• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.6
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• pp.1-12
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• 2018

The objectives of this study were to develop a system linking hydrologic and water quality models considering the mechanisms of agricultural reservoir and paddy cultivation and to evaluate whether the developed system simulates hydrologic and water quality processes better than a hydrologic model that do not consider the mechanisms. The system consisted of Hydrological Simulation Program-Fortran (HSPF) as a watershed model, Module-based hydrologic Analysis System for Agricultural watersheds (MASA) as reservoir water balance model, and Chemical, Runoff and Erosion from Agricultural Management System-Paddy (CREAMS-PADDY) as a hydrologic and water quality model for paddy fields. This study carried out on the Seolseong-Cheon watershed in Icheon, and the water level and water quality had been monitored for two years at the outlet of the watershed. According to the results of this study, the performance of the simulation using HSPF-MASA-CREAMS-PADDY system was better than others, but they did not show a statistically significant difference. This seemed to be due to the uncertainty of the farming data and the water quality data of the reservoir. Therefore, if accurate input data for the system is obtained, HSPF-MASA-CREAMS-PADDY system could be used to model an agricultural watershed to obtain more realistic results. The results of this study could be utilized to the modeling of agricultural watersheds in Korea where paddy rice cultivation is dominant.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.231-243
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• 1994

A stochastic programming model for river water quality management was developed. River water quality, river flow, quality and flowrate of the wastewater treatment plant inflow were treated as random variables in the model. Withdrawal for water supply and submerged weir reaeration were included in the model itself. A probabilistic model was formulated to compute the expectation and variance of water quality using Streeter-Phelps equation. Chance constraints of the optimization problem were converted to deterministic equivalents by chance constrained method. Objective function was total annual treatment cost of all wastewater treatment plants in the region. Construction cost function and O & M cost function were derived in the form of nonlinear equations that are functions of treatment efficiency and capacity of treatment plant. The optimization problem was solved by nonlinear programming. This model was applied to the lower Han River. The results show that the reliability to meet the DO standards of the year 1996 is about 50% when the treatment level of four wastewater treatment plants in Seoul is secondary treatment, and BOD load from the tributary inflows is the same as present time. And when BOD load from Tanchon, Jungrangchon, and Anyangchon is decreased to 50%, the reliability to meet the DO standards of the year 1996 is above 60%. This results indicated that for the sake of the water quality conservation of the lower Han River, water quality of the tributaries must be improved, and at least secondary level of treatment is required in the wastewater treatment plants.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.3
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• pp.83-96
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• 2017

This study presented a surface water quality modeling framework considering the spatial resolution of pollutant load estimation to better represent stream water quality characteristics in the Saemangeum watershed which has been focused on keeping its water resources sustainable after the Saemangeum embankment construction. The watershed delineated into 804 sub-watersheds in total based on the administrative districts, which were units for pollutant load estimation and counted as 739 in the watershed, Digital Elevation Model (DEM), and agricultural structures such as drainage canal. The established model consists of 7 Mangyung (MG) sub-models, 7 Dongjin (DJ) sub-models, and 3 Reclaimed sub-models, and the sub-models were simulated in a sequence of upstream to downstream based on its connectivity. The hydrologic calibration and validation of the model were conducted from 14 flow stations for the period of 2009 and 2013 using an automatic calibration scheme. The model performance to the hydrologic stations for calibration and validation showed that the Nash-Sutcliffe coefficient (NSE) ranged from 0.66 to 0.97, PBIAS were -31.0~16.5 %, and $R^2$ were from 0.75 to 0.98, respectively in a monthly time step and therefore, the model showed its hydrological applicability to the watershed. The water quality calibration and validation were conducted based on the 29 stations with the water quality constituents of DO, BOD, TN, and TP during the same period with the flow. The water quality model were manually calibrated, and generally showed an applicability by resulting reasonable variability and seasonality, although some exceptional simulation results were identified in some upstream stations under low-flow conditions. The spatial subdivision in the model framework were compared with previous studies to assess the consideration of administrative boundaries for watershed delineation, and this study outperformed in flow, but showed a similar level of model performance in water quality. The framework presented here can be applicable in a regional scale watershed as well as in a need of fine-resolution simulation.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.6
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• pp.11-20
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• 2007

In order to make the way to determine the instream flow more practically, we have investigated many case studies and reviewed reports and papers. To validate instream flow level suggested by the case studies, DAWAST and HEC-RAS model were applied to the Gap-stream watershed in Daejeon city. Flow-duration analysis was performed both with the stream flow data gauged in the Indong, Boksu, and Hoeduck stations, and with the stream flow data estimated by the DAWAST model and the specific discharge method. Instream flow was determined among the flow-duration analysis, DAWAST, HEC-RAS model and mass balance approach. It was satisfied with various factors such as target water quality, water depth for eco-system and resorts, water surface width, flow velocity for landscape in dry season. The study suggested that the mean low flow could be replaced into the instream flow for the preliminary study because the instream flow considering ecosystem, landscape, water-friendly environment and water quality was generally close to the mean low flow.

• Journal of Environmental Impact Assessment
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• v.21 no.3
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• pp.445-460
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• 2012

In order to evaluate and predict the environmental impact of the low-trophic-level ecosystem to environmental changes in the Yellow Sea and the East China Sea, an ecological modelling study was undertaken. Simulation results of average distribution patterns and concentrations of water quality factors during the summer by the model were acceptable. Phytoplankton and remineralization rate of organic matter were very important parameters by a sensitivity analysis. Water quality factors showed high values in the estuary of the Yangtze River and in the West and South Sea of Korea and low values in the central area of the Yellow Sea. There is a plume of high values, especially nutrients, off the mouth of the Yangtze that expands or contracts with changes in the discharge strength. Characteristics of responses of water quality factors vary for different scenarios of environmental change, such as land-based pollution sources and atmospheric forcing. It is suggested that changes of light intensity, discharges of input sources, and wind play an important role in the marine ecosystem.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1999.10c
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• pp.783-788
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• 1999

In this study, a decision support system (DSS) was developed to calculate optimal wastetreatment cost, treatment level and treatment quantity of various pollutants for applying for in rural basin. The DSS includes a gegraphic informatino system (GIS), relational database system (RDBS), water quality models(Loading function , WASP5), watershed pollution load calculation module(SPLC), optimal water quality management plan to satisfy the water quality regulations. The system can be modified by user to trace the optimal condition for decision. The effort was conducted to apply the developed DSS to select the for optimal water quality management plan small rural basin called Kwanri Stream.

• Journal of Korean Society of Rural Planning
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• v.8 no.1 s.15
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• pp.60-68
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• 2002

A Modified CREAMS model, CREAMS-PADDY was developed to simulate the hydrology and nutrient transport at an irrigated rice paddy. The hydrology at a paddy was simulated by a daily water balance routine which reflects daily inflow, outflow, and water level changes. The soil erosion was simulated using modified USLE. The nutrient transport for total nitrogen and phosphorus were depicted for various phases of each constitute such as extraction, percolation, mineralization, and plant uptakes. Field monitoring was conducted to investigate the water quality changes at a paddy field at three times a week during the growing season of 1996. The proposed model simulates the water quality of the paddy reasonably well, and is found to be applicable to field conditions.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.536-542
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• 2000

The purpose of this study is to evaluate the effect of stream quality by the farmer＇s livestock wastes management in a typical small agricultural watershed. AGNPS model has the capability to adjust the level of pollutant load from farmstead and the fertilization level of upland field. A small agricultural watershed(4.12 $\textrm{km}^2$) which has as livestock farmhouses located in Gosan-myun, Ansung-gun was selected. AGNPS data were prepared by using Arc/info and Idrisi. 4 storm events in 1999 was used for runoff calibration, and 2 storm event which is measured in hourly-base at 4 locations along the stream were used for water quality(TN, TP) calibration. Model＇s behavior to stream quality for 3 cases was investigated. First, the variation of pollution produced from the cattle shed affected little to the stream quality because the cattle sheds were roofed. Second, the good management of ground in farmstead affected to stream quality with 11% and 17% decrease in TN and TP, respectively. Third, the reduction of fertilization level to upland field affected to stream quality with 27.2% and 38.5% decrease in TN and TP, respectively.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.2
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• pp.91-98
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• 2009

The long-term water-quality change of Asan Bay by the influx of polluted disposal water was predicted through a simulation with an Eco-hydrodynamic model. Eco-hydrodynamic model is composed of a multi-level hydrodynamic model to simulate the water flow and an ecosystem model to simulate water quality. The water quality simulation revealed that the COD(Chemical Oxygen Demand), dissolved inorganic nitrogen(DIN) and dissolved inorganic phosphorus(DIP) are increased at 5 stations for the subsequent 6 months after the influx of the effluent. COD, DIN and DIP showed gradual decreases in concentration during the period of one to two years after the increase of last 6 months and reached steady state for next three to ten years. Concentration levels of COD, DIN, and DIP showed the increase by the ranges of $11{\sim}67%$, $10{\sim}67%$, and $0.5{\sim}7%$, respectively, which represents that the COD and DIN are the most prevalent pollutants among substances in the effluent through the sewage treatment plant. The current water quality of Asan Bay based on the observed COD, TN and TP concentrations ranks into the class II of the Korean standards for marine water quality but the water quality would deteriorate into class III in case that the disposal water by the sewage plant is discharged into the Bay.

• Journal of Ocean Engineering and Technology
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• v.20 no.1 s.68
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• pp.55-62
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• 2006

Recently, pollution by development in coastal areas is going from bad to worse. The Korean government is attempting to make policies that prevent water pollution, but it is still difficult to say whether such measures are lowering pollution to an acceptable level. More specifically, the general investigation that has been done in KOREA does not accurately reflect the actual conditions of pollution in coastal areas. An investigation that quantitatively assesses water quality management using rational prediction technology must be attempted, and the ecosystem model, which incorporates both the 3-dimensional hydrodynamic and material cycle models, is the only one with a broad enough scope to obtain accurate results. The hydrodynamic model, which includes advection and diffusion, accounts for the ever-changing flow and (quality) of water in coastal areas, while the material cycle model accounts for pollutants and components of decomposition as sources of the carbon, phosphorus, and nitrogen cycles. In this paper, we simulated the rates of dissolved oxygen (DO), chemical oxygen demand (COD), total nitrogen(T-N) and total-phosphorous(T-P) in Korea's Ulsan Area. Using the ecosystem model, we did simulations using a specific set of parameters and did comparative analysis to determine those most appropriate for the actual environmental characteristics of Ulsan Area. The simulation was successful, making it now possible to predict the likelihood of coastal construction projects causing ecological damage, such as eutrophication and red tide. Our model can also be used in the environmental impact assessment (EIA) of future development projects in the ocean.