• Journal of Environmental Science International
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• v.17 no.9
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• pp.1039-1052
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• 2008

The SWAT model developed by the USDA-Agricultural Research service for the prediction of rainfall run-off, sediment, and chemical yields in a basin was applied to Jeju Island watershed to estimate the amount of runoff. The research outcomes revealed that the estimated amount of runoff for the long term on 2 water-sheds showed fairly good performance by the long-term daily runoff simulation. The watershed of Chunmi river located the eastern region in Jeju Island, after calibrations of direct runoff data of 2 surveys, showed the similar values to the existing watershed average runoff rate as 22% of average direct runoff rate for the applied period. The watershed of Oaedo river located the northern region showed $R^2$ of 0.93, RMSE of 14.92 and ME of 0.70 as the result of calibrations by runoff data in the occurrence of 7 rainfalls.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.93-98
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• 2001

This study was performed to analyse the rainfall and the rainfall-runoff characteristics of a rural watershed. The Sangwha basin($105.9km^{2}$) in the Geum river system was selected for this study. The arithmetic mean method, the Thiessen's weighing method, and the isohyetal method were used to analyse areal rainfall distribution and the Huff's quartile method was used to analyse temporal rainfall distribution. In addition, daily runoff analyses were peformed using the DAWAST and tank model. In the model calibration, the data from June through November, 1999 were used. In the model calibration, the observed runoff depth was 513.7mm and runoff rate was 45.2%, and the DAWAST model simulated runoff depth was 608.6mm and runoff rate was 53.5%, and the tank model runoff depth was 596.5mm and runoff rate was 52.5%, respectively. In the model test, the data from June through November, 2000 were used. In the model test, the observed runoff depth was 1032.3mm and runoff rate was 72.5%, and the DAWAST model simulated runoff depth was 871.6mm and runoff rate was 61.3%, and the tank model runoff depth was 825.4mm and runoff rate was 58%, respectively. The DAWAST and tank model's $R^{2}$ and RMSE were 0.85, 3.61mm, and 0.85, 2.77mm in 1999, and 0.83, 5.73mm, and 0.87, 5.39mm in 2000, respectively. Both models predicted low flow runoff better than flood runoff.

• Journal of Wetlands Research
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• v.11 no.3
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• pp.81-88
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• 2009

The cows manure has been used as fertilizers in farmland because of enough nutrients. However, excess nutrients can be washed off during a storm and affected on nearby waterbodies. In this paper, the runoff characteristics from farmland were studied to determine the watershed runoff rate. As results of estimating, watershed runoff rates with short-term runoff are BOD 0.6%, CODcr 0.3 %, CODMn 0.1 %, T-N 0.8 % and T-P 1.0 % On the other hand, they with long-term runoff are BOD 3.6 %, CODcr 1.0 %, CODMn 0.9 %, T-N 4.9 % and T-P 4.8 %. It is clean that the watershed runoff rates increase according to the rainfall runoff time.

• 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.

• Journal of Environmental Health Sciences
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• v.31 no.1
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• pp.1-6
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• 2005

This study was conducted to identify the runoff characteristics of non-point source according to rainfall in Nam watershed. Land-uses of the Nam watershed were surveyed paddy field 4.5%, crop field 6.8%, mountainous 78.7%, urban 2.4%, and etc. 7.7%. Mean runoff coefficients in each area were observed Ⅰ area 0.08, Ⅱ area 0.08, and Ⅲ area 0.05. In the relationship between the rainfall and peak-flow, correlation coefficients(r) were investigated Ⅰ area -0.8609, Ⅱ area 0.6035, and Ⅲ area -0.4913. In the relationship between the antecedent dry period and first flow runoff, correlation coefficients(r) were investigated Ⅰ area -0.9093, Ⅱ area -0.1039, and Ⅲ area -0.7317. The discharge of pollutant concentrations relates to the flow rate of storm-water. In the relationship between the rainfall and watershed loading, exponent values of BOD, COD, SS, and T-N were estimated to 1.2751, 1.2003, 1.3744, and 1.1262, respectively.

• Journal of Environmental Science International
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• v.22 no.5
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• pp.523-531
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• 2013

In this study, a method of simulating ephemeral stream runoff characteristics in Jeju watershed is newly suggested. The process based conceptual-physical scheme is established based on the SWAT-K and applied to Cheonmi-cheon watershed which shows the typical pattern of ephemeral stream runoff characteristics. For the proper simulation of this runoff, the intermediate flow and baseflow are controlled to make downward percolation should be dominant. The result showed that surface runoff simulated by using the modified scheme showed good agreement with observed runoff data. In addition, it was found that the estimated runoff directly affected the groundwater recharge rate. This conceptual model should be continuously progressed including rainfall interception, spatially estimated evapotranspiration and so forth for the reasonable simulation of the hydrologic characteristics in Jeju island.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.200-204
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• 2012

In engineering hydrology, an estimation of precipitation loss is one of the most important issues for successful modeling to forecast flooding or evaluate water resources for both surface and subsurface flows in a watershed. An accurate estimation of precipitation loss is required for successful implementation of rainfall-runoff models. Precipitation loss or hydrological abstraction may be defined as the portion of the precipitation that does not contribute to the direct runoff. It may consist of several loss elements or abstractions of precipitation such as infiltration, depression storage, evaporation or evapotranspiration, and interception. A composite loss rate model that combines four loss rates over time is derived as a lumped form of a continuous time function for a storm event. The composite loss rate model developed is an exponential model similar to Horton's infiltration model, but its parameters have different meanings. In this model, the initial loss rate is related to antecedent precipitation amounts prior to a storm event, and the decay factor of the loss rate is a composite decay of four losses.

• Journal of Korean Society on Water Environment
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• v.26 no.1
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• pp.61-70
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• 2010

The increase of impervious cover (IC) in a watershed is known as an important factor causing alteration of water cycle, deterioration of water quality and biological communities of urban streams. The study objective was to assess the impact of IC changes on the surface runoff characteristics of Kap Stream basin located in Geum river basin (Korea) using the Storm Water Management Model (SWMM). SWMM was calibrated and verified using the flow data observed at outlet of the watershed with 8 days interval in 2007 and 2008. According to the analysis of Landsat satellite imagery data every 5 years from 1975 to 2000, the IC of the watershed has linearly increased from 4.9% to 10.5% during last 25 years. The validated model was applied to simulate the runoff flow rates from the watershed with different IC rates every five years using the climate forcing data of 2007 and 2008. The simulation results indicated that the increase of IC area in the watershed has resulted in the increase of peak runoff and reduction of travel time during flood events. The flood flow ($Q_{95}$) and normal flow ($Q_{180}$) rates of Kap Stream increased with the IC rate. However, the low flow ($Q_{275}$) and drought flow ($Q_{355}$) rates showed no significant difference. Thus the subsurface flow simulation algorithm of the model needs to be revisited for better assessment of the impact of impervious cover on the long-term runoff process.

• Journal of Korea Water Resources Association
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• v.56 no.10
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• pp.655-665
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• 2023

In this study, unit hydrographs are calculated when precipitations of 10 scales instantaneously occurs in a virtual watershed with a constant slope and roughness. Then, the relationship between the peak flow rate and the peak occurrence time of the unit hydrograph was calculated for the precipitation scale, respectively. At this time, the virtual watershed simplified with a rhombic shape, a constant slope, and a flow condition with a certain roughness was applied instead of a natural watershed in order to understand the effect the precipitation scale has on the peak value of the unit hydrograph. And it was assumed that the precipitation in the basin was effective rainfall and the runoff was direct runoff, and the runoff flowed in a straight, uniform flow from the drop point to the outlet. The relationship between the peak flow and the peak occurrence time of the unit hydrograph was calculated in the case of 10 types of precipitation scales of 10 mm, 40 mm, 90 mm, 160 mm, 250 mm, 360 mm, 640 mm, 1,000 mm, 1,210 mm, and 1,690 mm of effective precipitation. A noteworthy achievement of this study is that, even without the storage effect of the watershed, as the scale of precipitation increases, the depth of runoff increases, so the flow rate in the watershed increases and the distance per unit time increases, so the peak flow rate increases and the peak occurrence time increases. This is a nonlinear characteristic of watershed runoff.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.1
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• pp.17-29
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• 2013

Long-Term Hydrologic Impact Assessment (L-THIA) model which is a distributed watershed model was applied to analyze the spatial distribution of surface runoff and nonpoint source pollutant loading from Imha watershed during 2001~2010. L-THIA CN Calibration Tool linked with SCE-UA was developed to calibrate surface runoff automatically. Calibration (2001~2005) and validation (2006~2010) of monthly surface runoff were represented as 'very good' model performance showing 0.91 for calibration and 0.89 for validation as Nash-Sutcliffe (NS) values. Average annual surface runoff from Imha watershed was 218.4 mm and Banbyun subwatershed was much more than other watersheds due to poor hydrologic condition. Average annual nonpoint source pollutant loading from Imha wateshed were 2,295 ton/year for $BOD_5$, 14,752 ton/year for SS, 358 ton/year for T-N, and 79 ton/year for T-P. Amount of pollutant loading and pollutant loading rates from Banbyun watershed were much higher than other watersheds. As results of analysis of loading rate from grid size ($30m{\times}30m$), most of high 10 % of loading rate were generated from upland. Therefore, major hot spot area to manage nonpoint source pollution in Imha watershed is the combination of upland and Banbyun subwatershed. L-THIA model is easy to use and prepare input file and useful tool to manage nonpoint source pollution at screening level.