• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.531-537
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• 2017

The biologic Oxygen Demand (BOD) is a reliable and generally accepted indicator of water pollution by organic pollutants. Accordingly, estimation of BOD export from paddies carries important implications fwith regard to water management in rural areas. In this study, hydrology and BOD concentration were monitored during the period 2008 through 2012, in an effort to understand the characteristics of BOD export from paddy fields. The findings demonstrated that BOD load by rainfall above 50 mm. occupied about 50 % of total load, whereas the load by less than ten mm. rainfall occupied about 29 % of the total load during periods of stormy activity. It therefore seems that it could be possible to reduce the BOD load up to 29 % during storm periods, when drainage control conducted for rainfall less than ten mm.(an amount which is relatively easy to manage). The documented mean loads of storm and non-storm were $17.1kg\;ha^{-1}\;yr^{-1}$ and $11.2kg\;ha^{-1}\;yr^{-1}$, respectively. The BOD load during the significant rainfall period was similar to the renewed unit load by NIER (2014). However, there were substantial differences between unit load and actual load when the non-storm load was incorporated into the BOD load estimation from paddy fields. In view of the foregoing, it is felt that, the non-storm load needs to be further considered and managed for the successful implementation of Total Maximum Daily Load (TMDL) program.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.3
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• pp.15-22
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• 2019

In order to preserve water environment, Total Maximum Daily Load(TMDL) is used to manage the total amount of pollutant from various sources, and the annual average load of source is calculated by the unit load method. Determination of the unit load requires reliable data accumulation and analysis based on a reasonable estimation method. In this study, we propose a revised unit load estimation method by analyzing the unit load calculation procedure of National Institute of Environment Research(NIER) method. Both methods were tested using observed runoff ratio and water quality data of rice paddy fields. The estimated values with the respective NIER and revised NIER methods were highly correlated each other. However, the Event Mean Concentration(EMC) and the runoff ratio considered in the NIER method appeared to be influenced by rainfall classes, and the difference in unit load increases as the runoff and EMC increase. The error can be further increased when the EMC and runoff ratio are changed according to changes in rainfall patterns by climate change and change of agricultural activities. Therefore, it is recommended to calculate unit load by applying the revised NIER method reflecting the non point pollution runoff characteristics for different rainfall classes.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.1
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• pp.121-130
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• 2019

The purpose of this study is to determine the amount of irrigation water for upland crop growth based on the 30 year of historical rainfall data and the water management guidelines as a reference. Five regions and ten crops were selected by their cultivation size. The changes of soil moisture contents were calculated using daily mean rainfall and irrigation demand. This study assumed that crops are irrigated when the soil moisture contents fell below of the field capacity for more than 5 days, which is the drought condition defined by RDA. The maximum irrigation water requirements was 167.2 mm for chinese cabbage during the growing season, which was followed by corn (112.0 mm), daikon (102.3 mm), spinach (66.1 mm), lettuce (56.7 mm), pepper (46.5 mm), potato (33.9 mm), sweet tomato (27.4 mm), peanut (11.5 mm) and bean (10.3 mm), The results of this study could contribute to providing valuable data to determine the capacity of irrigation facilities and to establish the emergency operation plans under extreme unfavorable weather condition (heat wave, etc.) for crop growth.

• Journal of Korea Water Resources Association
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• v.54 no.6
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• pp.381-393
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• 2021

As part of the National Disaster Management Research Institute's Official Development Assistance (ODA) projects for transferring new technologies in the field of disaster-safety management, a flood forecasting and warning system was established in 2019 targeting the Borikhan in the Namxan River Basin in Bolikhamxai Province, Laos. In the target area, which is an ungauged small and medium river basin, observation stations for real-time monitoring of rainfall and runoff and alarm stations were installed, and a software that performs real-time data management and flood forecasting and warning functions was also developed. In order to establish a flood warning standard and develop a nomograph for flood prediction, hydraulic and hydrological analysis was performed based on the 30-year annual maximum daily rainfall data and river morphology survey results in the target area. This paper introduces the process and methodology used in this study, and presents the results of the system's applicability review based on the data observed and collected in 2020 after system installation.

• Journal of Korean Society on Water Environment
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• v.35 no.6
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• pp.497-509
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• 2019

After the Total Maximum Daily Loads(TMDLs) was applied, it became beyond the limit of concentration management. However, it does not adequately reflect the characteristics of various watersheds, and causes problems with local governments because of the standard flow set. Thus, in this study, the Han River system is organized into four groups in estimating the Pollution Contribution by applying the Flow Duration Curve(FDC) created by the daily flow of data from the HSPF. And the method of this study is expected to be valuable as basic data for the TMDLs. As a result, Group I contains the main watersheds with no large hydraulic structures and tributary watersheds. There is no specificity in the FDC and the Pollution Contribution is estimated as rainfall runoff. Group II contains watersheds near the city where the FDC is maintained above a certain level during the Low Flow Conditions and the Pollution Contribution is estimated as the discharge flow of large scale point pollution facilities. Group III contains the main watersheds in which the large hydraulic structures are installed and FDC is curved in the Low Flow Conditions. So the Pollution Contribution is estimated as the water quality of the large hydraulic structures. Group IV contains the upstream in mainstream watersheds in which the large hydraulic structures are installed and the FDC is disabled before the Low Flow Conditions. As the flow is concentrated in the High Flow Conditions, the non-point pollution sources are estimated as the Pollution Contribution.

• Journal of the Korean Geographical Society
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• v.39 no.5 s.104
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• pp.711-721
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• 2004

The aim of this study is to clarify whether frequency and/or severity of extreme climate events have changed significantly in Korea during recent years. Using the best available daily data, spatial and temporal aspects of ten climate change indicators are investigated on an annual and seasonal basis for the periods of 1954-1999. A systematic increase in the $90^{th}$ percentile of daily minimum temperatures at most of the analyzed areas has been observed. This increase is accompanied by a similar reduction in the number of frost days and a significant lengthening of the thermal growing season. Although the intra-annual extreme temperature range is based on only two observations, it provides a very robust and significant measure of declining extreme temperature variability. The five precipitation-related indicators show no distinct changing patterns for spatial and temporal distribution except for the regional series of maximum consecutive dry days. Interestingly, the regional series of consecutive dry days have increased significantly while the daily rainfall intensity index and the fraction of annual total precipitation due to events exceeding the $95^{th}$ percentile for 1901-1990 normals have insignificantly increased.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.35-43
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• 1999

The purpose of this study is to derive the optimal methodology estimating the changes of fluvial hydraulic characteristics due to semi-covering work of urban stream. First, after collecting the data of the daily maximum rainfall of Chungju gaging station, the frequency analysis was carried out with frequency factor method, which includes normal, two-parameter and three-parameter lognormal, Gumbel-Chow, pearson type III, log-pearson type III distribution, and the goodness of fit test was executed by $x^2$-test and Kormogorov-Smimov test. Using the SCS method, the effective rainfall was estimated and the peak flow was calculated by the area-routing method. The HEC-2 model was applied to calculate water surface profiles for steady, gradually varied flow at Kyohyun river system in Chungju city. The model was applied to floodplain and riverbed management to evaluate flood way encroachments and to delineate flood hazard by riverside roadway construction. The model also was used to evaluate effects on water surface profiles of river improvement and levees as well as the presence of bridges or other hydraulic structures in the floodplain.

• Journal of Korean Society on Water Environment
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• v.21 no.4
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• pp.385-392
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• 2005

The control of nonpoint source pollution is essentially needed to successfully perform the Total Maximum Daily Load program. Of the various land uses in the nonpoint source, the paved areas such as a parking lot and a bridge are stormwater intensive land uses because of high imperviousness and high pollutant mass emissions. This research was performed to understand the magnitude and nature of the stormwater emissions with the purposes of quantifying stormwater pollutant concentrations and mass emission rates from a parking lot and a bridge. Two monitoring sites in Kongju city were equipped with an automatic rainfall gages and an automatic flow meter for accumulating the data such as rainfall, water quality and runoff flow rates. This paper will summarize the metal concentration changes during the storm duration and metal EMCs to characterize the concentration profiles in a parking lot and a bridge. Also a new concept, dynamic EMC, will be proposed to find the relationship between EMC and first flush effect. It can be used to determine the economical treatment criteria in best management practices.

• Journal of Wetlands Research
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• v.11 no.2
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• pp.67-76
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• 2009

The contribution of pollutant loadings from non-point source (NPS) to the four major rivers in Korea exceeded 22~37 % of the total loadings in 2004 and is expected to reach 60 % in 2020. Most of NPS loadings are coming from urban areas, especially from paved areas. Because of high imperviousness rate, many types of NPS pollutant are accumulating on the surface during dry periods. The accumulated pollutants are wash-off during a storm and highly degrading the water quality of receiving water bodies. For this reason, the Korean Ministry of Environment (MOE) developed the Total Maximum Daily Load (TMDL) program to protect the water quality by managing the point source and NPS loadings. NPS has high uncertainties during a storm because of the characteristics of rainfall and watershed areas. The rainfall characteristics can affect on event mean concentrations (EMCs), mass loadings, flow rate, etc. Therefore, this research was performed to determine EMCs for rainfall ranges from transportation landuses such as road and parking lot. Two sites were monitored over 45 storm events during the 2006/06 through 2008/10 storm seasons. Mean TSS EMCs decrease as rainfall ranges increase and highest at less than 10mm rainfall. The results of this study can be used to determine the efficient scale of BMP facility considering specific rainfall range.

• Journal of Korea Water Resources Association
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• v.32 no.3
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• pp.265-279
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• 1999

In this study, one of the techniques on the extension of low flow series has been developed, in which the daily streamflows were simulated by the Tank model with the input of extended daily rainfall series which were stochastically generated by the Markov chain model. The annual lowest flow serried for each of the given durations were formulated form the simulated daily streamflow sequences. The frequency of the estimated annual lowest flow series was analyzed. The distribution types to be used for the frequency analysis were two-parameter and three-parameter log-normal distribution, two-parameter and three-parameter Gamma distribution, three-parameter log-Gamma distribution, Gumbel distribution, and Weibull distribution, of which parameters were estimated by the moment method and the maximum likelihood method. The goodness-of-fit test for probability distribution is evaluated by the Kolmogorov-Sminrov test. The fitted distribution function for each duration series is applied to frequency analysis for developing duration-low flow-frequency curves at Yongdam Dam station. It was shown that the purposed technique in this study is available to generate the daily streamflow series with fair accuracy and useful to determine the probabilistic low flow in the watersheds having the poor historic records of low flow series.