• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.2
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• pp.49-60
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• 2007

The alpine agricultural activities are usually performed at higher and steep areas in nature. Thus, significant amounts of soil erosion are occurring compared with those from other areas. Thus, the soil erosion induced environmental impacts in these areas are getting greater. The Doam watershed is located at alpine areas and it has been well known that the agricultural activities in the watershed are causing accelerated soil erosion and water quality degradations. Many modeling approaches were employed to solve soil erosion and water quality issues. In this study, the Soil and Water Assessment Tool (SWAT) model was utilized to simulate the hydrologic and sediment behaviors in the Doam watershed. In many previous modeling studies, the digital soil map and its corresponding soil properties were used without modification to reflect soil conditioning at many agricultural fields of the Doam watershed. Thus, the soil sample was taken at the agricultural field within the Doam watershed and analyzed for its physical properties. In this study, the digital topsoil properties in the agricultural fields within the Doam watershed were replaced with the soil properties for reconditioned soil analyzed in this study to simulate the impacts of using soil properties for reconditioned soil in hydrologic and sediment modeling at the Doam watershed using the SWAT model. The hydrologic component of the SWAT model was calibrated and validated for measured flow data from 2002 to 2003. The $R^2$ value was 0.79 and the EI value was 0.53 for weekly simulated data. The calibrated model parameters were used for hydrologic component validation and the $R^2$ value was 0.86 and the EI value was 0.74 for weekly data. For sediment comparison, the $R^2$ value was 0.67 and the EI value was 0.59. These statistics improved with the use of soil properties of the reconditioned soil in the field compared with the results obtained without considering soil reconditioning. The simulated sediment amounts with and without considering the soil properties of the reconditioned soil were 284,813 ton and 158,369 ton, respectively. This result indicates that there could be approximately 79% of errors in estimated sediment yield at the Doam watershed, although the model comparison with the measured data gave similar satisfactory statistics with and without considering soil properties from the reconditioned soil.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.6
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• pp.39-48
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• 2010

Sediment yields from Imha watershed were simulated during 1993-2008 using Hydrologic Simulation Program-Fortran (HSPF). Using observed daily stream flow for 2004-2008 and hourly suspended solid concentration for three events during 2006, HSPF was calibrated and validated at the sites of Imha and Youngyang for stream flow and Dongchun and Jangpachun for sediment yield. The calibration and validation results represented high model efficiency for simulating daily stream flow and hourly suspended solid. The determination coefficients of calibration and validation were 0.90 and 0.81 for daily stream flow, and 0.91 and 0.86 for monthly stream flow, respectively. Based on model tolerances for calibration and validation of stream flow, HSPF performance for simulating stream flow represented 'very good'. The determination coefficients of calibration and validation were 0.94-0.96 and 0.95 for hourly sediment yields, respectively. The average yearly sediment yield during 1993-2008 was 122,290 ton/year and most of sediment yield (77 % of total yield) were generated from June to August. The calibrated HSPF simulated well the movement of water and eroded soil within Imha watershed.

• KCID journal
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• v.14 no.1
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• pp.50-56
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• 2007

In this study, the Soil and Water Assessment Tool (SWAT) model was used to assess spatiotemporal effects on watershed runoff and sediment characteristics due to land uses changes from 1999 to 2002 at the small watershed, located in Chuncheon-si, Gangwon province. The annual average flow rate of Scenario I (long-term simulation using land use of 1990), II (long-term simulation using land use of 1996), III(long-term simulation using land use of 200) and IV(simulation using land use of 1990, 1995, and 2000) in long-term simulation) using the SWAT model were 29,997,043 m3, 29,992,628 m3, 29,811,191 m3 and 29,931,238 m3, respectively. It was shown that there was no significant changes in estimated flow rate because no significant changes in land uses between 1990 and 2000 were observed. The annual average sediment loads of Scenarios I, II, III and IV for 15 year period were 36,643 kg/ha, 45,340 kg/ha , 27,195 kg/ha and 35,545 kg/ha, respectively. The estimated annual sediment loads from Scenarios I, II, and III, were different from that from the scenario IV, considering spatio-temporal changes in land use and meterological changes over the years, by 10%, 127%, and temporal changes in land use and meterological changes over the years, by 10%, 127%, and 77%. This can be explained in land use changes in high soil erosion potential areas, such as upland areas, within the study watershed. The comparison indicates that changes in land uses upland areas, within the study watershed. The comparison indicates that changes in land uses can affect on sediment yields by more than 10%, which could exceed the safety factor of 10% in Total Maximum Daily Loads (TMDLs). It is, therefore, recommended that not only the temporal analysis with the weather input data but also spatial one with different land uses need to be considered in long-term hydrology and sediment simulating using the SWAT model

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.327-327
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• 2020

Increase in Earth's surface temperature, higher rainfall intensity rate, and rapid changes in land cover are just some of the most evident effects of climate change. Flooding, and river sedimentation are two inevitable natural processes in our environment, and both issues poses great risks in the dam industry when not addressed properly. River sedimentation is a significant issue that causes reservoir deposition, and thus causes the dam to gradually lose its ability to store water. In this study, the long-term effects of climate change on the sediment discharge in Yongdam Dam watershed is analyzed through the utilization of SWAT, a semi-distributed watershed model. Based from the results of this study, an abrupt increase on the annual sediment inflow trend in Yongdam Dam watershed was observed; which may suggests that due to the effects of climate change, higher rainfall intensity, land use and land cover changes, the sedimentation rate also increased. An efficient sedimentation management should consider the increasing trend in sedimentation rate due to the effects of climate change.

• Journal of Wetlands Research
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• v.19 no.1
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• pp.132-143
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• 2017

It is essential to obtain periodic sediment discharge data in a river in order to minimize problems that may arise from the erosion, transport, and deposition of sediment. However, it is difficult to estimate sediment discharge by the sediment discharge measurement plan in Korea at present, and empirical fomulas or numerical models are used to replace them. This paper has applied the K-DRUM model, a grid-based rainfall-runoff-sediment model, to estimate sediment discharge and ensure the continuity of the data in the watershed. Discharge and sediment load in 17 watersheds were estimated and the applicability of the model was analyzed through comparisons with measured data. For quantitative evaluation, NSE, PBIAS and RSR items were used, and discharge results reflected the tendency of rainfall and showed high statistical value. In case of sediment discharge, the soil erosion process of the watershed is physically well reflected. When the calibration was performed using the measure data, the applicability seems to be excellent in estimating the continuous sediment discharge data in the real watershed.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2003.10a
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• pp.527-530
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• 2003

In this study, physically based SWAT model was applied to estimate the daily stream flows and sediment yields in Gyeongancheon watershed. The calibration and validation of the model outputs have been performed with yearly and daily measured stream flows of the time period 1988-1991 and 2001. The application results showed a good agreement with the simulated and observed stream flows, and similar trend with simulated and observed sediment yields. Overall, SWAT is a reasonable watershed scale model on long-term simulations of stream flows and sediment yields for management purposes.

• Magazine of the Korean Society of Agricultural Engineers
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• v.30 no.4
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• pp.45-61
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• 1988

The purpose of this study is to develop regression equations between annual specific sedi- ment of reservoirs and physiographic factors of watersheds. 122 irrigation reservoirs, which have irrigation areas equal to or larger than 200 ha, located in Korea except Cheju province are used in the analysis. Simple regression analyses between the specific annual sediment and each of the physical characteristic factors of the reservoirs are carried out at first. Then, multiple regression analyses between the annual specific sediment and the physical characteristic factors with high correlation coefficients in the simple regression analyses are made. The results obtained from this study are as follows : 1. The results of the sirnple regression analyses show that in each province the watershed area, the length of mainstream, the circumferential length of watershed have high cor- relation coefficients (R=0.814-0.986), and that drainage density, reservoir capacity per watershed area, drainage frequency, basin relief have low correlation coefficients (R=0. 387-0.955). 2. The purposed multiple regression equations between the annual specific sediment of reservoirs and three major characteritic factors of watersheds, namely, the watershed area, the circumferential length of watershed, and the length of mainstream, are proposed as given in Table 2. 3. The result of the simple regression analyses with respect to the reservoir elevation except Jeonnam province, which has very different characteristics comparing to other provinces, shows that watershed area, main stream length and circumferential length have high correlation coefficients (R=0.806-0.884) in low-elevation reservoirs and intermediate- elevation reservoirs, but low correlation coefficients (R=0.639-0.739) in high-elevation reservoirs. 4. With respect to the reservoir elevation, the proposed multiple regression equations bet- ween the annual specific sediment of reservoirs and the three major characteristic factors of watershed which have high correlation coefficients are proposed as given in Table 5.

• Journal of Korea Water Resources Association
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• v.36 no.6
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• pp.1059-1068
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• 2003

Geographic Information System (GIS) combined with Universal Soil Loss Equation (USLE) was used to estimate the soil erosion of Asan Bay experiment watershed in Korea. Spatial data for each USLE factors were obtained from the Landsat-5 TM remote sensing images and 1/25,000 scale digital contour maps. Sediment yield to Asan Bay was estimated by the sediment delivery ratio and trap efficiency. The estimated sediment yield was compared with observed on the Asan and Sapgyo estuary sub-watershed within Asan Bay experimental watershed for the period from 1981 to 2000. The calculated total annual sediment yields from Asan and Sapgyo estuary sub-watershed to Asan Bay were 5,665tonnes/yr and 6,766tonnes/yr, respectively. The measured sediment yields were 12,937tonnes/yr and 12,395tonnes/yr, respectively on an average.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.6
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• pp.983-990
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• 2011

Universal Soil Loss Equation (USLE) has been used to estimate potential long-term soil erosion in the fields. However, the USLE does not estimate sediment yield due to lack of module considering sediment delivery ratio (SDR) for watershed application. For that reason, the Sediment Assessment Tool for Effective Erosion Control (SATEEC) system was developed and applied to compute the sediment yield at watershed scale. However, the R factor of current SATEEC Ver. 2.1 was estimated based on 5-day antecedent rainfall, it is not related with fundamental concept of R factor. To compute R factor accurately, the energy of rainfall strikes should be considered. In this study, the R module in the SATEEC system was enhanced using formulas of Williams, Foster, Cooley, CREAMS which could consider the energy of rainfall strikes. The enhanced SATEEC system ver. 2.2 was applied to the Imha watershed and monthly sediment yield was estimated. As a result of this study, the $R^2$ and NSE values are 0.591 and 0.573 for calibration period, and 0.927 and 0.911 for validation period, respectively. The results demonstrate the enhanced SATEEC System estimates the sediment yield suitably, and it could be used to establish the detailed environmental policy standard using USLE input dataset at watershed scale.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.752-757
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• 2009

In the last decade, many methods such as greet chamber, reservoir, or debris barrier, have been utilized to manage and prevent muddy water problem. The Vegetative Filter Strip (VFS) has been thought to be one of the most effective methods to trap sediment effectively. The VFS are usually installed at the edge of agricultural areas adjacent to stream or drainage ditches, and it has been shown that the VFS effectively removes pollutants transported with upland runoff. But, if the VFS is installed without any scientific analysis of rainfall-runoff characteristics, soil erosion, and sediment analysis, it may not reduce the sediment as much as expected. Although Soil and Water Assessment Tool (SWAT) model has been used worldwide for many hydrologic and Non-Point Source Pollution (NPSP) analysis at a watershed scale. but it has many limitations in simulating the VFS. Because it considers only 'filter strip width' when the model estimates sediment trapping efficiency, and does not consider the routing of sediment with overland flow option which is expected to maximize the sediment trapping efficiency from upper agricultural subbasin to lower spatially-explicit filter strip. Therefore, the SWAT overland flow option between landuse-subbasins with sediment routing capability was enhanced with modifications in SWAT watershed configuration and SWAT engine. The enhanced SWAT can simulate the sediment trapping efficiency of the VFS in the similar way as the desktop VFSMOD-w system does. Also it now can simulate the effects of overland flow from upper subbasin to reflect the increased runoff volume at the receiving subbasin, which is what is occurring at the field if no diversion channel is installed. In this study, the enhanced SWAT model was applied to small watershed located at Jaun-ri in South Korea to simulate diversion channel and spatially-explicit VFS. It was found that approximately sediment can be reduced by 31%, 65%, 68%, with diversion channel, the VFS, and the VFS with diversion channel, respectively.