and development for the efficient water resources utilization.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.125-131
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• 2009

The aim of this study is to quantify the severity of flash food for a study watershed in Korea by estimation of flash food index using flood runoff hydrograph following Bhaskar et. al (2000). As an extension of the previous research, we examine the relation between flash food index and rainfall intensity, rainfall duration, and total runoff, respectively. This study has estimated the flash food index through simulated flood hydrographs to investigate the relative severity of flash flood in an ungauged basin, Megok river basin for 31 flood events.

• Journal of Environmental Science International
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• v.7 no.4
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• pp.415-424
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• 1998

In the rainfalll-runoff relation, consideration of the spatial movement of storms is very unportant in designing a hydraulic structure or evaluating an environmental influence for land usage. Because of thins reason, this study has suggested the finite element model which consider the spatial movement of a storm and it was applied on a small river basin(Wi stream basin). In the application of the model, the basin was treated as a pivot point and the storms are simulated 10 movement in each directions. As a result, It shows that the storms moving from north to south have higher peak discharge and faster peak time than the storms moving in other directions. So these characteristics have to be considered In the designation of a hydraulic structure or evaluation of an environmental influence.

• Journal of Korea Water Resources Association
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• v.37 no.7
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• pp.599-612
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• 2004

The continuous long-term rainfall-runoff simulation model SWAT has the advantage of being able to account for various land use, however, SWAT lacks the capability of simulating the drainage characteristics of urban area. On the other hand, SWMM, which is the most popular model for runoff analysis of urban watershed, has the advantage of being capable of considering surface and drainage characteristics in urban area, but SWMM cannot easily account for land use other than urban area within a watershed. In this study, SWAT-SWMM model, which builds on the strengths of SWAT and SWMM, has been applied to the Osan River Watershed which is a tributary watershed to the Gyung-Ahn River. From the application, the results from coupled SWAT-SWMM model has been compared to the ones from SWAT for each hydrologic component such as evapotranspiration, surface runoff, groundwater flow, and watershed and channel discharge, and the runoff characteristics of two models for each hydrologic component has been discussed.

• 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.