Hydraulic analysis of a radial collector well for riverbank filtration near Nakdong River, South Korea

A radial collector well is used for the extraction of a large amount of groundwater without causing a deep drawdown at the well??s center, and it is appropriate for the supply of municipal water through riverbank filtration (RBF). Flow path changes caused by water extraction through a radial collector well were simulated to estimate the amount of river water induction at a RBF site associated with Nakdong River in South Korea. The structure of the screened horizontal arms of a radial collector well was examined with respect to effective riverbank filtration. The relative ratio of the river water induced to the radial collector well compared to the total groundwater extraction was estimated to be 27?C52%. The amount of induced river water varies with the distance of a horizontal arm from the river, indicating that the location and structure of the collector well is significant for RBF. In all simulation cases, the maximum drawdown of the groundwater level near the collector well was 2.1?m, which is not significant considering the substantial pumping rate at the study site. It was concluded that RBF radial collector wells can be used at the study site for a sustainable water supply.     

Turbidity control in downstream of the reservoir: the Nakdong River in Korea

High turbid water in the river has been one of the major concerns to the downstream residence. During heavy local rainfall, high turbid water occurs in many countries located in the Asian monsoon climate region. The Andong and the Imha reservoir, two adjacent multipurpose dams, located in the upstream of the Nakdong River in Korea have suffered from severe turbid water problem. This study applied hydrodynamic water quality model CE-Qual-Riv1 to simulate turbidity propagation in downstream coupled with long-term watershed hydrologic model SWAT to consider contributions of tributaries. The outputs of runoff and suspended sediment in tributaries are incorporated into the input data necessary for the hydrodynamic water quality model. The simulation focused on the joint dam operation to minimize the negative impact of high turbid water in downstream river. Simulated turbidity in downstream shows a good agreement with the observed data, and the approach proposed in this study is applicable for establishing a sound turbid water management in downstream of the reservoir.     

Sequential tracer tests for determining water seepage paths in a large rockfill dam, Nakdong River basin, Korea

The rockfill dam of this study has a clay core, filter zone, and sandy gravel shell, and it is located in the Nakdong River basin in Korea. Filling the reservoir began in August 1994 and it was full by April 1998. When the reservoir level was approximately 150 m, three settlement holes were found in the dam crest. To determine possible seepage paths and potential damaged areas within the rockfill dam, 15 tracer tests were performed during two periods. During the two test periods, six and nine tracer tests were conducted when the average water levels of the reservoir were 145 m and 142 m, respectively. Rhodamine WT (RWT) and bromide ion were used as tracers. For each test, 1800 to 4000 L of tracer solution were injected into the riprap for about 5 h. The 15 injection points were uniformly distributed from the right to left sides of the embankment and the two tracers were injected alternately. Tracer concentrations were monitored at 26 observation wells, which were divided into four groups by their geographical positions: right side of the crest, left side of the crest, right side of the dam toe, and left side of the dam toe. For each tracer test, more than 30 water samples were taken during a period of 96 h at each observation well. Based the breakthrough curves obtained from the sequential tracer tests, it was inferred that the most probable seepage paths and potential damaged area were in the left side of the crest (tongue wing zone) and, to a lesser extent, in the right side of the dam abutment.     

Uranium isotopes as a tracer of sources of dissolved solutes in the Han River,South Korea

The uranium (U) content and ²³⁴U/²³⁸U activity ratio were determined for water samples collected from Korea's Han River in spring, summer, and winter 2006 to provide data that might constrain the origin of U isotope fractionation in river water and the link between U isotope systematics in river waters and the lithological nature of the corresponding bedrock. The large difference in the major dissolved loads between the two major branches of the Han River, the North Han River (NHR) and South Han River (SHR), is reflected in the contrasting U content and ²³⁴U/²³⁸U activity ratio between the tributaries: low U content (0.08–0.75 nM; average, 0.34 nM) and small ²³⁴U/²³⁸U activity ratio (1.03–1.22; average, 1.09) in the NHR; and high U content (0.65–1.98 nM; average, 1.44 nM) and large ²³⁴U/²³⁸U activity ratio (1.05–1.45; average, 1.24) in the SHR. The large spatial differences in U content and ²³⁴U/²³⁸U activity ratio are closely related to both lithological differences between the two tributaries and groundwater input. The low U content and small ²³⁴U/²³⁸U activity ratio in the NHR arise mainly from a combination of surface and meteoric weathering of the dominant silicate rocks in this branch and congruent dissolution of already weathered (secular equilibrium) materials. In contrast, the high U content and large ²³⁴U/²³⁸U activity ratio in the SHR are ascribed to the dissolution of carbonates and black shales along with significant inputs of deep groundwater.     

Causality analysis of the groundwater response in a delta plain of the lower Nakdong River,Republic of Korea

The salinity of groundwater in an estuarine delta plain is sometimes related to the presence of an estuarine dam. To understand groundwater processes and salinity variation, time series data on the river water level, groundwater level, and groundwater electrical conductivity were collected for the Nakdong River in southeastern Republic of Korea. Sampling was undertaken upstream of the estuarine barrage system, which is opened and closed depending on upstream flow and seawater level. Comprehensive correlation analysis was performed between the groundwater and river water levels using bubble plots between groundwater electrical conductivity and the hydrological variables. Comparative analysis between the correlations and the field measurements of the hydrological variables indicated a negligible flux connection between the river and groundwater. Oscillatory pressure wave propagation from the river boundary explains the response patterns of the groundwater level. There were different response times for the rising and falling of the river water. Electrical conductivity in groundwater is not directly associated with that of the river except in one well close to the river boundary. The response patterns of groundwater electrical conductivity were explained by potential anthropogenic activity. Further transfer modeling results also indicate a spatial explanatory response pattern for the groundwater level. No spatial patterns in the models of electrical conductivity indicate that the hydrological processes are different with respect to the groundwater level and electrical conductivity.

     

Evaluation of the processes affecting vertical water chemistry in an alluvial aquifer of Mankyeong Watershed, Korea, using multivariate statistical analyses

Vertical variations of redox chemistry and groundwater quality were investigated in an alluvial aquifer beneath an agricultural area, in which deep groundwaters are free of NO₃, Fe, and Mn problems that are frequently encountered during the development of alluvial groundwaters. This study was performed to identify and evaluate vertical chemical processes attenuating these chemical species in the study area. For this study, the processes affecting groundwater chemistry were identified by factor analysis (FA) and the groundwater samples collected from six multilevel samplers were hierarchically classified into three different redox zones by cluster analysis (CA) based on the similarity of geochemical features. FA results indicated three major factors affecting the overall water chemistry: agricultural activities (factor 1), redox reactions (factor 2), and remnant seawater (factor 3). The groundwater quality in the study area was revealed to be controlled by a series of different redox reactions, resulting in different redox zones as a function of depth. It was also revealed that the low Fe and Mn levels in the groundwater of the deeper part are associated with sulfate reduction, which led to precipitation of Fe as iron sulfide and adsorption of Mn on it.     

Evaluation of weir construction on water quality related to algal blooms in the Nakdong River

Understanding the effect of various environmental factors on algal blooms is essential for proper management of water resources. Eight weirs were constructed on the Nakdong River in South Korea between 2010 and 2011 to manage water resources and deal with possible floods and droughts. In this study, water quality observation data were collected from eight representative monitoring sites in the Nakdong River between 2001 and 2016. Particularly, the effect of the weirs construction on water retention time was statistically analyzed in terms of algal growth and other important water quality parameters. While there was slight increase of water temperature (0.8 °C) over 16 years, the concentrations of total phosphorous (TP) and total nitrogen (TN) decreased by 62.3, and 12.9%, respectively, after the construction of weirs. This TP decrease was noticeable, but still high enough to maintain the eutrophic state of the river. Correlation statistical analysis suggests that the Chl-a concentration is positively affected by the changes of TP, TN and chemical oxygen demand. However, there was no direct correlation between Chl-a concentration and the increased water retention time from the weir construction.     

Chemical weathering of carbonates and silicates in the Han River basin,South Korea

A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO₂. The Han River drains approximately 26,000 km² and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Han River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved solids (TDS), Sr, and major ion concentrations but a higher Si concentration and ⁸⁷Sr/⁸⁶Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55 ± 11%), with a relatively small portion from carbonates (30 ± 14%), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82 ± 3%), with only 11 ± 4% from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the NHR and SHR basins, but the rate of CO₂ consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation.     

Distribution and speciation of heavy metals and their sources in Kumho River sediment,Korea

The interaction between heavy metals and river sediment is very important because river sediment is the sink for heavy metals introduced into a river and it can be a potential source of pollutants when environmental conditions change. The Kumho River, the main tributaries of the Nakdong River in Korea, can be one of the interesting research targets in this respect, because it runs through different geologic terrains with different land use characteristics in spite of its short length. Various approaches were used, including mineralogical, geochemical, and statistical analyses to investigate the distribution and behavior of heavy metals in the sediments and their sources. The effect of geological factor on the distribution of these metals was also studied. No noticeable changes in the species or relative amounts of minerals were observed by quantitative X-ray diffraction in the sediments at different stations along the river. Only illite showed a significant correlation with concentrations of heavy metals in the sediments. Based on an average heavy metal concentration (the average concentrations of Cd, Co, Cr, Cu, Ni, Pb, and Zn were 1.67, 20.9, 99.7, 125, 97.6, 149, 298 ppm, respectively), the sediments of the Kumho River were classified as heavily polluted according to EPA guidelines. The concentrations of heavy metals in the sediments were as follows: Zn > Pb > Cu > Ni > Cr > Co > Cd. In contrast, contamination levels based on the average I _geo (index of geoaccumulation) values were as follows: Pb > Cd > Zn > Cu > Co = Cr > Ni. The concentrations of heavy metals increased downstream (with the exception of Cd and Pb) and were highest near the industrial area, indicating that industrial activity is the main factor in increasing the concentrations of most heavy metals at downstream stations. Sequential extraction results, which showed increased heavy metal fractions bound to Fe/Mn oxides at the downstream stations, confirmed anthropogenic pollution. The toxicity of heavy metals such as Ni, Cu, and Zn, represented by the exchangeable fraction and the fraction bound to carbonate, also increased at the downstream stations near the industrial complexes. Statistical analysis showed that Pb and Cd, the concentrations of which were relatively high at upstream stations, were not correlated with other heavy metals, indicating other possible sources such as mining activity.     

Application of the chemometric approach to evaluate the spatial variation of water chemistry and the identification of the sources of pollution in Langat River, Malaysia

The current study presents the application of selected chemometric techniques—hierarchical cluster analysis (HCA) and principal component analysis (PCA)—to evaluate the spatial variation of the water chemistry and to classify the pollution sources in the Langat River. The HCA rendered the sampling stations into two clusters (group 1 and group 2) and identified the vulnerable stations that are under threat. Group1 (LY 1 to LY 14) is associated with seawater intrusion, while group 2 (LY 15 to LY 30) is associated with agricultural and industrial pollution. PCA analysis was applied to the water datasets for group 1 resulting in four components, which explained 85 % of the total variance while group 2 extracted six components, explaining 88 % of the variance. The components obtained from PCA indicated that seawater intrusion, agricultural and industrial pollution, and geological weathering were potential sources of pollution to the study area. This study demonstrated the usefulness of the chemometric techniques on the interpretation of large complex datasets for the effective management of water resources.     

Effect of agricultural land use on the chemistry of groundwater from basaltic aquifers, Jeju Island, South Korea

Geochemical processes were identified as controlling factors of groundwater chemistry, including chemical weathering, salinization from seawater and dry sea-salt deposition, nitrate contamination, and rainfall recharge. These geochemical processes were identified using principal component analysis of major element chemistry of groundwater from basaltic aquifers in Jeju Island, South Korea, a volcanic island with intense agricultural activities. The contribution of the geochemical processes to groundwater chemistry was quantified by a simple mass-balance approach. The geochemical effects due to seawater were considered based on Cl contributions, whereas the effects due to natural chemical weathering were based on alkalinity. Nitrogenous fertilizers, and especially the associated nitrification processes, appear to significantly affect groundwater chemistry. A strong correlation was observed between Na, Mg, Ca, SO₄ and Cl, and nitrate concentrations in groundwater. Correspondingly, the total major cations, Cl, and SO₄ in groundwater were assessed to estimate relative effect of N-fertilizer use on groundwater chemistry. Cl originates more from nitrate sources than from seawater, whereas SO₄ originates mostly from rainwater. N-fertilizer use has shown the greatest effect on groundwater chemistry, particularly when nitrate concentrations exceed 6–7 mg/L NO₃–N. Nitrate contamination significantly affects groundwater quality and 18% of groundwater samples have contamination-dominated chemistry.     

广州流溪河河水主要化学组成时空分布特征及控制因素

本次研究报道了位于广州市典型热带-亚热带河流流溪河上游、中游和下游3个站点(东星、乌石和江高)河水的主要化学成分在近1年的持续变化时间序列。结果显示,3个站点河水的阳离子均主要来自硅酸盐的化学风化输出,但贡献率略有差异,其中在上游的东星站贡献率最大,下游的江高站次之,中游的乌石站相对较少。相较之下,阴离子的来源更为多样,其中F-主要来自于岩石风化, Cl^-、SO₄^2-和NO₃^-更多地受到海洋源降雨或咸潮作用的影响。流域内主要化学风化反应以钾长石、钠长石和钙长石的溶解为主。从上游到下游, Si/TZ+*比值和Si/(Na^*+K)比值逐渐降低,说明上游硅酸盐岩风化较下游更为强烈。从上游到下游,随工农业生产活动的增加,人类活动对河流水化学组成的贡献逐渐增大,岩石风化输出的相对贡献逐渐减小。     

Characteristics and sources of atmospheric composition based on precipitation chemistry in the Shiyang River Basin,Northwestern China

Through collected precipitation samples continuously to research the precipitation chemical characteristics and the water vapor source in Shiyang River Basin, Northwestern China, a total of 121 precipitation samples had been collected in the Shiyang River Basin from July 2013 to July 2014. The results showed that, during the period of sampling, the variation range of pH value of precipitation ranged from 6.62 to 8.53 in Shiyang River Basin and the average was 7.46. The EC values ranged from 17.28 to 787.00 μs/cm, with a mean 186.66 μs/cm. Ca²⁺ and Na⁺ dominated cations and accounted for 71.80% of total cations composition, while SO₄ ^2? and NO₃ ^? dominated anions with a contribution of 82.18%. The main ionic sources are local dust aerosols and the dust from Central Asia and Northwestern China arid regions brought by the westerly, and the back trajectories also supported it. Back trajectories suggested that the air mass arrived in Shiyang River Basin mainly from the dust sources region in Central or West Asia or Northwestern China through westerly circulation in dry season, while from the Indian Ocean or the Pacific Ocean through monsoon circulation in wet season. The precipitation can be divided into three types based on the vector of water vapor transportation: the monsoon precipitation, the westerly precipitation, and the interaction precipitation (precipitation influenced both by monsoon and westerly). The type of interaction precipitation was major precipitation patterns in study area, and the westerly precipitation came next. The results are also helpful for further understanding the air pollution situation caused by dust events in study area and providing scientific basis for the effective prevention and control of atmospheric pollution.     

Sources of dissolved ions revealed by chemical and isotopic tracers in the Geum River,South Korea

Water samples were collected in the main channel of the Geum River, South Korea, and measured dissolved elemental concentrations and isotopic compositions of nitrate in order to identify the factors controlling water chemistry. Elemental concentrations significantly increased location-wise after the confluence from urban areas, indicating the changes in solute sources from chemical weathering to anthropogenic inputs such as manure, fertilizers, and sewage. In particular, the effect of sewage input is manifested in the concentrations of Cl^?, SO₄ ^2?, and Na⁺, while the NO₃ ^? concentration is influenced mainly by soil inputs with minor contributions from manure and fertilizer because both δ¹⁵N–NO₃ and δ¹⁸O–NO₃ indicate NO₃ ^? mostly consists of soil-derived nitrates in the upper reaches but manure/sewage nitrates in the lower reaches. The relative proportion of three factors, Cl^?, Ca²⁺+Mg²⁺, and NO₃ ^?, indicates that water chemistry in the upstream is controlled by the soil weathering but that in the downstream by the sewage. Seasonally, water chemistry during summer is dominated by the soil weathering due to the flushing effect but that during winter by the sewage. This study suggests that the relative proportion of three factors can be used for tracing natural and anthropogenic sources in water chemistry.     

Distribution and evolution of water chemistry in Heihe River basin

Surface- vs. ground-water chemistry in the Heihe River basin, assessed through field sampling of precipitation, surface water and groundwater, allowed geographical zones and chemical types to be differentiated. The geographical zones included: alpine ice-snow (>3,900 m), alpine meadow (3,400–3,900 m), mountain forest and shrub (2,600–3,400 m), mountain grassland (1,900–2,600 m) and desert grassland (1,500–1,900 m). Groundwater chemical types included: (1) mountain fissure and piedmont gravel, bicarbonate, (2) piedmont diluvial, alluvial and lacustrine plain, sulphate, and (3) desert salt-accumulating depression, chloride. Since the 1960s, large volumes of river water diverted for irrigation have been found to re-emerge as spring water at the edge of alluvial fans and then reintegrate the Heihe River. After a number of reuses and re-emergences in the middle reaches, the rivers level of mineralization has doubled. Hydrological changes have resulted in the marked degradation of aquatic habitats, and caused substantial, and expanding, land salinization and desertification. Solving these largely anthropogenic problems requires concerted, massive and long-term efforts.     

Natural gas sources, migration and accumulation in the shallow water area of the Panyu lower uplift: An insight into the deep water prospects of the Pearl River Mouth Basin, South China Sea

Although no drilling has been carried out in the deep water area of the Baiyun sag in the Pearl River Mouth Basin, South China Sea, the successful exploration for natural gas in the shallow water area of the Panyu lower uplift allows an insight into the prospectivity of the adjacent deep water fan system of the Baiyun sag. The Paleogene gas kitchen in the Baiyun sag provided both oil-derived gas and coal-derived gas. Fluid inclusion measurements and 2D numeric modelling of formation pressure indicate four episodes of hydrocarbon charge since the third release of the overpressure system. Seismic wipeout zones manifest several types of gas chimney which could play a role in vertical migration conduits to feed the natural gases into the deep water fan system. There would be, therefore, a low risk for hydrocarbon exploration in the deep water fan system.     

Response of groundwater chemistry to water deliveries in the lower reaches of Tarim River,Northwest China

In this paper, we analysed the monitored data from nine groundwater-monitoring transects in the lower reaches of Tarim River during the five times of stream water deliveries to the river transect where the stream flow ceased. The results showed that the groundwater depth in the lower reaches of Tarim River rose from −9.30 m before the conveyances to −8.17 and −6.50 m after the first and second conveyances, −5.81 and −6.00 m after the third and fourth the conveyance, and −4.73 m after the fifth. The horizontal extent of groundwater recharge was gradually enlarged along both sides of the channel of conveyance, i.e., from 250 m in width after the first conveyance to 1,050 m away from the channel after the fourth delivery. With the rising groundwater level, the concentrations of major anions Cl⁻, SO₄²⁻ and cations Ca²⁺, Mg²⁺, Na⁺, as well as total dissolved solids (TDS) in groundwater underwent a significant change. The spatial variations in groundwater chemistry indicated that the groundwater chemistry at the transect near Daxihaizi Reservoir changed earlier than that farther from it. In the same transect, the chemical variations were earlier in the monitoring well close to watercourse than that farther away from the stream. In general, the concentration of the major ions and TDS at each monitoring well increased remarkably when the water delivery started, and decreased with the continued water delivery, and then increased once again at the end of the study period. Hence, the whole study period may be divided into three stages: the initial stage, the intermediate stage and the later stage. According to the three stages of groundwater chemistry reaction to water delivery and the relationships between groundwater chemical properties and groundwater depths, we educe that under the situation of water delivery, the optimum groundwater depth in the lower reaches of the Tarim River should be −5 m.     

Assessment of groundwater chemistry in a coastal region (Kunsan, Korea) having complex contaminant sources: a stoichiometric approach

Groundwater chemistry in a coastal region (Kunsan, Korea) having complex contaminant sources was investigated. Water analysis data for 197 groundwater samples collected from the uniformly distributed sixty-six wells were used. Chemical analysis results indicate that groundwaters show wide concentration ranges in major inorganic ions, reflecting complex hydrochemical processes. Due to the complexity of groundwater chemistry, the samples were classified into four groups based on Cl and NO₃ concentrations and the processes controlling water chemistry were evaluated based on the reaction stoichiometry. The results explained the importance of mineral weathering, anthropogenic activities (nitrification and oxidation of organic matters), and Cl-salt inputs (seawater, deicer, NaCl, etc.) on groundwater chemistry. It was revealed that mineral dissolution is the major process controlling the water chemistry of the low Cl and NO₃ group (Group 1). Groundwaters high in NO₃ (Groups 2 and 4) are acidic in nature, and their chemistry is largely influenced by nitrification, oxidation of organic matters and mineral dissolution. In the case of chloride rich waters (Group 3), groundwater chemistry is highly influenced by mineral weathering and seawater intrusion associated with cation-exchange reactions.