• Journal of Korean Society for Geospatial Information Science
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• v.8 no.2 s.16
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• pp.11-22
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• 2000

It needs to extract the accurate topological characteristics and hydrological parameters of watershed in order to manage water resource efficiently. But, these data are processed yet by manual wok and simple operation in hydrologic fields. In this paper, we presented algorithm that could extract topological characteristics and hydrological parameters over watershed using GSIS and it gives the saving of data processing tin and the confidency of data. We presented coupling method between GSIS and hydrologic model by using extracted parameters into the input parameter of HEC-HMS hydrologic model. The extraction procedure of topological characteristics and hydrological parameters is as below. First, watershed and stream are extracted by DEM and curve unmber is extracted throughout the overlay of landuse map and soil map. Also, we extracted surface parameters like the length of the longest flow path and the slope of the longest flow path by Grid computation into watershed and stream. And we gave the method that could extract hydrologic parameters like Muskingum K and sub-basin lag tin by executing computation into surface parameters and average Sn curve number being extracted.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.520-530
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• 2021

Multivariate statistical analysis and an environmental hydrological model were applied for investigating the causes of water pollution and providing best management practices for water quality improvement in urban and agricultural watersheds. Principal component analysis (PCA) and cluster analysis (CA) for water quality time series data show that chemical oxygen demand (COD), total organic carbon (TOC), suspended solids (SS) and total phosphorus (T-P) are classified as non-point source pollutants that are highly correlated with river discharge. Total nitrogen (T-N), which has no correlation with river discharge and inverse relationship with water temperature, behaves like a point source with slow and consistent release. Biochemical oxygen demand (BOD) shows intermediate characteristics between point and non-point source pollutants. The results of the PCA and CA for the spatial water quality data indicate that the cluster 1 of the watersheds was characterized as upstream watersheds with good water quality and high proportion of forest. The cluster 3 shows however indicates the most polluted watersheds with substantial discharge of BOD and nutrients from urban sewage, agricultural and industrial activities. The cluster 2 shows intermediate characteristics between the clusters 1 and 3. The results of hydrological simulation program-Fortran (HSPF) model simulation indicated that the seasonal patterns of BOD, T-N and T-P are affected substantially by agricultural and livestock farming activities, untreated wastewater, and environmental flow. The spatial analysis on the model results indicates that the highly-populated watersheds are the prior contributors to the water quality degradation of the river.

• Journal of Korea Water Resources Association
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• v.53 no.6
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• pp.427-436
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• 2020

It is uncertain how global climate change will influence future drought characteristics over the Korean peninsula. This study aims to project the future droughts using climate change and land use change scenarios over the Korean peninsula with the land surface modeling system, i.e., Weather Research and Forecasting Model Hydrological modeling system (WRF-Hydro). The Representative Concentration Pathways (RCPs) 2.6 and 8.5 are used as future climate scenarios and the Shared Socio-economic Pathways (SSPs), specifically SSP2, is adopted for the land use scenario. The using Threshold Level Method (TLM), we identify future hydrological and ecological drought events with runoff and Net Primary Productivity (NPP), respectively, and assess drought characteristics of durations and intensities in different scenarios. Results show that the duration of drought is longer over RCP2.6-SSP2 for near future (2031-2050) and RCP8.5-SSP2 (2080-2099) for the far future for hydrological drought. On the other hand, RCP2.6-SSP2 for the far future and RCP8.5-SSP2 for the near future show longer duration for ecological drought. In addition, the drought intensities in both hydrological and ecological drought show different characteristics with the drought duration. The intensity of the hydrological droughts was greatly affected by threshold level methods and RCP2.6-SSP2 for far future shows the severest intensity. However, for ecological drought, the difference of the intensity among the threshold level is not significant and RCP2.6-SSP2 for near future and RCP2.6-SSP2 for near future show the severest intensity. This study suggests a possible future drought characteristics is in the Korea peninsula using combined climate and land use changes, which will help the community to understand and manage the future drought risks.

• Journal of Korean Society of Forest Science
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• v.85 no.4
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• pp.571-576
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• 1996

The geological and hydrological survey was carried out in Hyuseok-dong landslide area(10 ha), Youngchoon-myeon, Danyang-gun, Choongcheongbuk-do. The results showed that the bed rocks in this area consisted of shale, sandstone and limestone, and the piles of stones debris were also scattered around the hill above the study area. Soil texture was sandy loam, and bulk density of the soil in the lower part of the area was higher than that of the upper part, but void ratio of the soil in the lower part was lower than that of the upper part. Subsurface water was springing out to the surface in many places in this area. In this area, the storms over 70mm/day were frequent during the summer period from June through September. It was concluded that the occurrence of landslide had a close relationship with the geological characteristics, hydrological conditions and the rainfall distribution.

• Journal of Korea Water Resources Association
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• v.51 no.6
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• pp.471-479
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• 2018

This study analyzed the peak time of drought severity and drought period using meteorological and hydrological drought indices. Standardized Precipitation Index (SPI) using rainfall data was used for meteorological drought and Streamflow Drought Index (SDI) and Standardized Streamflow Index (SSI) using streamflow data were used for the hydrological drought. This study was applied to the Cheongmicheon watershed which is a mixture area for rural and urban regions. The rainfall data period used in this study is 32.5 years (January of 1985~June of 2017) and the corresponding streamflow was simulated using SWAT. After the drought indices were calculated using the collected data, the characteristics of drought were analyzed by time series distribution of the calculated drought indices. Based on the results of the this study, it can be seen that hydrological drought occurs after meteorological drought. The difference between SDI and SPI peak occurrence time, difference in drought start date and average drought duration is greater than SSI and SPI. In general, SSI shows more severe than SDI. Therefore, various drought indices should be used at the identification of drought characteristics.

• Journal of Korea Water Resources Association
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• v.53 no.11
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• pp.1039-1047
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• 2020

Atmospheric rivers, which transport large amount of water vapor from mid-latitude to the inland, are an important driving force of water cycle and extreme hydrologic phenomenas. The main objective of this study is to analyze the hydrological impact of the AR landfalls on the Korean Peninsula in 2000 - 2015. The result showed that the AR is closely related to the characteristics of precipitation, water level and runoff in the Korean Peninsula. The landfalls of the AR affected about 57% of annual precipitation on the Korean Peninsula, and had a greatest impact on the summer rainfall. It also affected the water level and runoff at the five major rivers of Korea, and water levels exceeding the thresholds of flood warning were observed when the AR landed. Moreover, it was found that the runoff above the third quartile with AR landfalls. These results suggest that the AR not only has a significant influence on the hydrological characteristics of the Korean Peninsula, but also have a close relationship with the extreme hydrological events like floods. The results of this study are expected to be used as the reference for the analysis of the impact of the AR on the various fields in the Korean Peninsula.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.238-238
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• 2015

There are demands for water environmental analysis of discharge processes in paddy fields, however, it is not fully understood in nutrients discharge process for watershed modeling. As hydrological processes both surface and ground water and agricultural water managements are so complex in paddy fields, the development of lowland paddy fields watershed model is more difficult than upland watershed model. In this research, the improvement of SWAT (Soil and Water Assessment Tool) model for a paddy watershed was conducted. First, modification of surface inundated process was developed in improved pot hole option. Those modification was evaluated by monitoring data. Second, the monitoring data in river and drainage channel in lowland paddy fields from 2012 to 2014 were analyzed to understand discharge characteristics. As a case study, Imbanuma basin, Japan, was chosen as typical land and water use in Asian countries. In this basin, lowland paddy fields are irrigated from river water using small pumps that were located in distribution within the watershed. Daily hydrological fluctuation was too complex to estimate. Then, to understand surface and ground water discharge characteristics in irrigation (Apr-Aug) and non-irrigation (Sep-Mar) period, the water and material balance analysis was conducted. The analysis was composed two parts, watershed and river channel blocks. As results of model simulation, output was satisfactory in NSE, but uncertainty was large. It would be coming from discharge process in return water. The river water and ground water in paddy fields were exchanged each other in 5.7% and 10.8% to river discharge in irrigation and non-irrigation periods, respectively. Through this exchange, nutrient loads were exchanged between river and paddy fields components. It suggested that discharge from paddy fields was not only responded to rainfall but dynamically related with river water table. In general, hydrological models is assumed that a discharge process is one way from watershed to river. However, in lowland paddy fields, discharge process is dynamically changed. This function of paddy fields showed that flood was mitigated and temporally held as storage in ground water. Then, it showed that water quality was changed in mitigated function in the water exchange process in lowland paddy fields. In future, it was expected that hydrological models for lowland paddy fields would be developed with this mitigation function.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3B
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• pp.161-168
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• 2012

Drought is a normal and recurrent phenomenon. But, recurring prolonged droughts have caused consequences and diverse impacts on human system. Therefore, understanding drought characteristics is indispensable element in well-prepared drought management. This study aims to investigate the hydrological droughts of Pyongchang stream and Upstream of Namhan-river in Korean peninsula. For modelling of the joint distribution of drought duration and drought severity, the copula method is used to construct the bivariate drought distribution and return period from the predetermined marginal distributions of drought duration and drought severity. As the result, the most severed drought of the Pyongchang stream and Upstream of Namhan-river occuring during period 1967 to 2007 is the 1981 and 1973. Return period for this drought derived from copula is 550 and 110 years.

• Journal of Ecology and Environment
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• v.32 no.4
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• pp.221-227
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• 2009

This study describes time lag responses between hydrological variables and phytoplankton biomass in a regulated river system, the lower Nakdong River in South Korea. The lower Nakdong is a typical flow-controlled lotic system, and its limnological characteristics are influenced by climatic variation such as monsoons and summer typhoons. Mean rainfall in the area during summer is about 1,200 mm, which comprises >60% of annual rainfall. Our results show that the regulation of flow in the Nakdong by multi-purpose dams from 1995 to 2004 affected phytoplankton dynamics. Diatom blooms occurred in winter, when the limited discharge allowed for proliferation of the phytoplankton community. Using multiple regression analysis, we detected significant time-delayed relationships between hydrological variables and phytoplankton biomass. These results may be useful for water resource managers, and suggest that 'smart flow' control would improve water quality in large regulated river systems of the Republic of Korea.

• Water Engineering Research
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• v.6 no.2
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• pp.91-99
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• 2005

One of the most important factors for estimating a flood runoff from streams is the lag time. It is well known that the lag time is affected by the morphometric properties of basin which can be expressed by catchment shape descriptors. In this paper, the notion of the geometric characteristics of an equivalent ellipse proposed by Moussa(2003) was applied for calculating the lag time of geomorphologic instantaneous unit hydrograph(GIUH) at a basin outlet. The lag time was obtained from the observed data of rainfall and runoff by using the method of moments and the procedure based on geomorphology was used for GIUH. The relationships between the basin morphometric properties and the hydrological response were discussed based on application to 3 catchments in Korea. Additionally, the shapes of equivalent ellipse were examined how they are transformed from upstream area to downstream one. As a result, the relationship between the lag time and descriptors was shown to be close, and the shape of ellipse was presented to approach a circle along the river downwards. These results may be expanded to the estimation of hydrological response of ungauged catchment.