• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.26-41
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• 2016

Catchment Hydrologic Cycle Assess Tool (CAT) is a model for hydrologic cycle assessment based on physical parameters. In this study, CAT was applied for short-term runoff simulation and connected with model-independent parameter estimation (PEST) for auto-calibrating parameters. The model performance was compared with HEC-HMS, which is widely used for short-term runoff simulation. The study area is the Pangyo Watershed ($22.9km^2$), which includes the Unjung-Cheon and Geumto-Cheon tributaries of the Tan-Cheon stream. Simulation periods were selected from six rainfall events of a two-year period (2006-2007). For the runoff simulation, CAT was applied using three types of infiltration methods (excess rainfall, Green and Ampt and Horton). Sensitivity analysis was carried out to select the parameters and then CAT was optimized using PEST. The model performance of HEC-HMS and CAT-PEST for the rainfall events were within an acceptable limit with Nash Sutcliffe efficiencies (NSE) of 0.63-0.91 and 0.42-0.93, respectively. The simulation results of HEC-HMS have high accuracy in the case of rainfall events that have a sensitive relationship between initial soil moisture conditions and runoff characteristics. The results of CAT-PEST indicated the possibility of reflecting a real runoff system using various physical parameters.

• KIEAE Journal
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• v.11 no.2
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• pp.59-65
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• 2011

To analyze changes in the water-balance before and after using decentralized rainwater management facilities, this study carried out hydrologic modeling based on data including roof planting, rainwater use, infiltration and detention facilities applied to the sites. The results of the analysis are as follows: First, the total runoff quantity after facility installation was about 24% less than before. In particular, it showed that the surface runoff declined significantly. Second, the analysis of the effects of different decentralized rainwater management facilities revealed that the rooftop planting contributed to about a 3.5 times increase in actual evaporation than before. Third, the analysis of the effect of decentralized management facilities by different rainfall events showed that it turned to have about a 30% decreasing effect after facility installation for a monthly rainfall over 500mm or so and about 50% declining effect for a monthly rainfall about 200mm. As discussed above, the study confirmed that it is important to implement decentralized rainwater management facilities to improve inevitable changes in water-balance arising from development as it would be a significant alternative for sustainable urban development.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.592-610
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• 2020

In South Korea, the concept of water environment was expanded to include aquatic ecosystems with the Integrated Water Management implementation. Watershed-scale modeling is typically performed for hydrologic component analysis, however, there is a need to expand to include ecosystem variability such that the modeling corresponds to the social and political issues around the water environment. For this to be viable, the modeling must account for several distinct features in South Korean watersheds. The modeling must provide reasonable estimations for peak flow rate and apply to paddy areas as they represent 11% of land use area and greatly influence groundwater levels during irrigation. These facts indicate that the modeling time intervals should be sub-daily and the hydrologic model must have sufficient power to process surface flow, subsurface flow, and baseflow. Thus, the features required for watershed-scale modeling are suggested in this study by way of review of frequently used hydrologic models including: Agricultural Policy/Environmental eXtender(APEX), Catchment hydrologic cycle analysis tool(CAT), Hydrological Simulation Program-FORTRAN(HSPF), Spatio-Temporal River-basin Ecohydrology Analysis Model(STREAM), and Soil and Water Assessment Tool(SWAT).

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.276-277
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• 2005

• Proceedings of the KSEEG Conference
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• 2002.04a
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• pp.91-91
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• 2002

• Journal of Korea Water Resources Association
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• v.39 no.8 s.169
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• pp.703-716
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• 2006

The flow duration curves in the present and the ideal hydrologic cycle were derived using SWAT model. The present situation is the landuse and the groundwater withdrawal in the year of 2000 and the ideal situation is the landuse of 1975 and no groundwater withdrawal. These results were compared with the previous instream flow requirements which are the larger flow between the average drought flow and environmental control flow. As a result, the present and ideal drought flows of Ojeoncheon, Hakuicheon, Samseongcheon, and Sammakcheon, were the same and the drought flows of Samseongcheon and Sammakcheon were even zero since the baseflow is very little due to the small and mountainous watersheds. The previous instream flow requirement for the riverine function is also larger than the low flow of the ideal hydrologic cycle. The present method to set the instream flow requirement is not proper for the small mountainous watershed since it can be usually overestimated and drive the artificial measures to secure the streamflow Therefore, another method should be developed such as the low flow and the average flow between the drought flow and the low flow of the ideal hydrologic cycle using the proper hydrologic simulation model such as SWAT which can consider the landuse.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.26-36
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• 2009

Combined sewer system (CSS) has been built in the most urban areas across the nation. During dry weather conditions, CSS works fine. But during heavy rain storms, combined sewage frequently overflows into the stream. This study simulated the hydrologic cycle and pollutant loads (BOD, SS, TN and TP) in the Mokgamcheon watershed considering combined sewer overflows (CSOs). PC storm water management model (PCSWMM) was used for continuous simulation and CSOs are considered using the flow divider. Sensitivity analysis, calibration and verification for water quantity and quality are carried out. To verify CSOs, field measurements of CSOs are compared with simulated results. As a result, 41.3% of precipitation flows into the stream directly and 1.1% of water supply flows into stream as CSOs. 6.5% of BOD total loads, 12.0% of SS, 13.6% of TP, and 29.2% of TN are from CSOs. This result will be effective to the integrated watershed management for sustainability.

• KIEAE Journal
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• v.6 no.3
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• pp.27-34
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• 2006

The recent emphasis on ecological urban development has led to the need to maintain a hydrologic cycle in urban areas. As such, this study proposes decentralized rainwater management, a concept of onsite rainwater management that involves the utilization, infiltration, detention, and retention of rainwater. The main objective of this research is to estimate the proportion of decentralized rainwater management that is needed. From the research that was conducted in this study, it was found that the total runoff quantity increases by 10-20% after district lands are developed, when the probable rate of precipitation every 10 years is within this range. Thus, the runoff rate can be reduced by 10~20% of the total runoff quantity through decentralization. On the other hand, in the scale of housing complex development, the total runoff quantity increases by as much as 10~40% due to the changes in the rate of the impervious surface area. If 10-40% of the total runoff quantity was processed through decentralized rainwater management, the rate of infiltration, detention, retention, and runoff in precipitation prior to development could be recovered.

• KIEAE Journal
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• v.5 no.3
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• pp.17-24
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• 2005

Until today, rainwater management was processed without disposing the peak discharge, which was due to rainfall, to provide stability against flood damage. In this process, the natural hydrologic cycle changed quickly, and because of this, some problems that could harm human beings and the environment arose. These problems need to be addressed accordingly. One of the proposals was to carry out decentralized rainwater management through a natural hydrologic cycle on site, including utilization, infiltration, detention, and retention of rainwater. This study aims to set the direction of applicable decentralized rainwater management to housing complex in Korea. Therefore, spacial properties in urban housing complexes were analysed such as the impervious area-to-land ratio, the green area-to-land ratio, artificial land-to-land ratio etc. As the result of this study, when a housing complex was small and developed by reconstruction, the impervious area, artificial land, the green area in the artificial land-to-land ratio were high. So, direction of decentralized rainwater management of these housing complexes is available to utilize and detain rainwater. On the other hand, those of big housing complexes in land development district were low relatively. So, direction of decentralized rainwater management of these housing complexes is available to infiltrate and evaporate rainwater.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.149-153
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• 2006

Precipitation is the most important component and critical to the study of water and energy cycle. This study investigates the propagation of precipitation retrieval uncertainty in the simulation of hydrologic variables for varying spatial resolution on two different vegetation cover. We explore two remotely sensed rain retrievals (space-borne IR-only and radar rainfall) and three spatial grid resolutions. An offline Community Land Model (CLM) was forced with in situ meteorological data In turn, radar rainfall is replaced by the satellite rain estimates at coarser resolution $(0.25^{\circ},\;0.5^{\circ}\;and\;1^{\circ})$ to determine their probable impact on model predictions. Results show how uncertainty of precipitation measurement affects the spatial variability of model output in various modelling scales. The study provides some intuition on the uncertainty of hydrologic prediction via interaction between the land surface and near atmosphere fluxes in the modelling approach.