• Journal of The Geomorphological Association of Korea
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• v.28 no.1
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• pp.13-33
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• 2021

Successful sediment management at the watershed scale requires an understanding of the erosion, transport and sedimentation processes at the specific site scale. However, studies on the sediment runoff characteristics in a small uppermost watershed, which serves as a sediment supply function, are very rare. Therefore, this study attempted to investigate the fluctuations in major sediment supply areas and sediment runoff in the uppermost mountain small watershed, and for this purpose, ArcSWAT (Soil and Water Assessment Tools with GIS interface) was applied to the Woldong reservoir catchment located in Gosam-myeon, Anseong-si, Gyeonggi-do. The model results were manually calibrated using the monitoring data of the Woldong reservoir sedimentation rate from 2005 to 2007. It was estimated that annual average of 34.4 tons/year of sediment was discharged from the Woldong reservoir basin. This estimate almost coincided with the monitoring data of the Woldong reservoir during the low flow period but tended to be somewhat underestimated during the high flow period. Although the SWAT model does not fully reflect the erosion process of gully and in-channel, this underestimation is probably due to the spatial connectivity of sediment transport and the storage and reactivation of the sediment being transported. Most of the forested hillslopes with a well-developed organic horizon were evaluated as having a low risk of erosion, while the places with the highest risk of erosion were predicted to be distributed in the logged area with some weeds or shrubs (classified as pasture) with relatively steeper slopes, and in the bare land. The results of this study are expected to be useful in developing strategies for sediment control and reservoir management.

• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.467-473
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• 2007

Although the dominant land use at the Imha-dam watershed is forest areas, soil erosion has been increasing because of intensive agricultural activities performed at the fields located along the stream for easy-access to water supply and relatively favorable topography. In addition, steep topography at the Imha-dam watershed is also contributing increased soil erosion and sediment loads. At the Imha-dam watershed, outflow has increased sharply by the typhoons Rusa and Maemi in 2002, 2003 respectively. In this study, the Soil and Water Assessment Tool (SWAT) model was evaluated for simulation of flow and sediment behaviors with long-term temporal and spatial conditions. The precipitation data from eight precipitation observatories, located at Ilwol, Subi and etc., were used. There was no significant difference in monthly rainfall for 8 locations. However, there was slight differences in rainfall amounts and patterns in 2003 and 2004. The topographical map at 1:5000 scale from the National Geographic Information Institute was used to define watershed boundaries, the detailed soil map at 1:25,000 scale from the National Institute of Highland Agriculture and the land cover data from the Korea Institute of Water and Environment were used to simulate the hydrologic response and soil erosion and sediment behaviors. To evaluate hydrologic component of the SWAT model, calibration was performed for the period from Jan. 2002 to Dec. 2003, and validation for Jan. 2004 to Apr. 2005. The $R^2$ value and El value were 0.93 and 0.90 respectively for calibration period, and the $R^2$ value and El value for validation were 0.73 and 0.68 respectively. The $R^2$ value and El value of sediment yield data with the calibrated parameters was 0.89 and 0.84 respectively. The comparisons with the measured data showed that the SWAT model is applicable to simulate hydrology and sediment behaviors at Imha dam watershed. With proper representation of the Best Management Practices (BM Ps) in the SWAT model, the SWAT can be used for pre-evaluation of the cost-effective and sustainable soil erosion BMPs to solve sediment issues at the Imha-dam watershed. In Korea, the Universal Soil Loss Equation (USLE) has been used to estimate the soil loss for over 30 years. However, there are limitations in the field scale mdel, USLE when applied for watershed. Also, the soil loss changes temporarily and spatially, for example, the Imha-dam watershed. Thus, the SW AT model, capable of simulating hydrologic and soil erosion/sediment behaviors temporarily and spatially at watershed scale, should be used to solve the muddy water issues at the Imha-dam watershed to establish more effective muddy water reduction countermeasure.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.2
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• pp.87-94
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• 2012

This study is to evaluate flood inundation and to recommend measures of damage reduction on sediment by concentrated torrential rainfall at Gonjiamcheon Watershed (183.4 $km^2$). Firstly, the SWAT (Soil and Water Assessment Tool) was simulated streamflow and sediment at upstream. Then, we produced a map of floodplain boundary by using HEC-RAS (Hydrologic Engineering Centers River Analysis System) at downstream. The SWAT model was calibrated with 2 years (2008~2009) daily streamflow and validated for another years (2010~2011. 7. 31). The SWAT model was simulated with 3 years (2008~2010) by monthly water quality (Sediment) at Gonjiamcheon water quality station. The streamflow and sediment from SWAT model were input as boundary conditions to HEC-RAS. The results of HEC-RAS indicated that mapping of floodplain boundary was Jiwol and Jiwol 2 district. Additionally, inundation area and depth were assessed and applied BMPs scenario for managing the sediment yield.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.1
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• pp.99-108
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• 2012

Soil erosion and sediment from agricultural farmland has caused various negative impacts on environment in recent years. The effect of rice straw mat on soil erosion has been investigated by many researchers these days. In this study, the SWAT model was applied to Hongcheon watershed to evaluate SWAT flow and sediment, and the effect of rice straw mat on sediment yield at watershed outlet was evaluated. The Nash-Sutcliffe model efficiency (NSE) and coefficient of determination ($R^2$) values for flow simulation (calibration period) were 0.66 and 0.67, and the NSE values for sediment was 0.90. The calibrated parameters were used to analyze the reduction of sediment yield in the farmland with rice straw mat. Average daily sediment yield without rice straw mat was 49.8 ton/day and sediment yield with rice straw mat was 25.5 ton/day, and the reduction rate was 38.7 %. Also, average daily sediment yield with/without rice straw mat were 97.5 ton/day and 190.7 ton/day during the rainy season (Jun. 2008 - Aug. 2009), with the reduction rate 46.3 %.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.121-130
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• 1993

The major objective of this study is to develop practical methods for estimating sediment yield rates of medium size watersheds of which areas range from 200 to $2,000km^2$. For this purpose, this study adopts an empirical method of statistical approach and another empirical method of weighting the watershed characteristics factors. A total of 13 data points for sediment yield rate, including five data points from reservoir deposit data and eight data points from sampled river-sediment data have been collected. Meanwhile, seven factors that may affect the sediment yield rate of a watershed have been selected. They are drainage density, rainfall erosivity, ground cover and land use, soil erodibility, topography, river-bed material characteristics, and watershed area. In the companion paper following this paper, methods for estimating sediment yield rate are to be developed using the 13 data points collected and seven watershed characteristics factors selected in this study.

• Water Engineering Research
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• v.4 no.3
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• pp.141-154
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• 2003

Nonpoint source pollutants from agriculture are identified as one of the main causes of water quality degradation in the United States. The Hydrological Simulation Program-Fortran (HSPF) was used to simulate runoff, nitrogen, and sediment loads from an urbanizing watershed; the Polecat Creek watershed located in Virginia. Model parameters related to hydrology and water quality were calibrated and validated using observed hydrologic and water quality data collected at the watershed outlet and at several sub-watershed outlets. A comparison of measured and simulated monthly runoff at the outlet of the watershed resulted in a correlation coefficient of 0.94 for the calibration period and 0.74 for the validation period. The annual observed and simulated sediment loads for the calibration period were 220.9 kg/ha and 201.5 kg/ha, respectively. The differences for annual nitrate nitrogen ($NO_3$) loads between the observed and simulated values at the outlet of the watershed were 5.1% and 42.1% for the calibration and validation periods, respectively. The corresponding values for total Kjeldahl nitrogen (TKN) were 60.9% and 40.7%, respectively. Based on the simulation results, the calibrated HSPF input parameters were considered to adequately represent the Polecat Creek watershed.

• Journal of Environmental Impact Assessment
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• v.3 no.2
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• pp.47-56
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• 1994

AGNPS model is an event-based model to analyze nonpoint-source and to examine potential water quality problems from agricultural watershed. This model uses a square grid-cell system to represent the spatial variability of watershed conditions, and simulates runoff, sediment, and nutrient transport for each cell. AGNPS model was applied on Yeonwha watershed, and the test results were compared with the measured data for runoff volume, peak runoff rate, suspended solids, and phosphorus concentration. The watershed of 278.8 ha was divided into 278 cells, each of which was 1 ha in size. The coefficients of determination for runoff volume and peak flow were (0.893 and 0.801 respectively from regression of the estimated values on the measured values. The concentration of suspendid solid was increased but decreased that of phosphate with runoff volume.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.632-636
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• 2005

Accelerated soil erosion is a worldwide problem because of its economic and environmental impacts. To effectively estimate soil erosion and to establish soil erosion management plans, many computer models have been developed and used. The Revised Universal Soil Loss Equation (RUSLE) has been used in many countries, and input parameter data for RUSLE have been well established over the years. However, the RUSLE cannot be used to estimate the sediment yield for a watershed. Thus, the GIS-based Sediment Assessment Tool for Effective Erosion Control (SATEEC) was developed to estimate soil loss and sediment yield for any location within a watershed using the RUSLE and a spatially distributed sediment delivery ratio. SATEEC was enhanced in this study by developing new modules to:1) simulate the effects of sediment retention basins on the receiving water bodies, 2) prepare input parameters for the Web-based sediment decision support system using a GIS interface. This easy-to-operate SATEEC system can be used to identify areas vulnerable to soil loss and to develop efficient soil erosion management plans.

• Journal of Korean Society of Rural Planning
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• v.7 no.1 s.13
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• pp.77-88
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• 2001

In order to evaluate the applicability of GWLF model which can efficiently estimate non-point and point source pollutant loadings in rural watershed including urban district, the model was applied to an experimental watershed. The model was calibrated using observed data such as daily runoffs, sediment yields, T-N, and T-P. Simulated daily runoffs and sediment yields by the model using calibrated parameters were in food agreement with the observed data. There were difference between the simulated and observed nutrient loading which was considered resonable. The simulated results by the model showed that T-N, T-P and sediment yields were dependent on the amount of stream runoff discharge and land use. GWLF model is believed to applicable to estimate amount of pollutant loading of non-point source pollution for the water qualify control of agricultural watersheds.

• Journal of Environmental Impact Assessment
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• v.22 no.6
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• pp.695-703
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• 2013

Soil erosion and sediment delivery ratio(SDR) were estimated by using HSPF model in 3 tributaries of upper stream of Geum river-basin. Meteorological data and other input data were constructed from 2006 to 2011 year by the HSPF model. Flow and suspended solid results were relatively matched with the measurement data through the calibration and validation of the model. Soil erosion was proportional to the amount of rainfall and the area of watershed based on the results of model calibration and validation. SDR in Moojunamdea stream was the highest and one in Cho stream was the lowest. This was effected by the geographical characteristic. SDR was 17.6% Moojunamdea stream, 9.1% Cho stream and 13.2 % Bocheong stream. As the SDR was effected by watershed area and shape factor in this study area.