• Journal of Korea Water Resources Association
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• v.34 no.2
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• pp.131-140
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• 2001

The present study is focused on improving the methodology for the determination of parameters involved in USLE(Universal Soil Loss Equation) based on distributed system concept and investigation of sediment delivery ratio. Generally the distributed system concept consists of grid networks throughout the watershed and sediment can be traced from grid to rid in the direction of the steepest descent. The sediment yield data together with physical data of 10 small irrigation reservoirs in Kyounggi-Do are collected. After the sediment delivery ratio of a grid is defined to be related tothe fraction of forested or covered with delivery proofing area of the grid, the preportionality coefficient(C$_1$) is introduced. The distributed system model is calibrated using the available data for 8 reservoirs and is verified with the data for the ramaining 2 reservoirs, and regression analysis is made to express the proportionality coefficient $C_1$ in terms of watershed physical characteristics. By applying this results the verification of the distributed system model for 2 reservoirs showed a fair result, which justifies the applicability of the proposed method in the present study.

• 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

• Journal of Korean Society on Water Environment
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• v.37 no.2
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• pp.103-113
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• 2021

In this study, an Excel-based model (ROADMOD) was developed to estimate pollutant loading from the road and evaluate BMPs. ROADMOD employs the Chezy-Manning equation and empirical expression for estimating surface runoff, and power function for pollutant buildup, and exponential function for pollutant washoff in SWMM. The results of model calibration for buildup and washoff using observed data revealed a good match between the simulation results and the observed data. The long-term surface runoff and sediment simulated by ROADMOD demonstrated a good match with those by SWMM with 2 ~ 14% of relative error. The shorter sweeping interval (within 8 days) remarkably decreased sediment loads from the road. It was found that the effect of reducing sediment loads from the road was greatly affected not only by the sweeping interval but also by sweeping on the day before a rainfall event. The 48% of removal efficiency of sediment loads from the road was achieved with 26 times of road sweeping per year when sweeping was performed on the day before the rainfall event. A 4-day sweeping interval showed similar removal efficiency (48%) with 96 times of sweeping per year. It is considered that the road sweeping on the day before a rainfall event could maximize the effect of reducing the non-point source pollution from the road with minimization of the number of road sweeping. So, the road sweeping on the day before a rainfall event can be considered as one of the useful and best management practices (BMPs) on road.

• Journal of Korean Society on Water Environment
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• v.40 no.5
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• pp.215-228
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• 2024

Lakes are one of major sources of methane gas due to anaerobic decomposition of organic matter in sediments. Since methane released from lakes is a greenhouse gas, it is necessary to investigate factors affecting methane production of lakes. This study conducted field and incubation experiments in Lake Asan in August and October to determine effects of thermal stratification and sediment organic matter characteristics on methane production. Field experiments measured temperature and dissolved oxygen to determine the formation of thermal stratification of lakes. Methane and organic matter characteristics were analyzed using gas chromatography, Total Organic Carbon (TOC) analyzers, and fluorescence spectroscopy. Incubation experiments under anaerobic conditions used sediment and water samples from the same site. Field results showed higher methane fluxes in August and increased Dissolved Organic Carbon (DOC) concentration closer to Asan Bay seawall. Elevated methane fluxes and DOC concentration resulted from intensified anaerobic decomposition formed by thermal stratification. Incubation results indicated that sediment organic matter characteristics influenced methane flux between sites. Statistical analysis revealed that thermal stratification could be a primary factor affecting methane production of lakes. Characteristics of sediment organic matter with respect to quantity and quality could be factors influencing methane production of lakes. Results of this study can serve as fundamental data for predicting methane emissions from lakes due to climate change and for mitigating lake's contributions to global warming.

• Journal of Ocean Engineering and Technology
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• v.33 no.6
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• pp.564-572
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• 2019

Numerical simulation of the sediment by the Delft3d model was conducted to examine the changes in the sediment budget transport caused by long-term wave changes at the Maengbang beach. Representative waves were generated with input reduction tools using NOAA NCEP wave data for about 40 years, i.e., from January 1979 to May 2019. To determine the adequacy of the model, wave and depth changes were compared and verified using wave and depth data observed for about 23 months beginning in March 2017. As a result of the error analysis, the bias was 0.05 and the root mean square error was 0.23, which indicated that the numerical wave results were satisfactory. Also, the observed change in depth and numerical result were similar. In addition, to examine the effect due to long-term changes in the waves, the NOAA wave data classified into each of the representative wave grades, and then the annual trend of the representative wave was analyzed. After deciding the weight of each wave class considering the changed wave environment in 2100, the amounts of sedimentation, deposition, and the sediment transport budget were reviewed for the same period. The results indicated that the sedimentation pattern did not change significantly compared to the current state, and the amount of the local sediment budget shown in the present state was slightly less. And there has been a local increase in the number of sediment budget transport, but there is no significant difference in the net and amount of sediment movements.

• Journal of Korea Water Resources Association
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• v.49 no.12
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• pp.971-980
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• 2016

In general, efficient operation of sediment sluicing is important in economical aspect. In this study, the efficiency of sediment sluicing by various operation at water surface elevation on multi-functional weirs were analyzed using Nays2DH, and we focused on the Dalsung weir at Nakdong river. The results of this study shows that, the same number of flushing channels and water gates were developed due to sediment sluicing, and sediment deposition occurred in upstream region of flushing channels. Also, the sediment sluicing efficiency increased by approximately 4.6% and sedimentation decreased by approximately 4.5% at EL. 14.5 m for operations on water surface elevation exceeding EL. 14.0 m. The mitigation of reservoir sedimentation and extension of maintenance dredging period are possible if the variation of sediment sluicing efficiency in various operation at water surface elevation during flood season are considered.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.1
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• pp.45-52
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• 2020

Even though sewers have been conventionally designed to prevent from sediment deposition using a specified minimum velocity or shear stress at a particular depth of flow or with a particular frequency of occurrence, it was appreciated that these methods do not consider the characteristics and concentration of the sediment and the specific hydraulic conditions of the sewer with sediment. In this study, a densimetric Froude number formula was suggested considering particle diameter and volumetric concentration of the sediment as well as flow depth and flowrate, based on several domestic field inspections, which was compared with other formulas proposed by previous investigators. When the sediment concentration was not considered, the calibration coefficient of 0.125-1.5 to the densimetric Froude numbers of this study was needed to obtain the similar ones with previous investigators'. For the densimetric Froude number formula obtained with consideration of sediment concentration, the exponent value of term C_v was almost the same as that of previous results and that of d₅₀/R_h was similar for F_r < 2.2.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.111-117
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• 2009

The RUSLE(Revised Universal Soil Loss Equation) has been most widely used to estimate sediment yield in Korea. However RUSLE factors have not been verified based on measured data of sediment yield. The analysis of characteristics for the rainfall erosivity factor R was performed in this study. The R factor of RUSLE is expressed as multiple of total rainfall energy and maximum 30 min rainfall intensity. In this study, the characteristics of 10 rainfall energy equations were investigated using data measured in Gangneung experimental watershed, and applicability of each equations was reviewed based on results of the correlation analysis between measured sediment yield and total rainfall, between measured sediment yield and maximum intensity, and between measured sediment yield and total rainfall energy yield. Also, the relationship of I30 and I60 was proposed using 10-min rainfall data during 9 years.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.194-198
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• 2008

Significant soil erosion and water quality degradation issues are occurring at highland agricultural areas of Kangwon province because of agronomic and topographical specialities of the region. Thus spatial and temporal modeling techniques are often utilized to analyze soil erosion and sediment behaviors at watershed scale. The Soil and Water Assessment Tool (SWAT) model is one of the watershed scale models that have been widely used for these ends in Korea. In most cases, the SWAT users tend to use the readily available input dataset, such as the Ministry of Environment (MOE) land cover data ignoring temporal and spatial changes in land cover. Spatial and temporal resolutions of the MOE land cover data are not good enough to reflect field condition for accurate assesment of soil erosion and sediment behaviors. Especially accelerated soil erosion is occurring from agricultural fields, which is sometimes not possible to identify with low-resolution MOD land cover data. Thus new land cover data is prepared with cadastral map and high spatial resolution images of the Doam-dam watershed. The SWAT model was calibrated and validated with this land cover data. The EI values were 0.79 and 0.85 for streamflow calibration and validation, respectively. The EI were 0.79 and 0.86 for sediment calibration and validation, respectively. These EI values were greater than those with MOE land cover data. With newly prepared land cover dataset for the Doam-dam watershed, the SWAT model better predicts hydrologic and sediment behaviors. The number of HRUs with new land cover data increased by 70.2% compared with that with the MOE land cover, indicating better representation of small-sized agricultural field boundaries. The SWAT estimated annual average sediment yield with the MOE land cover data was 61.8 ton/ha/year for the Doam-dam watershed, while 36.2 ton/ha/year (70.7% difference) of annual sediment yield with new land cover data. Especially the most significant difference in estimated sediment yield was 548.0% for the subwatershed #2 (165.9 ton/ha/year with the MOE land cover data and 25.6 ton/ha/year with new land cover data developed in this study). The results obtained in this study implies that the use of MOE land cover data in SWAT sediment simulation for the Doam-dam watershed could results in 70.7% differences in overall sediment estimation and incorrect identification of sediment hot spot areas (such as subwatershed #2) for effective sediment management. Therefore it is recommended that one needs to carefully validate land cover for the study watershed for accurate hydrologic and sediment simulation with the SWAT model.

• Journal of Korea Water Resources Association
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• v.44 no.12
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• pp.975-990
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• 2011

In this study, to develop an assessment method for spatio-temporal riverbed changes, a 1-dimensional model (HEC-RAS) and a 2-dimensional model (CCHE2D) were built and applied. As for the analysis of a riverbed's long-term change in a real stream, three new assessment methods were developed, which are called the "Sediment section cumulative curve", "Sediment section moment", and "Sediment probability distribution function." These methods were used to assess the characteristics of riverbed changes using a consistent valuation standard and to understand changes in quantities intuitively. From the results of this study, sediment characteristics of cross sections can be detected effectively by applying the "Sediment section cumulative curve" method to determine whether there is any sedimentation or erosion in total emission. The amount of sedimentation or erosion occurring in the right or left banks, which divided by center column, could be presented as one criterion by applying the "Sediment section moment" method. This approach could be utilized as an indicator for sediment predictions. Spatio-temporal sediment variables can be presented quantitatively by determining the mean and uncertain boundaries through the "Sediment probability distribution function", and finally, the results can be illustrated for each cross section to provide intuitive recognition.