• 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.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.1
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• pp.40-49
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• 1993

The Objectives of this paper were to develop a modified tank model that is capable of simulating daily streamflow from a small watershed using daily watershed evapotranspiration and to test the applicability of the model to different watersheds. Tank model was restructured to consist of three series of tanks, each of which may mathematically reflect watershed runoff mechanisms from different components of surface runoff, interflow, and baseflow. And pan evaporation was correlated to potential evapotranspiration estimated from a combination method, and was multiplied by monthly crop and landuse coefficients, and watershed storage coefficient to estimate the watershed evapotranspiration losses. Ten watersheds were selected to calibrate model parameters that were defined using an optimization scheme, and the results were correlated with watershed parameters. Simulated daily runoff was compared to the observed ones from the tested watersheds. The simulating results were in good agreement with the observed values when optimal and calibrated parameters were used. Ungaged conditions were also applied to compare simulated values to the observed. And the results were in fair conditions for all the tested watersheds which differ considerably in their sizes, landuse types, and physiological features.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.6
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• pp.177-186
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• 2013

The purpose of this study was to analyze the temporal and spatial characteristics of the stream flow of small rural streams for investigating the status of stream depletion located downstream of irrigation reservoir. Bonghyun and Hai reservoirs and each downstream were selected for this study. Streamflow was measured for 8 stations downstream from two reservoirs from 2010 to 2012. The water quality samples were collected monthly from the 8 stream stations and 2 reservoir stations from 2011 to 2012. The stream depletion was found in most of the downstream of reservoirs for the non-irrigation period and even in the irrigation period when there were a lot of antecedent precipitation. We found that the stream segments where there were few streamflow, vegetation covers the stream and block the streamflow which makes the stream lost its original function as a stream. Water quality monitoring results of Bonghyun stream indicated that the concentration of SS, Turbidity, TOC, COD were decreased as the stream flows from the reservoir to downstream while the TN and TP were increased. The correlation analysis for water quality data indicated that the correlation between T-N and T-P was high for Bonghyeon and Sukji streams, respectively. Continuous monitoring for rural streams located in downstream of reservoirs are required to quantify the status of stream flow depletion and determine the amount of environmental flows.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.118-118
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• 2020

This study investigates the change of flow characteristics over 10 Asian river basins in the past 30 years (1976-2005). The variation is estimated from The Soil and Water Assessment Tool (SWAT) model outputs based on reanalysis data which was bias-corrected for Asian monsoon reagion. The model was firstly calibrated and validated using observed data for daily streamflow. Four statistical criteria were applied to evaluate the model performance, including Coefficient of determination (R2), Nash - Sutcliffe model efficiency coeffi cient (NSE), Root mean square error-observations standard deviation ratio (RSR), and Percentage Bias (PBIAS). Then parameters of the model were applied for the historical period 1976-2005. The estimates show a temporal non-considerable increasing rate of daily streamflow in most of the basins over the past 30 years. The difference of monthly discharge becomes more significant during the months in the wet season (June to September) in all basins. The seasonal runoff shows significant difference in Summer and Autumn, when the rainfall intensity is higher. The line showing averaged runoff/rainfall ratio in all basins is sharp, presenting high variation of seasonal runoff/rainfall ratio from season to season.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.81-88
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• 2010

The analysis and synthesis of various types of hydrologic variables such as precipitation, surface runoff, and discharge are usually required in planning and management of water resources. These hydrologic variables are mostly represented using stochastic models. One of which is the autoregressive model, that gives promising results in time series modeling. This study is an application of this model, which aimed to determine the AR model that best represents the historical monthly streamflow of the two gauging stations, namely Andong Dam and Imha Dam, both located in the upper Nakdong River Basin. AR(3) model was found to be the best model for both gauging stations. Parameters of the determined order of AR model ($\phi_1$, $\phi_2$ and $\phi_3$) were also estimated. Using several diagnostic tests, the efficiency of the determined AR(3) model was tested. These tests indicated the accuracy of the determined AR(3) model.

• Journal of Korea Water Resources Association
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• v.48 no.1
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• pp.69-78
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• 2015

In this study, meteorological drought indices were examined to simulate hydrological drought. SPI (Standardized Precipitation Index) and SPEI (Standardized Precipitation Evapotranspiration Index) was applied to represent meteorological drought. Further, in order to evaluate the hydrological drought, monthly total inflow and SDI (Streamflow Drought Index) was computed. Finally, the correlation between meteorological and hydrological drought indices were analyzed. As a results, in monthly correlation comparison, the correlation between meteorological drought index and monthly total inflow was highest with 0.67 in duration of 270-day. In addition, a meteorological drought index were correlated 0.72 to 0.87 with SDI. In compared to the annual extremes, the relationship between meteorological drought index and minimum monthly inflow was hardly confirmed. But SDI and SPEI showed a slightly higher correlation. There are limitation that analyze extreme hydrological drought using meteorological drought index. For the evaluation of the hydrological drought, drought index which included inflow directly is required.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.249-252
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• 2002

This model is the daily streamflow model of the Korean watersheds has been developed to simulate the daily streamflow with the data of daily rainfall and pan evaporation. Parameters of this model are the water balance parameters composed Umax, Lmax, FC, CP, and CE and the routing parameters composed $U_i,\;k_1\;and\;k_2$. Among these parameters, CE value is applied one fixed value during the year and coefficient of initial ion K is empirically determined by 0.2. The object of this research is to improve the DAWAST model by application of the monthly value of CE for evapotranspiration and the revised K value for the initial abstraction.

• Journal of Korean Society on Water Environment
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• v.26 no.5
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• pp.860-870
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• 2010

Long term monthly monitoring data showed that the water quality of streams flowing into Lake Paldang has been improved by various strategy for water. However, the effect of quality on Lake Paldang is still insufficient because of nonpoint source from watershed. In order to evaluate quantifying methods for pollution source and make a suggestion on improvements, Storm Water Management Model (SWMM) was constructed by using data set from the water quality and streamflow monitoring network in the Kyoungan watershed for Total Maximum Daily Loads (TMDLs). Load duration curve (LDC) based on the result of the Kyoungan watershed SWMM indicated that the water quality criterion on $BOD_5$ was often exceeded in up-stream than down-stream. From flowrate-load correlation curve, SS load significantly increased as streamflow increases. 75.3% of streamflow and 62.1% of $BOD_5$ loads is discharged especially in the zone of high flows, but monitoring data set didn't provide proper information about the conditions and the patterns associated with storm events. Therefore, it is necessary to acquire representative data set for comparing hydrograph and pollutograph through monitoring experimental watershed and to establish methods for quantifying point and nonpoint source pollutant loads.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.605-612
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• 2017

Climate change affects the natural ecosystem and human socioeconomic activities by acting on various constituents such as the atmospheric, oceanic, biological, and land constituents of the climate. Predicting the impacts of ongoing climate change will be an important factor in adapting to the climate of the future. In this study, precipitation-streamflow elasticity analysis of the Nakdong River area was conducted using the RCP 4.5 scenario developed by the IPCC (Intergovernmental Panel on Climate Change). Precipitation and streamflow in the Nakdong River area was analyzed using monthly, seasonal, and yearly data. Results found that the climate would become very humid climate by 2100. Results of this study can be applied to adaptation of climate change, management of water resources and efficient utilization of hydraulic structures.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.329-338
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• 2024

In this study, drought assessment using the standardized precipitation index (SPI) and streamflow drought index (SDI) was conducted for the Inje region, Gangwon Province, South Korea. Monthly streamflow ratios were reviewed through basic data for drought analysis (rainfall, streamflow), and meteorological drought and hydrological drought analysis were conducted using precipitation and water level/flow observation stations near the Inje watershed. The analysis revealed that the drought that occurred in 2014 persisted until 2017 consistently across all drought indices (SPI, SDI). When analyzing drought indices calculated using 12 months of hydrometeorological data, it was found that severe drought lasted for approximately 24 months, indicating that drought damage would have been severe.