• Journal of Korean Society on Water Environment
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• v.30 no.3
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• pp.319-328
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• 2014

Dorang - the Korean term for headwater streams - occupy a large portion of the total stream length in a basin, and contribute significantly towards the quantitative and qualitative characteristics, and the ecosystem, of the main river. The Ministry of Environment of South Korea has supported the investigation of the status of Dorang in the nation's four major basins, since 2007. Without a widely accepted academic or legal definition of Dorang, however, there are limits to understand the distribution of Dorang at the national scale and to systematically compile a Dorang database. This paper, through a review of the stream classification system and Korean legal system delineating streams, defines Dorang as 1st and 2nd order streams according to the Strahler ordering method, in a 1:25,000 geographical scale. Analysis of the Geum River basin, with this definition, reveals that the total length of Dorang is 20,622.4 km (73.6% of total stream length), and the number of Dorang catchments is 23,639 (71.3% of the basin area). Further analysis of the geomorphological characteristics of Dorang catchments shows that the average total stream length is 1.1 km, average catchment length is 1.2 km, average drainage area is $0.4km^2$, and average drainage density is 3.08/km.

• Proceedings of the Korean Society of Rural Planning Conference
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• 1998.03a
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• pp.25-26
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• 1998

This study was aimed to investigate the land use characteristics between urban and rural river systems. The ecological land unit systems was used to the key method for that objectives and the visual analysis was also used. The results were as followings : The won-sung river was characterized by the formal urban river system of which the headwater was covered with the various man-made constructions. Also the pong-se river showed a little simptoms of the urbanization from the headwater that meant the urgent ecological land use evaluation about that region.

• Korean Journal of Ecology and Environment
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• v.54 no.2
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• pp.87-95
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• 2021

Macroinvertebrates in forest streams affect the overall health of other streams in the same water system. In this study, we compared differences in the benthic macroinvertebrate community at two headwater streams located at different latitudes in the southern and northern parts of South Korea. We calculated the community temperature index (CTI), which represents the thermal preferences of the benthic communities. Hierarchical cluster analyses (HCA) were conducted to compare the similarities among sampling sites. In addition, we analyzed the relationship between community composition and environmental and community characteristics using non-metric multidimensional scaling (NMDS). Our results showed that CTI was significantly different between the two regions, indicating that these benthic macroinvertebrate communities have different thermal preferences. These two regions were clearly distinguished from each other in the HCA; furthermore, seasonal differences in benthic community composition were observed within each region. The functional feeding groups present in the benthic macroinvertebrate communities were different even though their habitat was similar.

• Journal of Soil and Groundwater Environment
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• v.13 no.1
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• pp.43-51
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• 2008

Periodic fluctuation of water levels were analyzed for their causes and effects on groundwater movement. Groundwater levels were monitored from two shallow monitoring wells, G1 and G4, located at a headwater catchment in the Gwangneung Ecohydrological Research Site using pressure transducers with automatic data-loggers by five-minute interval from February to October, 2006. The water table fluctuates on a daily basis with a clear diurnal variation, and the fluctuation amplitude increases with time from the winter to the summer. Results from spectral analysis of water-level data show periodic variations in 24.38 hour and in 12.19 hour, indicating $P_1$ diurnal and $L_2$ semidiurnal tidal components, respectively. The diurnal component of the water level in summer has greater power than that in winter, implying that the water table is affected not only by earth tides, but also by evapotranspiration. Right after rain stops, the power of diurnal component of the water level decreases, indicating that evapotranspiration influences significantly diurnal periodicity. The effects of diurnal and semidiurnal components of the water level range from 0.4 to 4.2 cm and from 0.2 to 0.7 cm, respectively.

• Korean Journal of Agricultural and Forest Meteorology
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• v.9 no.2
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• pp.121-131
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• 2007

Despite the close linkage in changes between the ecological and hydrological processes in forest ecosystems, an integrative approach has not been incorporated successfully. In this study, based on the vegetation and hydrologic data of the Gwangneung headwater catchment with the Geographic Information System, we attempted such an integrated approach by employing the Regional Hydro-Ecologic Simulation System (RHESSys). To accomplish this, we have (1) constructed the input data for RHESSys, (2) developed an integrated calibration system that enables to consider both ecological and hydrological processes simultaneously, and (3) performed sensitivity analysis to estimate the optimum parameters. Our sensitivity analyses on six soil parameters that affect streamflow patterns and peak flow show that the decay parameter of horizontal saturated hydraulic conductivity $(s_1)$ and porosity decay by depth (PD) had the highest sensitivity. The optimization of these two parameters to estimate the optimum streamflow variation resulted in a prediction accuracy of 0.75 in terms of Nash-Sutcliffe efficiency (NSec). These results provide an important basis for future evaluation and mapping of the watershed-scale soil moisture and evapotranspiration in forest ecosystems of Korea.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.208-211
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• 2001

Geosynthetic Clay Liners (GCLs) have been used for the applications of the hydraulic containment system in landfill due to inexpensive costs, simple workability and distinguished ability as a barrier material. However, bentonite of GCLs is easy to be damaged by the chemical solutions. Thus, there is a need to evaluate the potential susceptibility of GCLs causing Increase the hydraulic conductivity when GCLs are exposed to raw leachate and dissolved humic substances from landfill leachate. The hydraulic conductivity tests were performed with flexible-wall permeameter (the falling -headwater/rising -tailwater procedure) in order to verify the potential susceptibility of GCLs. The values of the hydraulic conductivity conducted with raw leachate as a permeant liquid increased considerably; however, The change of the hydraulic conductivity in the case of humic and fulvic acid were not worthy of notice. As the results of swelling tests of bentonite, however, humic substances can affect badly on the dispersion behavior of bentonite. These results indicate that humic substances dissolved in leachate could reduce the hydraulic conductivity of GCLs in landfill.

• Korean Journal of Agricultural and Forest Meteorology
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• v.9 no.2
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• pp.75-87
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• 2007

Groundwater recharge rates were estimated and compared in a headwater catchment at the Gwangneung Supersite using three different methods: water-table fluctuation (WTF), mass balance, and hydrograph separation techniques. Data were obtained during the rainy season from June to September 2005. Two different WTF methods estimated the groundwater recharge rate as 25.9% and 23.6%. The mass balance calculation of chloride ions indicated recharge rates of 13.4% on average. Baseflow separation using chloride ion as a tracer from six storm hydrographs produced a 14.0% net baseflow rate on average. Because of the implicit assumption of a long-term steady state without storage change, recharge rates calculated by mass balance and hydrograph separation were smaller than those done with WTF methods, which include the amount of increased storage due to the water-level rise. Subsequently, the WTF method is superior to others in the estimation of groundwater recharge rate to comprehend the dynamic characteristics of the hydrologic cycle.

• Journal of Soil and Groundwater Environment
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• v.17 no.4
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• pp.51-62
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• 2012

Effects of climate change on groundwater system requires understanding the groundwater system in temporal and spatial scales through the long-term monitoring. In this study, the spatio-temporal variations of groundwater were analyzed through the continuous observation of water level, electrical conductivity (EC) and water temperature with automatic data-loggers and sampling in a Gwangneung catchment, Korea, for the four years from 2008 to 2011. Groundwater monitoring were performed at the nest-type wells, MW1 and MW2, located in upsteam and downstream of the catchment, respectively. During the survey period, both the total amount of annual precipitation and the frequency of concentrated rainfall have increased resulting in the elevation of runoff. Water level of MW1 showed no significant fluctuations even during the rainy season, indicating the confined groundwater system. In contrast, that of MW2 showed clear seasonal changes, indicating the unconfined system. The lag-time of temperature at both wells ranged from one to three months depending on the screened depths. Results of chemical analyses indicated that major water compositions were maintained constantly, except for the EC decreases due to the dilution effect. Values of the stable-isotope ratios for oxygen and deuterium were higher at MW2 than MW1, implying the confined system at the upstream area could be locally developed.

• Journal of Korea Water Resources Association
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• v.39 no.2 s.163
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• pp.151-160
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• 2006

In this study, threshold runoff which is a hydrologic component of flash flood guidance(FFG) is estimated by using Manning's bankfull flow and Geomorphoclimatic Instantaneous Unit Hydrograph(GcIUH) methods on Han River watershed. Geographic Information System(GIS) and 3' Digital Elevation Model database have been used to prepare the basin parameters of a very fine drainage area($1.02\~56.41km^2$), stream length and stream slope for threshold runoff computation. Also, cross-sectional data of basin and stream channel are collected for a statistical analysis of regional regression relationships and then those are used to estimate the stream parameters. The estimated threshold runoff values are ranged from 2 mm/h to 14 mm/6hr on Han River headwater basin with the 1-hour duration values are$97\%$ up to 8mm and the 6-hour values are $98\%$ up to 14mm. The sensitivity analysis shows that threshold runoff is more variative to the stream channel cross-sectional factors such as a stream slope, top width and friction slope than the drainage area. In comparisons between the computed threshold runoffs on this study area and the three other regions in the United States, the computed results on Han River watershed are reasonable.

• Journal of Korea Water Resources Association
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• v.30 no.4
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• pp.411-420
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• 1997

QUAL2E-AFOSM model is developed to forecast the water quality by reliability analysis in the Nakdong River. A varied-flow analysis is performed for the reach of Waegwan to Mulgeum to estimate hydraulic parameters. An optimization technique by BFGS method is applied to determine the optimum reaction parameters and calibrations and verifications are performed based on these parameters. A reliability analysis for the stochastic analysis in a river is studied using the AFOSM method. The variations of water quality and discharge in the headwater, tributaries, and reaction coefficients are considered. Risks of violating existing water quality standards at several loactions in the Nakdong River are computed by using the QUAL2E-AFOSM method. The computed results computed by QUAL2E-AFOSM model agree with those of the Monte-Carlo method in QUAL2EU model.