A 60-year record of rainfall from the sediments of Jinheung Pond,Jeongeup, Korea

This paper describes mean grain-size data from the ¹³⁷Cs- and ²¹⁰Pb-dated sediment core BS-3 (33-cm long) recovered from Jinheung Pond, located in the southwestern part of the Korean Peninsula. Grain-size analysis of the Jinheung Pond sediments shows a clear signal for changes in annual precipitation over the past 60 years. Instrumental records of annual precipitation (AP) and the annual summation of the precipitation of >50 mm per day (AP50), which reflects the energy available for sediment transport, correlate well with the mean grain-size distributions measured in the core. The most plausible mechanism for this response in mean grain size is variations in the annual amount and intensity of precipitation. Heavy precipitation enhances soil erosion over the catchment area and increases the transport capacity of streams and rivers. Thus, coarser mean grain size should reflect higher precipitation, and smaller mean grain size should reflect lower rainfall. In the data from core BS-3, however, grain-size peaks attributed to increased annual precipitation are not prominent. This is because a dam prevents removal of fine particles from the pond via the outflow. Therefore, the mean grain-size value represents somewhat larger sediments together with fine clays. The results of this study show that sediments of dammed lakes and ponds are well suited for high-resolution environmental investigations, especially for records of changes in precipitation over time.     

Analytical and statistical approach for evaluating the effects of a river barrage on river–aquifer interactions

The construction of a river barrage can increase groundwater levels upstream of the barrage during the rainy season. Analytical and statistical approaches were applied to evaluate the relationship between groundwater and river water at the Changnyeong–Haman river barrage in Korea using time series data of water level and electrical conductivity from June 2011 to September 2014. An artificial neural network based time series model was designed to filter out the effect of rainfall from the groundwater level data in the study area. Aquifer diffusivity and river resistance were estimated from the analytical solution of a one‐dimensional unit step response function by using the filtered groundwater level data. River resistance increased in response to groundwater level fluctuations. Cross‐correlation analyses between the groundwater and the river water showed that the lag time increased during the observation period for both the water level and the electrical conductivity while the cross‐correlation function declined for the same period. The results indicated that a constant river stage maintained at the river barrage can weaken the hydrologic stress and reduce the exchange of material between the river and the adjacent aquifer because of the deposition of fine sediment on the river bottom and walls. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrogeochemical interpretation of water seepage through a geological barrier at a reservoir boundary

A geological barrier such as a mountain ridge surrounding a large reservoir generally plays some part in preventing water leakage from the reservoir, but water flows out naturally according to the hydraulic gradient because the reservoir water level is typically higher than that outside. The hydrogeological, geochemical, and isotopic properties of water in the Daechung Dam area were analysed to characterize the source and the phenomenon of the groundwater flowing through the geological barrier. Our geochemical analysis showed that the concentrations of anions and cations tended to increase, due to the longer residence time of the water, as the distance between the sampling site and reservoir increased. Elevation differences (calculated using oxygen and hydrogen isotopes) between the highest and lowest sampling sites ranged between 350 and 420 m based on the altitude effect on isotope concentration, but the actual difference was only 35 m. These results, including analysis of the rate of water seepage from the reservoir (ca. 2.3% to 14.4% of natural recharge), indicate the possibility that groundwater in the study area originated from reservoir water that was derived from upstream water and rainfall in the high mountainous area of the upper watershed. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of analytical solution for stream depletion due to groundwater pumping in Gapcheon watershed,South Korea

A number of groundwater wells for agricultural activity, including rice farming and greenhouses, have been developed near streams over the past 20 years in South Korea. The result of a stream depletion calculation using an analytical solution of complimentary error function shows that groundwater pumping at 1949 wells drilled in the Gapcheon watershed can produce stream depletion. This amount is estimated at about 7% of annual baseflow and reaches as high as 18% of monthly baseflow during the maximum agricultural water consumption period in May. Agricultural wells have a larger effect on stream depletion than domestic wells because of their higher pumping rate. Stream depletion from agricultural wells located within 200 m from a stream represents 65% of the total depletion rate. Agricultural water policy for water use at nearby streams should be changed to reduce stream depletion and thereby maintain sustainable water development in South Korea. Copyright © 2010 John Wiley & Sons, Ltd.     

Evaluation of the impact of pyrite oxidation on rock characteristics and environment by laboratory tests

Pyrite is a common and abundant sulfidic mineral subject to oxidation. The weathering characteristics of rock-bearing pyrite sometimes impose serious influences on the surrounding environment as the oxidation of pyrite (FeS₂) generates acid drainage that results in the acceleration of rock weathering and the discharge of heavy metals into the environment. Such an accelerated weathering of rocks can reduce its mechanical properties and therefore menace the stability of rock structures, such as excavated slopes and tunnels. The evolution of physical properties of rocks and the chemical composition of drainage were evaluated in this study by a weathering test using a double Soxhlet extractor for 1 month in a laboratory setting. Three groups of biotite gneiss classified according to their pyrite content were used for the Soxhlet extraction experiment (group A with less than 0.1 wt% of pyrite; group B with about 3.3 wt% of disseminated pyrite; group C with about 5.65 wt% of vein type pyrite). The massive groups A and B had limited weathering on the surface; however, group C with the pyrite vein experienced weathering on the surface as well as along the pyrite vein. The weathering type regulated by the occurrence of pyrite apparently controlled the mechanical properties of the rock samples and the chemistry of the drainage. Groups A and B showed no significant quick absorption ratio after the 1-month experiment; however, group C had about 10 % increase in value. The uniaxial compressive strength of the three groups decreased about 20, 10 and 45 % for groups A, B and C, respectively. The mechanical properties of the samples and the chemical compositions of the drainage indicate that the oxidation of pyrite contained in the samples accelerated weathering, resulting in deterioration of mechanical properties of the rocks, and could result in the discharge of heavy metals and acid into the environment with the drainage.     

A trajectory study on the heavy snowfall phenomenon in Yeongdong Region of Korea

It is well known that when the Siberian High expands to the western part of the East Sea (Japan Sea), the distribution of snowfall amount is mainly controlled by the topography. Therefore, the maximum area of the precipitation is typically located over the slopes and near the summit of the Taebaek Mountains (called Type A). However, sometimes there were snowfall maxima near the Yeongdong coastal area of Korea rather than the neighboring mountains (called Type B) for some events. Two heavy snowfall events of 20–21 January 2008 of Type A (named by Event A) and of 13 January 2008 of Type B (named by Event B) were selected to understand the differences in the locations of snowfall maxima in the Yeongdong region of Korea. To do so, we investigated the differences between the two events in the movement of the air parcels leading to the understanding of the heavy snowfall mechanism using 3-dimensional trajectory analyses which applied the Weather Research and Forecasting (WRF) high resolution output as 3-dimensional meteorological fields. In this study, an upward motion under the influence of the northeasterly wind was observed along the slope of the mountains during Event A. In contrast, there was a strong downward motion along the slope of the mountains under the influence of the northwesterly wind while the parcels were reaching Gangneung (GN, hereafter) during the snowfall period of Event B. Furthermore, during Event B, the convergence of the parcels different in potential temperature and mixing ratio, yielded a favorable condition for forming a coastal front (discontinuity zone) around the Yeongdong coastal area. This lead to heavy snowfall over GN in the coastal plain region rather than in Daegwallyeong (DG, hereafter) near the summit of the Taebaek Mountains, which differs from the snowfall distribution of Event A.     

A review of the National Groundwater Monitoring Network in Korea

The drastic expansion of cities and the rapid economic growth in Korea have caused dramatic increases to demand from groundwater supplies for drinking, domestic, agricultural and industrial water usage. The Ministry of Construction and Transportation and the Korea Water Resources Corporation have constructed and operated the National Groundwater Monitoring Network (NGMN) throughout the country since 1995. The NGMN, an official project establishing a total of 320 groundwater monitoring stations, was completed in 2005. Each national groundwater monitoring station serves as a baseline and primary station to monitor long‐term general trends in water‐level fluctuations and in groundwater quality. The present NGMN and its monitoring capabilities were evaluated to enhance the efficiency of groundwater monitoring and to meet the new societal conditions. Based on reviews and evaluations, some suggestions and recommendations are made with regard to improvements of the national network, including the installation of rainfall gauges in groundwater monitoring stations, gathering groundwater data every hour instead of every 6 h as at present, involving major cations and anions in the regular and periodic chemical analyses, regular periodic analyses of collected groundwater data, and construction of 199 additional groundwater monitoring stations to supplement the existing groundwater monitoring network. Copyright © 2006 John Wiley & Sons, Ltd.     

Infiltration pattern in a regolith–fractured bedrock profile: field observation of a dye stain pattern

We examined the infiltration pattern of water in a regolith–bedrock profile consisting of two overburdens (OB1 and OB2), a buried rice paddy soil (PS), two texturally distinctive weathered materials (WM1 and WM2) and a fractured sedimentary rock (BR), using a Brilliant Blue FCF dye tracer. A black‐coloured coating in conducting fractures in WM1, WM2 and BR was analysed by X‐ray diffraction and scanning electron microscopy. The dye tracer penetrated to greater than 2 m depth in the profile. The macropore flow and saturated interflow were the major infiltration patterns in the profile. Macropore flow and saturated interflow were observed along fractures in WM1, WM2 and BR and at the dipping interfaces of PS–WM1, PS–WM2 and PS–BR respectively. Heterogeneous matrix flow occurred in upper overburden (OB1) and PS. Compared with OB1, the coarser textured OB2 acted as a physical barrier for vertical flow of water. The PS with low bulk density and many fine roots was another major conducting route of water in the profile. Manganese oxide and iron oxide were positively identified in the black coating material and had low crystallinity and high surface area, indicating their high reactivity with conducting contaminants. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of extractable soil manganese on oxidation capacity of different soils in Korea

We examined the relationship between soil oxidation capacity and extractable soil manganese, iron oxides, and other soil properties. The Korean soils examined in this study exhibited low to medium Cr oxidation capacities, oxidizing 0.00–0.47 mmol/kg, except for TG-4 soils, which had the highest capacity for oxidizing added Cr(III) [>1.01 mmol/kg of oxidized Cr(VI)]. TG and US soils, with high Mn contents, had relatively high oxidation capacities. The Mn amounts extracted by dithionite-citrate-bicarbonate (DCB) (Mn^d), NH₂OH·HCl (Mn^h), and hydroquinone (Mn^r) were generally very similar, except for the YS1 soils, and were well correlated. Only small proportions of either total Mn or DCB-extractable Mn were extracted by NH₂OH·HCl and hydroquinone in the YS1 soils, suggesting inclusion of NH₂OH·HCl and hydroquinone-resistant Mn oxides, because these extractants are weaker reductants than DCB. No Cr oxidation test results were closely related to total Mn concentrations, but Mn^d, Mn^h, and Mn^r showed a relatively high correlation with the Cr tests (r = 0.655–0.851; P < 0.01). The concentrations of Mn^d and Mn^h were better correlated with the Cr oxidation tests than was the Mn^r concentration, suggesting that the oxidation capacity of our soil samples can be better explained by Mn^d and Mn^h than by Mn^r. The first component in principal components analysis indicated that extractable soil Mn was a main factor controlling net Cr oxidation in the soils. Total soil Mn, Fe oxides, and the clay fraction are crucial for predicting the mobility of pollutants and heavy metals in soils. The second principal component indicated that the presence of Fe oxides in soils had a significant relationship with the clay fraction and total Mn oxide, and was also related to heavy-metal concentrations (Zn, Cd, and Cu, but not Pb).