• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.1
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• pp.21-29
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• 2019

This study analyzed the variability of drought risk based on trend analysis of dry-seasonal dam inflow located in upper river basins. To this, we used areal averaged precipitation and dam inflow of three upper river dams such as Soyang dam, Chungju dam, and Andong dam. We employed Mann-Kendall trend analysis and change point detection method to identify the significant trends and changing point in time series. Our results showed that significant decreasing trends (95% confidence interval) in dry-seasonal runoff rates (= dam inflow/precipitation) in three-dam basins. We investigated potential causes of decreasing runoff rates trends using changes in potential evapotranspiration (PET) and precipitation indices. However, there were no clear relation among changes in runoff rates, PET, and precipitation indices. Runoff rate reduction in the three dams may increase the risk of dam operational management and long-term water resource planning. Therefore, it will be necessary to perform a multilateral analysis to better understand decreasing runoff rates.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.143-148
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• 2010

In this study, the mixed model of the surface rainfall-runoff analysis using grid data and Illudas model was applied to the urban watershed of Bulgang river. After the surface rainfall-runoff was estimated with GIS data, the runoff hydrograph was calculated using network analysis at Jeungsan bridge, which is the final output of watershed. Estimated runoff hydrograph in this study was compared to the observed runoff hydrograph which is converted from the water stage at Jeungsan bridge. The relative errors of total runoff volume and peak discharge showed the range values of 11.70%~16.30% and 1.10%~6.96%, and then the difference of peak times had the values of less than 1 hour for 4 storms. Therefore, the mixed model in this study could be considered to estimate the runoff hydrograph for the prevention of disasters in urban watershed.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.3
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• pp.59-68
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• 2005

The rainfall-runoff potential of Jangseong reservoir watershed was studied based on SCS (Soil Conservation Service, which is now the NRCS, Natural Resources Conservation Service, USDA) runoff curve number (CN) technique. Precipitation and reservoir operation data had been collected. The rainfall-runoff pairs from the watershed for ten years was estimated using reservoir water balance analysis using reservoir operation records. The maximum retention, S, for each storm event from rainfall-runoff pair was estimated for selected storm events. The estimated S values were arranged in descending order, then its probability distribution was determined as log-normal distribution, and associated CNs were found about probability levels of Pr=0.1, 0.5, and 0.9, respectively. A subwatershed that has the similar portions of land use categories to the whole watershed of Jangseong reservoir was selected and hydrologic monitoring was conducted. CNs for subwatershed were determined using observed data. CNs determined from observed rainfall-runoff data and reservoir water balance analysis were compared to the suggested CNs by the method of SCS-NEH4. The $CN_{II}$ measured and estimated from water balance analysis in this study were 78.0 and 78.1, respectively. However, the $CN_{II}$, which was determined based on hydrologic soil group, land use, was 67.2 indicating that actual runoff potential of Jangseong reservoir watershed is higher than that evaluated by SCS-NEH4 method. The results showed that watershed runoff potential for large scale agricultural reservoirs needs to be examined for efficient management of water resources and flood prevention.

• Journal of Environmental Science International
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• v.19 no.10
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• pp.1211-1217
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• 2010

For an accurate rainfall-runoff simulation in the river basin, it is important to consider not only evaluation of runoff model but also accurate runoff component. In this study long-term runoffs were simulated by means of watershed runoff model and the amounts of runoff components such as upstream inflow, surface runoff, return flow and dam release were evaluated based on the concept of water budget. SSARR model was applied to Daecheong basin, the upstream region of Geum river basin, and in turn the monthly runoff discharges of main control points in the basin were analyzed. In addition, for the purpose of providing the basic quantified water resources data the conceptual runoff amounts were estimated with water budget analysis and the reliability of the observations and the monthly runoff characteristics were investigated in depth. The yearly runoff ratios were also estimated and compared with the observations. From the results of the main control points, Yongdam, Hotan, Okcheon and Daecheong, the yearly runoff ratios of those points are consistent well with data reported previously.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.3
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• pp.91-98
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• 1998

In this study, the hydrological changes due to urbanization were investigated and fundamental theory and characteristics of typical urban runoff model such as ILLUDAS was studied. Above model was applied for urbanizing Dongsucheon basin, Incheon. The main parameters (II, IA, IS) which are included in model depending on runoff results were determined, and dimensionless values such as total runoff ratio($Q_{TR}$), peak runoff ratio($Q_{PR}$), and runoff sensitivity ratio ($Q_{SR}=Q_{TR}/Q_{PR}$) were estimated in order to evaluate and compare the characteristics of model based on relative sensitivity analysis.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.5
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• pp.54-66
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• 2002

A grid-based hydrological model, CELTHYM, capable of estimating base flow and surface runoff using only readily available data, was used to assess hydrologic impacts caused by land use change on Little Eagle Creek (LEC) in Central Indiana. Using time periods when land use data are available, the model was calibrated with two years of observed stream flow data, 1983-1984, and verified by comparison of model predictions with observed stream flow data for 1972-1974 and 1990-1992. Stream flow data were separated into direct runoff and base flow using HYSEP (USGS) to estimate the impacts of urbanization on each hydrologic component. Analysis of the ratio between direct runoff and total runoff from simulation results, and the change in these ratios with land use change, shows that the ratio of direct runoff increases proportionally with increasing urban area. The ratio of direct runoff also varies with annual rainfall, with dry year ratios larger than those for wet years shows that urbanization might be more harmful during dry years than abundant rainfall years in terms of water yield and water quality management.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.2
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• pp.74-81
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• 1999

In this study, the hydrological changes due to urbanization were investigated and fundamental theory and characteristics of typical urban runoff model such as CHICAGO Model was studied. Above model was applied for urbanizing Dongsucheon basin, Incheon. The main parameters(CI, CP, CS) which are included in this model depending on runoff results were determined, and dimensionless values such as total runoff ratio($Q_{TR}$), peak runoff ratio($Q_{PR}$), and runoff sensitivity ratio($Q_{SR}=Q_{TR}/Q_{PR}$) were estimated in order to evaluate and compare the characteristics of model based on relative sensitivity analysis. Finally, applied model was proposed based on understanding of work types and established urban runoff models which can simulate well for areal development patterns and urban river basin.

• Journal of Korean Society of Water and Wastewater
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• v.11 no.4
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• pp.80-90
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• 1997

The ILLUDAS and SWMM models were applied to the developing area of Dongsucheon for comparisons of the total runoff, peak discharge and travel time. For this purpose, the present and future urbanization rates were assumed 70% and 90%, respectively. The runoff analysis of two models has been performed based on 10, 20, 30 and 50 return periods and Huff's 4 quantiles for time distribution pattern of design rainfalls. As results, the total runoff based on Huff's pattern had an decreasing order of 1, 4, 3 and 2 quantiles for both models. The SWMM model showed that there were 4.3% increasing of the total runoff, 4.9% increasing of peak discharge, and 6.6% decreasing of travel time. Similarly, for ILLUDAS model, there were 7.3% and 9.2% increasing of total runoff and peak discharge, respectively and 9.1% decreasing of travel time.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.105-114
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• 2009

With urbanization in many countries, many pervious areas are being converted into impervious areas. These land use changes cause many negative impacts on runoff and water quality in the areas. Especially runoff volume and peak runoff are increasing with urbanization. In addition to the increased runoff, more pollutant transports to the downstream areas. For these reasons, Low Impact Development (LID) are nowadays being introduced in urban planning. For environment-friendly and economical urban development, the LID Integrated Management Practices (IMPs) are applied in various urban development. However, exact effects on runoff and water quality of various LID IMPs are not assessed with proper LID evaluation technique. Thus, the SWMM (Storm Water Management Model) 5.0 model was slightly modified to simulate the effect of infiltration manhole on runoff and water quality. For comparison of runoff and TSS (Total Suspended Solids) from the study area (26.5 ha), three scenarios were made in this study. It was found that runoff volume, peak runoff, and TSS could be reduced with infiltration manholes and pervious pavements to some degree. Although, there are many limitations in the analysis of LID effects on runoff and TSS, similar trends shown in this study would be expected with site-specific LID IMPs. Thus, it is strongly recommended that various site-specific LID IMPs, such as infiltration facilities, should be applied as much as possible for environment-friendly urban planning.

• Journal of Environmental Science International
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• v.24 no.4
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• pp.437-447
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• 2015

Estimation of runoff peak is needed to assess water availability, in order to support the multifaceted water uses and functions, hence to underscore the modalities for efficient water utilization. The magnitude of storm rainfall acts as a primary input for basin level runoff computation. The rainfall-runoff linkage plays a pivotal role in water resource system management and feasibility level planning for resource distribution. Considering this importance, a case study has been carried out in the Hancheon basin of Jeju Island where distinctive hydrological characteristics are investigated for continuous storm rainfall and high permeable geological features. The study aims to estimate unit hydrograph parameters, peak runoff and peak time of storm rainfalls based on Clark unit hydrograph method. For analyzing observed runoff, five storm rainfall events were selected randomly from recent years' rainfall and HEC-hydrologic modeling system (HMS) model was used for rainfall-runoff data processing. The simulation results showed that the peak runoff varies from 164 to 548 m3/sec and peak time (onset) varies from 8 to 27 hours. A comprehensive relationship between Clark unit hydrograph parameters (time of concentration and storage coefficient) has also been derived in this study. The optimized values of the two parameters were verified by the analysis of variance (ANOVA) and runoff comparison performance were analyzed by root mean square error (RMSE) and Nash-Sutcliffe efficiency (NSE) estimation. After statistical analysis of the Clark parameters significance level was found in 5% and runoff performances were found as 3.97 RMSE and 0.99 NSE, respectively. The calibration and validation results indicated strong coherence of unit hydrograph model responses to the actual situation of historical storm runoff events.