• Journal of Industrial Technology
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• v.3
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• pp.69-74
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• 1983

For the determination of a reservoir capacity Rippl's mass-curve method has long been used with the past river flow data assuming the same flow records will be repeated in the future. This study aims to find out a better method for determining the reservoir capacity by employing the analytical theory based on the stochastic process. For the present study the synthetic generation methods of Thomas-Fiering type was used to synthetically generate 50 years of monthly river inflows to three single-purpose reservoirs and three multi-purpose reservoirs. The generated sequences of monthly flows were analyzed based on the range concept. With the optimum operation rule of the reservoirs as the one which maximizes the water-use downstream the waterrelease from the reservoir was determined and with due consideration to the mean inflows and the range of monthly flows the required reservoirs capacity was stochastically determined. It was possible to repersent the so-determined reservoir capacity in terms of the mean monthly inflows and the number of subseries in the determination of ranges. It is suggested that the result obtained in this study would be applied to approximately estimate, in the stage of preliminary design, the required capacity of a reservoir in question with the limited information such as the mean monthly inflow and the period of reservoir operation.

• KCID journal
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• v.17 no.2
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• pp.95-104
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• 2010

Water quality data for 10 years (2000~2009) from about 826 reservoirs that are operated as a agricultural water quality survey network were analyzed in order to seek water quality management plan based on physical and chemical characteristics of agricultural reservoirs. The 95% reservoirs that exceed agricultural water quality standard of Chl-a (35mg/ $m^3$) had effective water depth shallower than 5m. The reason was that the reservoirs had more inflows of nutrient salts from the watershed, bigger surface water area of weak structure to algae occurrence. As the reservoirs of effective water depth shallower than 5m cover 49% of benefited area for irrigation, it is critical for agricultural water quality management of the reservoirs. The water quality of reservoir with shallower than 5m effective water depth was worse than reservoir with deeper than 5m effective water depth. Therefore, it is desirable that effective water depth of reservoirs make more than 5m for water quality management by building the bank higher and dredging the bottom of reservoirs.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.5
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• pp.1-12
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• 2015

The study aimed to project inflows and demmands for the agricultural reservoir watersheds in South Korea considering a variety of regional characteristics and the uncertainty of future climate information. The study bias-corrected and spatially downscaled retrospective daily Global Climate Model (GCM) outputs under Representative Concentration Pathways (RCP) 4.5 and 8.5 emission scenarios using non-parametric quantile mapping method to force Soil and Water Assessment Tool (SWAT) model. Using the historical simulation, the skills of un-calibrated SWAT model (without calibration process) was evaluated for 5 reservoir watersheds (selected as well-monitored representatives). The study then, evaluated the performance of 9 GCMs in reproducing historical upstream inflow and irrigation demand at the five representative reservoirs. Finally future inflows and demands for 58 watersheds were projected using 9 GCMs projections under the two RCP scenarios. We demonstrated that (1) un-calibrated SWAT model is likely applicable to agricultural watershed, (2) the uncertainty of future climate information from different GCMs is significant, (3) multi-model ensemble (MME) shows comparatively resonable skills in reproducing water balances over the study area. The results of projection under the RCP 4.5 and RCP 8.5 scenario generally showed the increase of inflow by 9.4% and 10.8% and demand by 1.4% and 1.7%, respectively. More importantly, the results for different seasons and reservoirs varied considerably in the impacts of climate change.

• Water for future
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• v.19 no.2
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• pp.149-156
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• 1986

The generated sequences of monthly flows were analyzed based on the range concept. With the optimum operation rule of the reservoirs as the one which maximizes the wateruse downstream the waterrelease from the reservoir was determined and with \ulcorner consideration to the mean inflows and the range of monthly flows the required reservoirs capacity was stochastically determind. It is suggested that the result obtained in this study would be applied to approximately estimate, in the stage of preliminary design, the required capacity of a reservoir in question with the limited information such as the mean monthly inflow and the period of reservoir operation. For the determination of a reservoir capacity Rippl's mass-curve method has been long used with the past river flow data assuming the same flow records will be repeated in the future. This study aims to find out a better method for determining the reservoir capacity by employing the analytical theory based on the stochastic process. For the present study the synthetic generation methods of Thomas-Fiering type was used to synthetically generate 50 years of monthly river inflows to three single-purpose reservoirs and three multi-purpose reservoirs.

• Magazine of the Korean Society of Agricultural Engineers
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• v.33 no.4
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• pp.52-60
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• 1991

This study was conducted to investigate the appropriate operation method minimizing the deviation between irrigation water demand and release from the reservoirs, and the simulation technique was used in the operation model. This model was applied to the grouped reservoirs system consisted of Dongsang, Daia and Keungchun reservoirs and Eowoo-weir in Chonbuk FLIA district. The results obtained in this study are summarized as follows; 1.The area above the Eowoo weir point was divided into 6 small watersheds, and daily inflows from each watershed were calculated by Tank model. It showed that the average annual runoff ratio was 40-60% respectively. 2.Based on the Blaney-Criddle formula daily water requirement of Chonbuk FLIA irrigation area was estimated, mean water requirement for paddy field during the irrigation period was 818.lmm. 3.Using the basic data such as inflow and water demand, four different release types were selected. Through the simulated operation the difference between intake water required at Eowoo-weir point and release from the 3 reservoirs was estimated. The best result was obtained when Daia and Keungchun reservoirs are operated parallelly at fixed release ratio and the release of Dongsang reservoir was determined according to the storage of Daia reservoir.

• Journal of Wetlands Research
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• v.3 no.1
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• pp.49-59
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• 2001

The objective of this study is to provide the results of frequency analysis for Dong-eup reservoir, in which the environmental and ecological roles in addition to the water supply and flood control capacity of the reservoir are increased rapidly. The suggested results are the frequency analysis of annual maximum rainfall data based on eight different rainfall duration data at Masan and Milyang raingauge stations. We also provide the probabilistic inflows from subbasins and evaluate the stage increases of the reservoir. As results, the 24-hour and 100-year return period rainfall is 291.8 mm and consequently inflows are 361.79 cms for Junam, 192.57 for Sannam and 408.28 for Dongpan reservoirs. The 24-hour and 100-year return period reservoir stages are expected as 5.08 m, 5.51 m and 6.89 m depending on the initial reservoir stage. The suggested results of frequency analysis of rainfalls, inflows and reservoir stages in this study will be useful for the scientific and systematic management of the reservoir.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.516-516
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• 2022

Agricultural reservoirs are critical water resources structures to ensure continuous water supplies for rice cultivation in Korea. Climate change has increased the risk of reservoir failure by exacerbating discrepancies in upstream runoff generation, downstream irrigation water demands, and evaporation losses. In this study, the variations in water balance components of 400 major reservoirs during 1973-2017 were examined to identify the reservoirs with reliable storage capacities and resilience. A conceptual lumped hydrological model was used to transform the incident rainfall into the inflows entering the reservoirs and the paddy water balance model was used to estimate the irrigation water demand. Historical climate data analysis showed a sharp warming gradient during the last 45 years that was particularly evident in the central and southern regions of the country, which were also the main agricultural areas with high reservoir density. We noted a country-wide progressive increase in average annual cumulative rainfall, but the forcing mechanism of the rainfall increment and its spatial-temporal trends were not fully understood. Climate warming resulted in a significant increase in irrigation water demand, while heavy rains increased runoff generation in the reservoir watersheds. Most reservoirs had reliable storage capacities to meet the demands of a 10-year return frequency drought but the resilience of reservoirs gradually declined over time. This suggests that the recovery time of reservoirs from the failure state had increased which also signifies that the duration of the dry season has been prolonged while the wet season has become shorter and/or more intense. The watershed-irrigated area ratio (W-I_ratio) was critical and the results showed that a slight disruption in reservoir water balance under the influence of future climate change would seriously compromise the performance of reservoirs with W-I_ratio< 5.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.354-359
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• 2006

The analysis of large-scale water resources systems is often complicated by the presence of multiple reservoirs and diversions, the uncertainty of unregulated inflows and demands, and conflicting objectives. Reinforcement learning is presented herein as a new approach to solving the challenging problem of stochastic optimization of multi-reservoir systems. The Q-Learning method, one of the reinforcement learning algorithms, is used for generating integrated monthly operation rules for the Keum River basin in Korea. The Q-Learning model is evaluated by comparing with implicit stochastic dynamic programming and sampling stochastic dynamic programming approaches. Evaluation of the stochastic basin-wide operational models considered several options relating to the choice of hydrologic state and discount factors as well as various stochastic dynamic programming models. The performance of Q-Learning model outperforms the other models in handling of uncertainty of inflows.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.221-221
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• 2012

The WRAP-SALT (Water Rights Analysis Package-SALT) simulation includes computation of end-of-month reservoir storage concentrations and mean monthly reservoir outflow concentrations for each month of the simulation. The model computes reservoir storage loads and concentrations based on load balance accounting algorithms and computes concentrations of water released and withdrawn from a reservoir as a function of the volume-weighted mean concentration of the water stored in the reservoir in the current month or previous months. A load budget accounting of the various component load inflows and outflows entering and leaving a reservoir is performed. A time history of storage concentrations computed for previous months is maintained for use in the lag procedure. This study presents computational methods for routing salinity through reservoirs for incorporation into WRAP-SALT simulation routines and methods for determining values for the parameters of the routing methods.

• Journal of Korea Water Resources Association
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• v.46 no.5
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• pp.519-530
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• 2013

To provide a reliable tool for runoff simulations of ungauged watersheds upstream of reservoirs, a daily runoff simulation model, Tank model, is restructured, the parameter regionalization of the model is conducted, and the model's applicability is evaluated. Taking into account the characteristics of runoffs from the watersheds, a three-tank model is employed. The percolation process of the model's third tank is eliminated, considering the water budgets of the watersheds, and its evapotranspiration component is improved, reflecting the conditions of meteorological observation in South Korea. The sensitivity analysis of the model shows that the model's behaviors, varying with a sensitive parameter, ${\alpha}$, are reasonable. The regional parameter estimation equations are determined, using the characteristics and land uses of the watersheds as variables. The model is applied for the runoff simulations of three watersheds and the water stage simulation of one reservoir, and the simulation results are then compared with the observed values, which prove to be in close agreement with the observations. In addition, the results from simulating inflows of twenty-four reservoirs using the model show that the averages of evapotranspiration rate and runoff rate are 42.8% and 56.6%, respectively, which are resonable. Consequently, it is concluded that the model is practically applicable to simulating runoffs from watersheds upstream of reservoirs, and simulated inflow data are useful for watershed management and reservoir planning, design, and operation.