• Journal of Korean Society on Water Environment
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• v.24 no.5
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• pp.556-562
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• 2008

We divided the downstream of South-Han River into three water zones, such as river zone, transition zone and lacustrine zone depending on the flow rate, and elucidated the major effect factors on the growth of phytoplankton and the sources of organic matters in each water zone. The difference of chlorophyll-a concentration which represents the standing crop of phytoplankton was statistically significant among the water zones. From the results of bivariate correlation analysis between chlorophyll-a concentration and water quality parameters in each water zone, the outflow of Chungju dam and hydraulic retention time of Lake Paldang which are directly related with the flow rate seemed to have obvious impact on phytoplankton growth in the downstream of South-Han River. The concentration of nutrients such as phosphorus and nitrogen exceeded the criterion of eutrophication and did not showed significant relationship with chlorophyll-a concentration. There were strong correlations between $BOD_5$ and chlorophyll-a concentrations in transition and lacustrine zone showing autochthonous production of phytoplankton was dominant source of organic matters in these zones especially in dry seasons. The results of this study show that the control of abundance of phytoplankton is the key target for reduction of the organic pollution in the downstream of South-Han River.

• Journal of Korean Society on Water Environment
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• v.20 no.6
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• pp.615-624
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• 2004

The distribution pattern of water quality parameters and phytoplankton biomass in upper inflow rivers of lake Paldang had surveyed. In North-Han river system, nutrient concentrations and algal biomass was below the standard of mesoand oligotrophy from lake Soyang to lake Paldang, maintaining good water quality, except the N5 site located near the Chuncheon-Si, showing high nutrients concentrations and algal biomass. The algal biomass of the South-Han river system showed oligotrophic level in the upstream near the lake Chungju, and increased along the flow direction showing eutrophic level in the downstream within the lake Paldang area. On the other hand, the highest concentrations of nutrients were detected in the middle stream near the Yeoju-Si and Yangpyung-Gun rather than in the downstream suggesting algal biomass in lake Paldang would not come from the upper river area but come from the growth within the lake area using nutrients from the upper inflow river.

• Journal of Korean Society on Water Environment
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• v.26 no.1
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• pp.71-80
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• 2010

We studied the nitrogen behavior and budget of Lake Paldang from March to December 2008. The particulate nitrogen (PN) concentrations ranged from 7 to 13% of the total nitrogen concentration (TN) in the stream inflows, the downstream outflow, and the lake water. The nitrate nitrogen ($NO_3-N$) concentration ranged from 67 to 78% of the TN. In the three rivers of Lake Paldang, Gyeongan River (In3 site) had the highest average of the TN, 5.037 mgN/L, but North Han River (In2 site) had the lowest average TN, 1.683 mgN/L. South Han River (In1 site) had the average TN of 2.399 mgN/L. In the dam discharge, TN showed the average 2.063 mgN/L. In the lake water, L4 site (Gyeongan River area) had the highest average TN, 3.781 mgN/L, but L3 site (North Han River) had the lowest average TN, 1.587 mgN/L. Total input of nitrogen loads to Lake Paldang was about 30,875 ton/year in 2008. Inflow rivers contributed 30,643 ton/year (South Han River: 18,111 ton/year (59%), North Han River: 11,333 ton/year (37%), and Gyeongan River: 1,199 ton/year (4%)). The atmospheric deposition had 135 ton/year, the nitrogen release from the bottom sediments had 88 ton/year, and macrophytes had 9 ton/year. Total output of nitrogen loads from Lake Paldang was about 31,256 ton/year. The downstream from dam contributed 29,877 ton/year, and the sediment deposition was 1,379 ton/year.

• Journal of Korea Water Resources Association
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• v.44 no.4
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• pp.305-314
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• 2011

Imnam Dam construction and inter-basin water transfer use by North Korea have caused several problems including water resources management aspects in the downstream reach of North Han River. Therefore, cooperative works between North and South Korea are required to make a reasonable management situation of the shared river for water quantity and quality. However, efforts by the North and the South has done not enough to achieve equitable water use in the shared river. This study analyzes main impacts caused by Imnam Dam in key sectors for reviewing water use right regarded as the most important decision-making criterion in international rivers. As the results, water deficit by Imnam Dam is calculated at 379 million $m^3$/year when river drought year for water assessment is set in 1978 in the Han River basin. Additionally hydropower production is decreased by 234 GWh/year in exclusive hydropower generation dams. In respective of water quality, BOD concentration is increased by 0.065 ppm at Sambongli in North Han River. Finally it is identified that unequitable water use based on the absolute territorial sovereignty by North Korea in North Han River has directly and indirectly affected severe impacts to South Korea as the downstream user.

• Journal of Korea Water Resources Association
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• v.34 no.2
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• pp.119-130
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• 2001

At-site and regional frequency analyses of annual maximum 1-, 2-, and 3-days rainfall in Han River basin was performed and compared based on the regional L-moments algorithm. To perform regional frequency analysis, Han River basin was subdivided into 3 sub-basins such as South Han River, North Han River, and downstream regions. For each sub-basin, the discordancy and homogeneity tests were performed. As the results of goodness of fit tests, lognormal model was selected as an appropriate probability distribution for both South Han River and downstream regions and gamma-3 model for North han River region. From Monte carlo simulation, RBIAS and RRMSE of the estimated quantiles from regional frequency analysis and at-site frequency analysis were calculated and compared each other. Regional frequency analysis shows less RRMSE of the estimated quantiles than at-sites frequency analysis in overall return periods. The differences of BRMSE between two approaches increase as the return period increases. As a result, it is shown that regional frequency analysis performs better than at-site analysis for annual maximum rainfall data in Han River basin.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.187-196
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• 1988

Meander characteristics of the Han River System using autocorrelation coefficient and variance spectrum were analysed, and meander paths were simulated by direction and direction-change series in this paper. Better wavelength estimates are obtained from direction-change spectra, dominant wavelength had the increasing tendency in order tributaries of the North Han River System, the South Han River System and the Han River Downstream System. The meander characteristics of tributaries in the North Han River, the South Han River and the Han River Downstream System could be obtained from the results of direction and direction change spectra. Direction and direction-change autocorrelograms are generally of damped oscillatory form, and wavelengths estimated from direction-change autocorrelograms correlate closely with wavelength estimated from direction-change specta.

• Journal of Korean Society on Water Environment
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• v.30 no.4
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• pp.429-440
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• 2014

This study was conducted to investigate the main cause of water quality deterioration during the spring season in the transition zone between the South Han River and the river-reservoir Paldang. A water quality model modified from QUAL2E (U.S.EPA) was used, and the model showed that eutrophication and algal production in the low flow season affected about 60% of the organic pollution at the downstream of the South Han River. This result means that phosphorus control is prior to external organic material management to ameliorate the deterioration of water quality in the water body.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.575-585
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• 1997

A daily runoff system was constructed to support decision making for water use in the downstream region of multipurpose dams in the Han River. The daily runoff system used the modified model from NWSRFS by Tabios III et al. (1986), and potential evapotranspiration was computed from Penman equation. DWOPER was used for channel routing. While the North Han River is the main river reach in the channel routing system, the South Han River and the Soyang River became tributaries. The rainfall-runoff model was calibrated and verified for five subbasins. Daily runoffs were simulated with the hydrometeorological data in 1986 and1990. The simulations were performed from April to November, and the sum of computed discharges for seven or thirty days were compared with actual releases of the downstream dams. It showed the average absolute errors of 8.7 ~31.6%. The sum of total discharges were 10% or less. While stage errors were produced by 0.5 m or less at Yoju station in the ease of simulation from April to August in 1986, the errors kept under 0.2 m since September. In the simulation for 1990, we compared two simulation results. One is produced from real internal and downstream boundary conditions and the other is one from internal and downstream boundary conditions fixed arbitrarily. The two cases showed similar results.

• Korean Journal of Ecology and Environment
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• v.41 no.4
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• pp.457-465
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• 2008

The purpose of the study was to evaluate spatial and temporal dynamics of nutrients (TN, TP), organic pollution (BOD, COD), and ionic dynamics (electrical conductivity, EC) in the North Han-River, South Han-River, and merged downriver using the dataset of $1998{\sim}2007$, obtained from the MEK (Ministry of Environment, Korea). Accord. ing to interannual nutrient analysis, TN varied slightly in the North Han-River and South Han-River, but decreased in the merged downriver along with BOD. Longitudinal analysis in the water quality showed that BOD, COD, and nutrients had linear decreasing trend along the main axis of headwater-to-downriver. Concentrations of TP and TN in the North Han-River averaged $26.97{\mu}g\;L^{-1}$, $1.696mg\;L^{-1}$, respectively, which were minimum in the three watersheds, followed by South Han-River and then the merged downriver in order. Ratios of TN:TP in the watersheds were >40 in all the sites, indicating that nitrogen may be enough for periphyton or phytoplankton growth and phosphorus may be limited partially. After the North Han-River water is merged with South Han-River, the concentrations of BOD, COD, TN, and TP were similar to the values of $S6{\sim}S7$, respectively or a little bit higher, but increased abruptly in Site M4 (Fig. 3). Thus, mean values of all the water quality parameters in the reach of $M4{\sim}M7$ sites were greater than any other sites. Seasonal data analysis indicated that BOD and EC in the downstream ($S3{\sim}S7$) was greater in the premonsoon than two seasons of the monsoon and postmonsoon, and no significant differences in BOD between the three seasons were found in the upstream ($S1{\sim}S2$). Empirical models of COD in the merged downriver was predicted ($R^2=0.87$, p>0.01, slope = 0.84, intercept = -1.28) well by EC. These results suggest that EC to be measured easily in the field may be used for estimations of nutrients and organic matter pollutions in the merged downriver and these linear models are cost-effective for the monitoring of the parameters.

• Journal of Korea Water Resources Association
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• v.44 no.4
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• pp.315-325
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• 2011

There are not many practical measures to solve a water conflict, when a hydromorphologically asymmetric situation in international rivers exists whereby downstream users may not affect upstream users but upstream users do cause downstream impacts. In taking advantage of this merit, North Korea has built Imnam Dam in upstream of North Han River and uses water for trans-basin hydropower generation. As an impact of this dam South Korean' area as a downstream user has been suffered from water deficit and dry river. It is very critical for South Korea to solve a key problem such as water allocation for water supply and river maintenance. Therefore, this study is aim to suggest alternatives for equitable water allocation in consideration of special circumstances between the South and the North. For this, reviewing the allocation methods of water rights is carried using lessons obtained from international river cases. The results show that the minimum desired streamflow is calculated at 7.3 $m^3/sec$; water budget analysis by the equitable distribution of streamflows at the border line of the North Han River, the difference in water supply deficiency is at 3.7 $m^3/sec$ before and after Imnam Dam; in the determined distribution method, the difference in water deficiency is at 11.38 $m^3/sec$. These results show that South Korea should be secured 11.38 $m^3/sec$ from North Korean's Imnam Dam in respective of water use right and sound river maintenance.