• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.205-205
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• 2021

Surface soil moisture, which governs the partitioning of precipitation into infiltration and runoff, plays an important role in the hydrological cycle. The assimilation of satellite soil moisture retrievals into a land surface model or hydrological model has been shown to improve the predictive skill of hydrological variables. This study aims to improve streamflow prediction with Weather Research and Forecasting model-Hydrological modeling system (WRF-Hydro) by assimilating Soil Moisture Active and Passive (SMAP) data at 3 km and analyze its impacts on hydrological components. We applied Cumulative Distribution Function (CDF) technique to remove the bias of SMAP data and assimilate SMAP data (April to July 2015-2019) into WRF-Hydro by using an Ensemble Kalman Filter (EnKF) with a total 12 ensembles. Daily inflow and soil moisture estimates of major dams (Soyanggang, Chungju, Sumjin dam) of South Korea were evaluated. We investigated how hydrologic variables such as runoff, evaporation and soil moisture were better simulated with the data assimilation than without the data assimilation. The result shows that the correlation coefficient of topsoil moisture can be improved, however a change of dam inflow was not outstanding. It may attribute to the fact that soil moisture memory and the respective memory of runoff play on different time scales. These findings demonstrate that the assimilation of satellite soil moisture retrievals can improve the predictive skill of hydrological variables for a better understanding of the water cycle.

• Journal of Korea Water Resources Association
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• v.55 no.12
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• pp.1115-1124
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• 2022

The impact of climate change on water resources was evaluated for Chungju Dam and Soyang-gang Dam basins by constructing an integrated modeling framework consisting of a dam inflow prediction model based on the Variable Infiltration Capacity (VIC) model, a distributed hydrologic model, and an LSTM based dam outflow prediction model. Considering the uncertainty of future climate data, four models of CMIP6 GCM were used as input data of VIC model for future period (2021-2100). As a result of applying future climate data, the average inflow for period increased as the future progressed, and the inflow in the far future (2070-2100) increased by up to 22% compared to that of the observation period (1986-2020). The minimum value of dam discharge lasting 4~50 days was significantly lower than the observed value. This indicates that droughts may occur over a longer period than observed in the past, meaning that citizens of Seoul metropolitan areas may experience severe water shortages due to future droughts. In addition, compared to the near and middle futures, the change in water storage has occurred rapidly in the far future, suggesting that the difficulties of water resource management may increase.

• Economic and Environmental Geology
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• v.49 no.5
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• pp.361-370
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• 2016

It is well known that the inflow of rainwater and the infiltration of groundwater to sewerage (I/I) increase the sewage and burden sewage treatment plants and lower their treatment efficiency. Therefore, it is important to estimate the amount of I/I. In this study, well groundwaters, public water supplies (PWSs), and sewage and rainwater channels were investigated to check whether oxygen and deuterium isotopes could be used as a tool for I/I estimation. This study shows that the isotopic composition of PWS in Jeonju area is very consistent over time and distinctly lighter than the circulating local rainwater (CLR) because it is supplied from Yongdam Dam, which is located about 40 km inland to the east in the mountainous area. Considering the fact that sewage mostly originates from the PWS, we could calculate the amounts of CLR in the sewerage from a monitoring station using unaffected rainwater and tap water as mixing end members. The calculation revealed that the CLR fraction ranged from 50% to 90% depending on observation time. This is well supported by the dilute natures of the sewages at the station. The fraction of PWS in investigated well waters were about 46%, indicating that leaking of PWS is very serious and is an important groundwater source in the study area. Since the infiltration of such groundwater may not alter the isotopic composition of sewage significantly, the actual I/I would be much greater than the calculated ones.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.1-7
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• 1998

To investigate the water balance in a paddy rice field with the pumping station for irrigation water supply, flow measurements and analysis on various components of water balance were carried out. The investigated area is 103.7 ha, and the irrigation water was supplied for 102 days during the total irrigation period starting from June 1. It was found that the consumption rate was increased as the growing stage was progressed. The variation of evapotranspiration rate was shown same tendency as the consumption rate, while no apparent tendency was found in infiltration rate upon different growing stages. And the ground water input to the area was predominant during the early stage of growing period, while ground water output from the study area was predominant at the end of the growing stage. The range of return flow rate, the ratio of total outflow to total inflow in every decad, was 57.6 to 85.7%. These values are slightly higher than reported values from the other investigation projects.

• The Journal of Engineering Geology
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• v.19 no.2
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• pp.205-215
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• 2009

The conventional numerical models to analyze flow in subsurface porous media under the transient state usually generate numerical oscillation and unstability due to local flux domain for critical cases such as infiltration into initially dry soil during rainfall period. In this case, it is required refined mesh and small time step, but it decrease efficiency of computation. In this study, numerical unstability in discontinuity domain is removed by applying particle tracking algorithm to simulate unsteady subsurface flow with inflow boundary condition. Finally the hybrid LE FEM improving numerical stability is proposed. The hypothetical domains with unsteady uniform and nonuniform flow field were used to demonstrated algorithm verification. In comparison with analytic solution, we obtained reasonable results and conducted simulation of hypothetical 3-D recharge/pumping area. The proposed algorithm can simulate saturated/unsaturated porous media with more practical problems and will greatly contribute to accuracy and stability of numerical computation.

• Journal of Environmental Impact Assessment
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• v.18 no.2
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• pp.59-67
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• 2009

Water quality of the Lake Youngrang in the Sokcho City is eutrophic. Jangcheon is the largest inflow source to the lake. Major pollutant sources are stormwater runoff from resort areas and various land uses in the Jangcheon watershed. A storm sewer on the southern end of the lake is also an important pollution source. In this study, water quality modelling for Lake Youngrang was carried out considering the rainfall-runoff pollution loads from the watershed. The rainfall-runoff curves and the rainfall-runoff pollutant load curves were derived from the rainfall-runoff survey data during the recent 4 years. The rainfall-runoff pollution loads and flow from the Jangcheon watershed and the storm sewer were estimated using the two kinds of curves, and they were used as the flow and the boundary data of the WASP model. With the measured water quality data of the year 2005 and 2006, WASP model was calibrated. Non-point pollution control measures such as wet pond and infiltration trench were considered as the alternative for water quality management of the lake. The predicted water quality were compared with those under the present condition, and the improvement effect of the lake water quality were analyzed.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.2
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• pp.179-185
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• 2016

In this study, the RDII predictions were compared using two methodologies, i.e., the RTK-based and regression methods. Long-term (1/1/2011~12/31/2011) monitoring data, which consists of 10-min interval streamflow and the amount of precipitation, were collected at the domestic study area (1.36 km2 located in H county), and used for the construction of the RDII prediction models. The RTK method employs super position of tri-triangles, and each triangle (called, unit hydrograph) is defined by three parameters (i.e., R, T and K) determined/optimized using Genetic Algorithm (GA). In regression method, the MovingAverage (MA) filtering was used for data processing. Accuracies of RDII predictions from these two approaches were evaluated by comparing the root mean square error (RMSE) values from each model, in which the values were calculated to 320.613 (RTK method) and 420.653 (regression method), respectively. As a results, the RTK method was found to be more suitable for RDII prediction during extreme rainfall event, than the regression method.

• Journal of Korea Water Resources Association
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• v.34 no.1
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• pp.91-103
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• 2001

In this studs, hydraulic routing model has been developed to predict the water level and discharge in each river section with considering the full interaction between surface runoff and river flow. It improved the computation of flood runoff by reflecting the shape of hydrograph that was determined by the geological and flood characteristics, and the excessive computation of the peak discharge was eliminated by considering the effect of infiltration. The Inflow from surface runoff to river flow was applied to the equation of continuity by implementing effectively the flow in a number of river section, and resulted in a numerical stability at the rapid variation of rainfall. Measurements were conducted during heavy rain in the watershed area of Yang-Yang Namdae-Chun. The present model was tested to the field, and the computed results were compared to the observed data. Its applicability was confirmed with its verification.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.287-293
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• 2009

The study involved the measurement of flowrate and BOD in the Yeoju area and analyzed annual sewerage data by the I/I analysis technique which is common in Korea. The results of this study are as follows. The I/I for the Y-1 site before maintenance and after the completion of the whole process was reduced from 62% to 16.1% respectively with respect to maximum sewage flow per day. The average quality of water increased. The study measured the Y-2 site from a point of time corresponding to an 80% process rate and its I/I rate went up a little from 8.5% to 11.5%. At the Y-3 site, the I/I rate went up a little from 11% to 13.8%, while little change was noted in the average water quality. At the Y-4 site, the I/I rate was reduced from 43% to 16.9% and its average water quality went up. At the Y-5 site, the I/I quantity went up a little however its average water quality also went up largely. Therefore, it was concluded that the Y-5 site showed great improvement due to the sewer pipe maintenance.

• Korean Journal of Agricultural Science
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• v.47 no.1
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• pp.19-28
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• 2020

This study proposed a simple estimation method for irrigation return flow from paddy fields using the water balance model. The merit of this method is applicability to other paddy fields irrigated from agricultural reservoirs due to the simplicity compared with the previous monitoring based estimation method. It was assumed that the unused amount of irrigation water was the return flow which included the quick and delayed return flows. The amount of irrigation supply from a reservoir was estimated from the reservoir water balance with the storage rate and runoff model. It was also assumed that the infiltration was the main source of the delayed return flow and that the other delayed return flow was neglected. In this study, the amount of reservoir inflow and water demand from paddy field are calculated on a daily basis, and irrigation supply was calculated on 10-day basis, taking into account the uncertainty of the model and the reliability of the data. The regression rate was calculated on a yearly basis, and yearly data was computed by accumulating daily and 10-day data, considering that the recirculating water circulation cycle was relatively long. The proposed method was applied to the paddy blocks of the Jamhong and Seosan agricultural reservoirs and the results were acceptable.