• Journal of Korean Society of Environmental Engineers
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• v.38 no.3
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• pp.117-127
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• 2016

In this study, analyzed scenarios of the environmental instream flow for water quality improvement in Saemangeum watershed. In order to get an environmental instream flow, Methodology is selected for Retention-Basin, reservoir expansion, new dam construction, Modification of water intake and drainage system, Rearrangement of plan for system which Yongdam and Seomjin river dam have been used water supply. The study composed of diverse scenario of Environmental instream flow increasement and analyzed the effect of improving the water quality by the QUAL2K model and calculation of runoff for saemangeum watershed by SWAT model. The following water quality indicators have been simulated in irrigation and non-irrigation period for BOD and T-P. When scenarios applied to water quality model, Improvement rate in the water quality for Total Maximum Daily loads of Mankyung B unit watershed during irrigation and non-irrigation period is BOD (28.70%), T-P (17.09%) and BOD (28.51%), T-P (28.68%) respectively. Dongjin A unit watershed during irrigation and non-irrigation period is BOD (14.39%), T-P (14.59%) and BOD (15.54%), T-P (19.46%) similary. Simulation results is to quantify the constribution of the improvement in the water quality. In particular, It was demonstrative that improving effect for water quality was evaluated to be great in non-irrigation period.

• Magazine of the Korean Society of Agricultural Engineers
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• v.15 no.4
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• pp.3170-3180
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• 1973

This study of the subject will review past and present irrigation development in Korea. Particular attention will be given to water pricing structure and a case study on the purpose of rational operation and management of irrigation water and organizations, and the optimum irrigation water and organizations, and the optimum irrigation water fee inorder to reduce farmers burden and to rationalize the farmland associations management so as to achieve development of the rural environment. In 1971, the reservoir of the Farmland Improvement A sociation (FIA) produced only 775 millison $m^3$ of irrigation water or 77% of planned capacity of 1,015 million $m^3$. It was caused by inefficient maintenance of irrigation facilities; for instance, about 21% of reservoirs, pumping stations and weirs in Korea have been silted by soil erosion which hinder to water production according to an ADC survey. The first Irritation Association was established in 1906, whcih was renamed the Farmland Assoeiation by the Rural Development Enouragement Law in 1970. By the end of 1971, 411,000 ha of rice paddies were under the control of 267 associations nationwide. The average water price assessed by Associations nationwide rose from 790 won per 0.1 ha. in 1966 to 1,886 won in 1971. The annual growth rate was 20%. The highest water price in 1971 was 4,773 won her 0.1 ha. and the lowest was 437 won. This range was caused by differences in debt burden, geographic conditions and management efficiency among the Associations. In 1971, the number of Associations which exceeded the average water price of 1,886 won per 0.1 ha. was 144, or 55.1% of all Association. In determination of water price, there are two principles; one is determined by production cost such as installation cost of irrigation facilities, maintenance cost, management cost and depreciation ect. For instance, the Yong San River Development project was required 33.7 billion won for total construction and maintenance cost is 3.1 billion won for repayment, maintenance and management cost per year. The project produces 590 million $m^3$ of irrigation water annually. Accordingly, the water price per $m^3$ is 5.25 won. The other principle is determined by water value in the crop products and in compared with production of irrigated paddy and non-irrigated paddy. By using this method, water value in compared with paddy rice vs. upland rice(Average of 1967-1971) was 14.15 won per $m^3$ and irrigated paddy vs. non-irrigated paddy was 2.98 won per $m^3$. In contrast the irrigation fee in average association of 1967-1971 was 1.54 won per $m^3$. Accordingly, the current national average irrigation fee(water price) is resonable compared with its water value. In this study, it is found that the ceiling of water price in terms of water value is 2.98 won per $m^3$ or 2,530 won per 0.1 ha. However, in 1971 55% of the associations were above the average of nationwide irrigation fees. which shows the need for rationalization of the Association's management. In connection with rationalization of the Association's management, this study recommends the following matters. (1) Irrigation fee must be assessed according to the amount of water consumption taking intoaccount the farmer's ability. (2) Irrigation fee should be graded according to behefits and crop patterns. (3) Training personnel in the operation and procedures of water management to save O&M costs. (4) Insolvent farmland association should be integrated into larger, sound associations in the same GUN in order to reduce farmers' water cost. (5) The maintenance and repair of existing irrigation facilities is as important as expansion of facilities. (6) Establishment of a new Union of Farmland Association is required to promoted proper maintenance and to protect the huge investment in irrigation facilities by means of technical supervision and guidance.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.5
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• pp.115-124
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• 2018

Resilience has been widely used in various fields including design and operation of infrastructures. The resilient infrastructures not only reduce the damage scale of various disasters but also reduce the time and cost required for restoration. However, resilience rarely applied to promote efficient management of agricultural infrastructures. Recently, drought is an aggravating disaster by climate change and need countermeasures. Therefore, we tried to demonstrate evaluating measures in case of drought under consideration of resilience. This study applied the robustness-cost index (RCI) to evaluate alternative solution of the supply problem of a large agricultural reservoir under drought conditions. Four structural alternatives were selected to estimate the robustness index (RI) and the cost index (CI) to obtain the RCI values. Structural alternatives are classified into temporary measures and permanent measures. Temporary measures include the development of a tube wells and the installation of the portable pump, while the permanent measures include the installation of a pumping stations and the pumping water to the reservoir (Yeongsan River-Naju reservoir). RCI values were higher in permanent measures than those of temporary measures. Initial storage of the reservoir also affected RCI values of the drought measures. Permanent measures installation and management of early stage of the reservoir storage shortage was identified as the most resilient system.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.673-678
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• 2005

The objective of this paper is to develop the microorganism concentration simulation model for the health related effect analysis while farmers and water managers reuse the wastewater for agricultural irrigation. This model consists of the CE-QUAL-R1 model and the CREAMS-PADDY model. The CE-QUAL-R1 model is the 1-D numerical model to analyze the water quality of the reservoir and the CREAMS-PADDY model is modified from CREAMS model for considering the hydrologic cycles in paddy field. This model was applied to examine the application by the observed data from 2003 in Byoungjum study area. From this research, the average root mean square error (RMSE) for the simulated concentration during the calibration period was 0.51 MPN/100ml and correlation coefficient $(R^2)$ was 0.71. And the RMSE for the simulated concentration during the verification period was 0.46 MPN/100ml and $R^2$ was 0.73. This simulation results show that the coliform inflow concentrations by the wastewater irrigation wield great influence upon the temporal coliform concentrations in paddy field.

• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.1
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• pp.63-72
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• 1994

The objective of the study is to develop weather generators for daily rainfall and small pan evaporation and to test the applicability with recorded data. Daily rainfall forecasting model(DRFM) was developed that uses a first order Markov chain to describe rainfall seque- nces and applies an incomplete Gamma function to predict the amount of precipitation. Daily evaporation forecasting model(DEFM) that adopts a normal distribution function to generate the evaporation for dry and wet days was also formulated. DRFM and DEFM were tested with twenty year weather data from eleven stations using Chi-square and Kolmogorov and Smirnov goodness of fit tests. The test results showed that the generated sequences of rainfall occurrence, amount of rainfall, and pan evaporation were statistically fit to recorded data from eleven, seven, and seven stations at the 5% level of significance. Generated rainfall data from DRFM were very close in frequency distri- bution patterns to records for stations all over the country. Pan evaporation for rainy days generated were less accurate than that for dry days. And the proposed models may be used as tools to provide many mathematical models with long-term daily rainfall and small pan evaporation data. An example is an irrigation scheduling model, which will be further detailed in the paper.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.17-24
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• 2012

The main purposes of the agricultural reservoir enlargement (ARE) project are to secure water supply reliability (WSR) for agriculture and to release environmental water during dry seasons. In this study, an operational rule that will simultaneously satisfy both the above issues was developed. Initial amount of water storage at the beginning of non-irrigation season (1st October) was divided into 3 stages, and the target level of water storage at the beginning of irrigation seasons (1st April) was set up. Required operational curves and release amounts were estimated based on the stages and target water levels. To evaluate the applicability of this rule, the amount of water released for environmental purposes and WSRs were analyzed for three reservoirs (Unam, Jangchi and Topjeong). The ratio between annual amount of release and additional amount of water storage were 1.6, 1.85, and 4.1 for the Unam, Jangchi, Tapjeong reservoirs, respectively. Also, the WSRs of all reservoirs were found to become higher than when the design standard was applied. Therefore, it is considered that the proposed rule is more suitable for the enlarged agricultural reservoirs operation as it satisfies the WSRs while securing the environmental water release.

• Journal of Korean Society on Water Environment
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• v.35 no.2
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• pp.131-144
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• 2019

Climate Change affects the hydrological cycle in agricultural watersheds through rising air temperature and changing rainfall patterns. Agricultural watersheds in Korea are characterized by extensive paddy fields and intensive water use, a resource that is under stress from the changing climate. This study analyzed the effects of climate change on river flows for Geum Cheon and Eun-San Choen watershed using STREAM, a semi-distributed watershed model. In order to evaluate the performance and improve the reliability of the model, calibration and validation of the model was done for one flow observation point and three reservoir water storage ratio points. Climate change scenarios were based on RCP data provided by the Korea Meteorological Administration (KMA) and bias corrections were done using the Quantile Mapping method to minimize the uncertainties in the results produced by the climate model to the local scale. Because of water mass-balance, evapotranspiration tended to increase steadily with an increase in air temperature, while the increase in RCP 8.5 scenario resulted in higher RCP 4.5 scenario. The increase in evapotranspiration led to a decrease in the river flow, particularly the decrease in the surface runoff. In the paddy agricultural watershed, irrigation water demand is expected to increase despite an increase in rainfall owing to the high evapotranspiration rates occasioned by climate change.

• KCID journal
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• v.21 no.1
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• pp.55-63
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• 2014

A sedimentation basin for agricultural water quality improvement was researched to analyze the water quality purification characteristics. The sedimentation basin constructed at the inlet of Gamdon reservoir in Muan-gun, Jeollanam-do was selected as the research field of this study. The surface area of the sedimentation basin is $34,000m^2$, volume is $122,000m^3$, and hydraulic retention time is 0.3hr~7.3day. The average influent loading of SS was 156.6kg-SS/d, and the effluent loading was 67.5kg-SS/d with the average removal rate of 56.9%. The average influent loadings of BOD and COD were 33.0kg-BOD/d and 60.3kg-COD/d respectively, and the effluent loadings were 26.4kg-BOD/d and 48.6kg-COD/d with the average removal rate of 20.1% and 19.3% respectively. Therefore, the results of this study show that a sedimentation basin can purify SS and organic matters. The average influent loadings of T-N and T-P were 28.7kg-TN/d and 2.97kg-TP/d respectively, and the effluent loadings were 16.3kg-TN/d and 1.41kg-TP/d with the average removal rate of 43.0% and 52.6% respectively. In conclusion, the overall results of this study show that a sedimentation basin is a feasible alternative to purify organic matters and nutrients.

• Earthquakes and Structures
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• v.18 no.3
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• pp.285-296
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• 2020

Dams are important structures for management of water supply for irrigation or drinking, flood control, and electricity generation. In seismic regions, the structural safety of concrete gravity dams is important due to the high potential of life and economic loss if they fail. Therefore, the seismic analysis of existing dams in seismically active regions is crucial for predicting responses of dams to ground motions. In this paper, earthquake response of concrete gravity dams is investigated using the finite element (FE) method. The FE model accounts for dam-water-foundation rock interaction by considering compressible water, flexible foundation effects, and absorptive reservoir bottom materials. Several uncertainties regarding structural attributes of the dam and external actions are considered to obtain the fragility curves of the dam-water-foundation rock system. The structural uncertainties are sampled using the Latin Hypercube Sampling method. The Pine Flat Dam in the Central Valley of Fresno County, California, is selected to demonstrate the methodology for several limit states. The fragility curves for base sliding, and excessive deformation limit states are obtained by performing non-linear time history analyses. Tensile cracking including the complex state of stress that occurs in dams was also considered. Normal, Log-Normal and Weibull distribution types are considered as possible fits for fragility curves. It was found that the effect of the minimum principal stress on tensile strength is insignificant. It is also found that the probability of failure of tensile cracking is higher than that for base sliding of the dam. Furthermore, the loss of reservoir control is unlikely for a moderate earthquake.

• Korean Journal of Ecology and Environment
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• v.38 no.spc
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• pp.39-43
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• 2005

The dynamics of water quality with the storm events were analyzed in a small reservoir for irrigation, Lake Wangkung. Water quality of the inflowing stream fluctuated seasonally with the variation of flow rate. Thermal stratification was consistent from April to October below 2 m depths and anoxic layer was developed below 2 m depth in summer. The unique feature of temperature showed that thermal stratification was disrupted by a heavy rain event during monsoon, but hypolimnetic hypoxia were reestablished after a few days. Phosphorus and nitrogen increased immediately following storm events. The marked increase may be due to the input of P-rich storm runoff from the watershed. Internal phosphorus loading can be one of the explanations for TP increases in summer. When there was a storm, total populations of phytoplankton and zooplankton was reduced immediately following the storm, indicating possible flushing of algae and zooplankton. After a lag period of low-density the plankton population bloomed to a peak again within five days after the storm. Turbid water in lake became clear again which coincided with the time of the phytoplankton buildup. The results demonstrate that water quality is regulated greatly by rainfall intensity in Lake Wangkung.