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During the cold dry season, a large amount of groundwater is pumped for water-curtain cultivation in agricultural fields mostly located near the four major rivers of South Korea. Several weirs, installed previously to secure sufficient water resources from these rivers, were opened in 2017 for restoring the riverine environment. Weir-controlled river level fluctuations have altered stream–aquifer interactions, leading to groundwater drawdown. In this study, changes in stream–aquifer interaction caused by seasonal pumping and weir opening were investigated, using Visual MODFLOW. Two indexes that considered the pump type and aquifer characteristics—the pumping available thickness (PAT) and aquifer productivity index (API)—were used to analyze the effects of weir opening on seasonal groundwater use. Our simulations indicated that weir opening had a large impact on seasonal groundwater use due to groundwater drawdown, especially with respect to centrifugal pumps located in low transmissivity areas where the API decreased after the weir was opened. The resulting decrease in groundwater pumping rates would lower the thermal effect of the water-curtain greenhouse process. This indicates that water supply alternatives are needed so that the weirs can be operated efficiently and field requirements can be met, while the deleterious effects on groundwater are avoided.

The Juksan weir, installed in the Yeongsan river in South Korea from 2010 to 2012, has secured sustainable water resources and helped control flooding. However, low river flow velocities due to the weir have deteriorated the quality of the river water. For natural river restoration, the water gate was opened in 2017. In this study, the three-dimensional finite difference model Visual MODFLOW was used to analyze the effects of gate opening on stream–aquifer interactions. A conceptual model was developed to simulate the stream–aquifer dynamics caused by the operation of the water gate at the Juksan weir. Groundwater data were also analyzed to determine the impacts of weir operations on groundwater quality. Our results indicate that a lower river level due to the weir opening changed the groundwater flow, which then affected the water balance. The change in groundwater flow increased the variability of the groundwater quality which had homogenized because of induced recharge after the construction of the weir. This could affect groundwater use in agricultural areas near the weir. Therefore, further groundwater monitoring and hydrodynamic analyses are required to anticipate and address any potential issues.

Hydraulic structures have a significant impact on riverine environment, leading to changes in stream&ndash, aquifer interactions. In South Korea, 16 weirs were constructed in four major rivers, in 2012, to secure sufficient water resources, and some weirs operated periodically for natural ecosystem recovery from 2017. The changed groundwater flow system due to weir operation affected the groundwater level and quality, which also affected groundwater use. In this study, we analyzed the changes in the groundwater flow system near the Geum River during the Baekje weir operation using Visual MODFLOW Classic. Groundwater data from 34 observational wells were evaluated to analyze the impact of weir operation on stream&ndash, aquifer interactions. Accordingly, the groundwater discharge rates increased from 0.23 to 0.45 cm/day following the decrease in river levels owing to weir opening, while the hydrological condition changed from gaining to losing streams following weir closure. The variation in groundwater flow affected the groundwater quality during weir operation, changing the groundwater temperature and electrical conductivity (EC). Our results suggest that stream&ndash, aquifer interactions are significantly affected by weir operation, consequently, these repeated phenomena could influence the groundwater quality and groundwater use.

In South Korea, a significant amount of groundwater is used for the heating of water-curtain insulated greenhouses during the winter dry season, which had led to problems of groundwater depletion. A managed aquifer recharge (MAR) project is currently underway with the goal of preventing such groundwater depletion in a typical cultivation area, located on an alluvial aquifer near the Nam River. In the present study, FEFLOW, a three-dimensional finite element model, was used to evaluate different strategies for MAR of the cultivation areas. A conceptual model was developed to simulate the stream-aquifer dynamics under the influence of seasonal groundwater pumping and MAR. The optimal rates and duration of MAR were assessed by analyzing the recovery of the groundwater levels and the change in the groundwater temperature. The simulation results indicate that a MAR rate of 8000 m3 /d effectively restores the groundwater level when the injection wells are located inside the groundwater depletion area. It is also demonstrated that starting the MAR before the beginning of the seasonal pumping is more effective. Riverbank filtration is preferable for securing the injection water owing to plentiful source of induced recharge from the river. Locating the pumping wells adjacent to the river where there are thick permeable layers could be a good strategy for minimizing decreases in the groundwater level and temperature.

Large agricultural fields in South Korea are located mostly on alluvial plains, where a significant amount of groundwater is used for heating of water-curtain insulated greenhouses. Such greenhouses are commonly used for crop cultivation during the winter dry season from November to March. After use the groundwater is discharged directly into streams, causing groundwater depletion. A hydrogeological study was carried out in a typical agricultural area of this type, located on an alluvial aquifer near the Nakdong River. Groundwater levels, chemical characteristics, and temperatures from 68 observation wells were analyzed to determine the impacts of seasonal groundwater pumping on the groundwater system and stream-aquifer interactions. Our results show that the groundwater system has not yet reached a state of dynamic equilibrium. Decades of excessive seasonal pumping have caused a gradual decline of groundwater levels, leading to groundwater depletion, especially in areas further from the river. Seasonal pumping has also significantly affected groundwater quality in the aquifer near the river. Groundwater temperature is decreasing (in this case a disadvantage), and saline groundwater is being diluted by induced recharge. The results of this study provide a basic outline for effective integrated water management that is widely applicable in South Korea.

Visual MODFLOW was used for quantifying stream-aquifer interactions caused by seasonal groundwater pumping. Ahypothetical conceptual model was assumed to represent a stream-aquifer system commonly found in Korea. The modelconsidered a two-layered aquifer with the upper alluvium and the lower bedrock and a stream showing seasonal waterlevel fluctuations. Our results show that seasonal variation of the stream depletion rate (SDR) as well as the groundwaterdepletion depends on the stream depletion factor (SDF), which is determined by aquifer parameters and the distance fromthe pumping well to the stream. For pumping wells with large SDF, groundwater was considerably depleted for a longtime of years and the streamflow decreased throughout the whole year. The impacts of return flow were also examined byrecalculating SDR with an assumed ratio of immediate irrigation return flow to the stream. Return flow over 50% ofpumping rate could increase the streamflow during the period of seasonal pumping. The model also showed that SDR wasaffected by both the conductance between the aquifer and the stream bed and screen depths of the pumping well. Ourresults can be used for preliminary assessment of water budget analysis aimed to plan an integrated management of waterresources in riparian areas threatened by heavy pumping.Key words: Stream Depletion Rate (SDR), Stream Depletion Factor (SDF), Stream-aquifer interaction, Seasonal pump-ing, Visual MODFLOW

The "Four Major Rivers Restoration Project" was conducted to secure sufficient water resources, introduce comprehensive flood control measures, improve water quality, and restore river ecosystems in Korea. As a part of the project, 16 sites were dredged and weirs were installed in the Han, Geum, Yeongsan, and Nakdong Rivers from late 2010 to early 2012. Groundwater data were obtained from 213 groundwater monitoring wells near the four major rivers to analyze the impacts of weir construction on the nearby groundwater flow system. The groundwater level and chemical characteristics were analyzed to investigate how the groundwater flow system and water quality changed following weir construction. Our results show that the groundwater level immediately increased with increased river levels following weir construction. In addition, the hydrologic condition of some rivers upstream of the weirs was changed from gaining to losing streams. Consequently, the direction of groundwater flow changed from perpendicular to parallel to the river, and groundwater downstream of the weir became recharged from the area upstream of the weir. This should affect groundwater quality, which should become similar to the river water; however, this change has not yet been observed. Therefore, both further monitoring of the groundwater quality and further hydrogeochemical analysis are required for quantitative evaluation of the effects of weir construction in the study area.

Korea Institute of Geoscience and Mineral ResourcesReceived 14 February 2015; received in revised form 7 March 2015; accepted 11 March 2015선형 또는 군집형으로 배치된 양수정 배열 조건에서 최적의 복수 주입정 위치를 결정하는 최적화 프로그램을 개발하였다. 다양한 목적함수를 제시하였으며 담금질모사 기법을 이용하여 목적함수를 만족시키는 주입정의 최적 위치를 평가하였다. 주입수의 회수율의 최대화를 목적함수로 설정할 경우, 우물 배열에 관계없이 두 개의 주입정을 모두 우물 군집내부에 설치하는 것이 가장 효율적인 것으로 나타났다. 회수율의 최대화와 동시에 기존 양수정의 양수량을 고르게 증가시키는 통합목적함수를 고려하여 두 개의 주입정을 설치할 경우, 우물 배열에 관계없이 우물 배열의 양측면부가 주입정위치로 적합한 것으로 분석되었다. 주입정 위치 최적화를 위한 다수의 시나리오 분석 결과, 최적의 결과에 근접하는 지역적 최솟값 또는 최댓값이 다수 존재하는 것으로 나타났으며, 이는 주입정의 최적 위치를 현장의 조건에 맞게 선택적으로 결정할 수 있는 개연성이 존재하는 것을 의미한다. 결론적으로, 본 연구는 담금질모사 기법이 다양한 목적함수에부합하는 복수 주입정의 최적 위치 평가에 성공적으로 이용될 수 있음을 보여 주었다.주요어 : 담금질모사 , 최적화, 지하수흐름모델 , 인공함양 , 주입정A FORTRAN program was developed to determine the optimal locations of multiple recharge wells in an aqui-fer with different arrangements of pumping wells. The simulated annealing algorithm was used to find optimallocations of two recharge wells which satisfied three objective functions. The model results show that locating twoinjection wells inside the cluster of pumping wells is efficient if the recovery rate only was taken into account. Incontrast, placing injection wells to the side of the cluster is desirable if the simulation considers aggregate objec-tive function. Therefore, installing an injection well on each side of the cluster seems to yield the maximum recov-ery rates for the existing pumping wells, and it yields similar increases in pumping rate for all wells in the cluster.The locations of recharge wells can be arranged in numerous configurations, because there are multiple near-opti-mal local minima or maxima. These results indicate that the simulated annealing can yield effective evaluations ofthe optimal locations of multiple recharge wells. In addition, the suggested aggregate objective function can be uti-lized as an appropriate multi-objective optimization.Key words: simulated annealing, optimization, groundwater flow model, artificial recharge, injection well

An artificial recharge test aimed at investigating transport characteristics of the injected water plume in a fractured rock aquifer was conducted. The test used an injection well for injecting tap water whose temperature and electrical conductivity were different from the groundwater. Temporal and depth-wise variation of temperature and electrical conductivity was monitored in both the injection well and a nearby observation well. A highly permeable fracture zone acting as the major pathway of groundwater flow was distinctively revealed in the monitoring data. A finite element subsurface flow and transport simulator (FEFLOW) was used to investigate sensitivity of the transport process to associated aquifer parameters. Simulated results showed that aperture thickness of the fracture and the hydraulic gradient of groundwater highly affected spatio-temporal variation of temperature and electrical conductivity of the injected water plume. The study suggests that artificial recharge of colder water in a fractured rock aquifer could create a thermal plume persistent over a long period of time depending on hydro-thermal properties of the aquifer as well as the amount of injected water.

Thermal and physical properties were measured on 206 Jurassic granite samples obtained from three boreholes in the central part of Korea. Thermal conductivity(λ), thermal diffusivity(α), and specific heat(Cp) were measured in a laboratory; the average values are λ=2.813 W/mK, α=1.296 mm 2 /sec, and Cp=0.816 J/gK, respectively. In addition, porosity(φ), and dry and saturated density(ρ) were measured in the laboratory; the average values are φ=0.01, ρ(dry)=2.662 g/cm 3 and ρ(saturated)=2.67 g/cm 3 , respectively. Thermal diffusivity of 10 granite samples were measured with increasing temperature from 25°C to 200°C. In this study, we found that thermal diffusivity at 200°C is about 30% lower than thermal diffusivity at 25°C. In correlation analysis, thermal conductivity increases with increasing thermal diffusivity. However, thermal conductivity does not show good correlation with porosity and density. Consequently, we know that thermal conductivity of granite would be more influenced by mineral composition than by porosity. We also derived ρ = �2.393 × φ + 2.705 from density and porosity data. XRD and XRF analysis were performed to investigate effects of mineral and chemical composition on thermal conductivity. From those results, we found that thermal conductivity increases with increasing quartz and SiO2, and decreases with increasing albite and Al2O3. Regression analysis using those mineral and chemical composition were carried out ; we found K = 0.0294VQuartz +1 .93 for quartz, K = 0.237WSiO2 � 14.09 for SiO2, and K = 0.053WSiO2 � 0.476WAl2O3 +6 .52 for SiO2 and Al2O3. Specific gravities were measured on 10 granite samples in the laboratory. The measured specific gravity depends on chemical compositions of granite. Therefore, specific gravity can be estimated by the felsic-mafic index(F) that is calculated from chemical composition. The estimated specific gravity ranges from 2.643 to 2.658. The average relative error between measured and estimated specific gravities is 0.677%.

Temporal variation of groundwater levels in Jeju Island reveals time-delaying and dispersive process of recharge, mainly caused by the hydrogeological feature that thickness of the unsaturated zone is highly variable. Most groundwater flow models have limitations on delineating temporal variation of recharge, although it is a major component of the groundwater flow system. A new mathematical model was developed to generate time series of recharge from precipitation data. The model uses a convolution technique to simulate the time-delaying and dispersive process of recharge. The vertical velocity and the dispersivity are two parameters determining the time series of recharge for a given thickness of the unsaturated zone. The model determines two parameters by correlating the generated recharge time series with measured groundwater levels. The model was applied to observation wells of Jeju Island, and revealed distinctive variations of recharge depending on location of wells. The suggested model demonstrated capability of the convolution method in dealing with recharge undergoing the time-delaying and dispersive process. Therefore, it can be used in many groundwater flow models for generating a time series of recharge.

Radon (222Rn) and uranium (U) measurements were conducted in 98 groundwater samples in Yongin area, Korea to identify the factors controlling their levels and spatial distributions. Groundwater samples were obtained from the different depth of wells used for drinking water and irrigation. 222Rn and U concentrations were measured using a liquid scintillation counter (LSC) equipped with a pulse-shape analyzer and inductively coupled plasma mass spectrometers (ICP-MS), respectively. Large variations were observed in groundwater concentrations of 222Rn and U, ranging between 0.6 &plusmn, 0.1&ndash, 673.7 &plusmn, 8.7 Bq L&minus, 1 and 0.02&ndash, 117.00 &micro, g L&minus, 1, respectively. Correlation analysis revealed no significant relationship between field parameters (temperature, electrical conductivity, pH, and dissolved oxygen) and 222Rn or U concentrations. The fact that 222Rn and U concentrations were higher in granite areas than gneiss areas suggests that lithology plays a significant role in controlling the levels and spatial distributions of the two radionuclides. Furthermore, groundwater 222Rn and U behaviors have been affected by the existence of fault and well depth. Especially, the temporal monitoring of 222Rn suggests that 222Rn concentrations in the shallow groundwater may be controlled by variation in rainfall and artificial effects such as water curtain cultivation conducted in the winter season in this study area.

Groundwater is a major source of water use in Jeju volcanic island of Korea. Due to highly permeable surface conditions, the island does not have any perennial streams or rivers. Therefore, accurate estimation of groundwater recharge and understanding groundwater system are critical to make a reliable water budget in the island. A distributed quasi steady state water balance model, WetSpass (Water and Energy Transfer between Soil, Plants and Atmosphere under quasi Steady State) was adopted to estimate spatially-varying groundwater recharge considering soil type, land use, topography, and groundwater depth. The results from the study using weather data from October 2006 to September 2007 indicated that the eastern and northern parts of the island showed relatively higher rate of recharge as compared with the western region. A total of 69% of recharge occurred in the middle of the Island where topographic elevation is greater than 200 m from the mean sea level. The total amount of recharge was 1,935.6 million tons, 41.8% of the total precipitation. The higher rate of recharge was observed in the watersheds where forest and bare soil as land uses, and sandy loam and clay loam as soil types are dominant. The total runoff was 1,142.7 million tons (24.7%) and the total evapotranspiration was 1,555.7 million tons (33.5%). The zonal hydraulic conductivities estimated with groundwater flow modeling and parameter estimation process showed a wide range of values from 1.2 m/d to 5,380 m/d. The results of groundwater flow modeling indicated that the crest of groundwater table is off-centered from the peak of Mt. Halla toward south.

The water-table fluctuation (WTF) method has been often used for estimating groundwater recharge by analysis of waterlevel measurements in observation wells. An important assumption inherent in the method is that the water level rise is solely caused by precipitation recharge. For the observation wells located near a stream, however, the water-level can be highly affected by the stream level fluctuations as well as precipitation recharge. Therefore, in applying the WTF method, there should be consideration regarding the effect of stream-aquifer interactions. Analysis of water-level hydrographs from the National Groundwater Monitoring Wells of Korea showed that they could be classified into three different types depending on their responses to either precipitation recharge or stream level fluctuations. A simple groundwater flow model was used to analyze the errors of the WTF method, which were associated with stream-aquifer interactions. Not surprisingly, the model showed that the WTF method could greatly overestimate recharge, when it was used for the observation wells of which the water-level was affected by streams. Therefore, in Korea, where most groundwater hydrographs are acquired from wells nearby a stream, more caution is demanded in applying the WTF method.

Summary A simple hydrologic feedback model has been developed to simulate daily responses of hydrologic processes including interception, runoff, evapotranspiration, infiltration, and recharge under various conditions of vegetation, land cover, and soil in a fully-distributed manner. The daily soil water balance is a key element to link surface and subsurface models as it calculates infiltration and groundwater recharge by considering a time delay routing through a vadose zone down to the groundwater table. MODFLOW is adopted to simulate groundwater flow and interaction with surface water components as well. The model also can easily be localized by simple modification of soil and crop properties. The actual application of the model for a watershed in the Geum River Basin in Korea showed reliable hydrologic feedbacks between the surface and subsurface hydrologic systems.

For the Hancheon drainage area in Jeju island, a groundwater flow model using Visual MODFLOW was developed to simulate artificial recharge through injection wells installed in the Hancheon reservoir. The model was used to analyze changes of the groundwater level and the water budget due to the artificial recharge. The model assumed that of storm water would recharge annually through the injection wells during the rainy season. The transient simulation results showed that the water level rose by 39.6 m at the nearest monitoring well and by 0.26 m at the well located 7 km downstream from the injection wells demonstrating a large extent of the affected area by the artificial recharge. It also shown that, at the time when the recharge ended in the 5th year, the water level increased by 81 m at the artificial reservoir and the radius of influence was about 2.1 km downstream toward the coast. The residence time of recharged groundwater was estimated to be no less than 5 years. The model also illustrated that 15 years of artificial recharge could increase the average linear velocity of groundwater up to 1540 m/yr, which showed 100 m/yr higher than before. Increase of groundwater storage due to artificial recharge was calculated to be and at the end of the 5th and 10th years of artificial recharge, respectively. The rate of storage increase was gradually diminished afterwards, and storage increase of was retained after 15 years of artificial recharge. Conclusively, the artificial recharge system could augment of additional groundwater resources in the Hancheon area.

Based on Maxwell-Eucken(ME) model, which is one of structural models, a new model for predicting the effective thermal conductivity of variably saturated porous materials is proposed. The new model is a linear combination of three ME models having matrix, water, and air as a continuous phase. The coefficient of the corresponding linear equation is defined by a parameter referred to as 'the continuity coefficient', which provides a relative degree of continuity of each phase. The continuity coefficient of matrix is assumed to be linearly proportional to porosity. The model can be linear or nonlinear depending on how the continuity coefficients of water and air vary with water saturation. The feasibility of the proposed model was examined by both numerical and experimental results. Both linear and nonlinear models showed a high accuracy of prediction with R2 values of 0.86-0.98 and 0.88-0.99, respectively. The numerical and experimental results also showed that the continuity coefficient of matrix was linearly proportional to porosity. Therefore, the proposed prediction model can be effectively used to estimate effective thermal conductivity of unsaturated porous materials by measuring porosity, water content and mineralogical compositions of matrix.

For 21 rock samples consisting of granite, sandstone and the effective thermal conductivity (TC) was measured with the LFA-447 Nanoflash, and mineralogical compositions were also determined from XRD analysis. The structural models were used to examine the effects of quartz content and the size of minerals on TC of rocks. The experimental results showed that TC of rocks was strongly related to quartz content with value of 0.75. Therefore, the proposed regression model can be a useful tool for an approximate estimation of TC only from quartz content. Some samples with similar values of quartz content, however, illustrated great differences in TC, presumably caused by differences in the size of minerals. An analysis from structural models showed that TC of rocks with fine-grained minerals was likely to fall in the region between Series and EMT model, and it moved up to ME and Parallel model as the size of minerals increased. This progressive change of structural models implies that change of TC depending on the size of minerals is possibly related to the scale of experiments; TC was measured from a disk sample with a thickness of 3 mm. Therefore, in case of measurements with a thin sample, TC can be overestimated as compared to the real value in the field scale. The experimental data illustrated that the scale effect was more pronounced for rocks with bigger size of minerals. Thus, it is worthwhile to remember that using a measured TC as a representative value for the real field can be misleading when applied to many geothermal problems.

The major Mo deposits in South Korea were formed during the Jurassic Daebo orogeny, the Late Cretaceous and the Tertiary post-orogenic igneous activities, and are characterized by a variety of genetic types such as pegmatite, greisen, skarn, porphyry and vein types. The Jangsu mine is a pegmatite-style deposit which is genetically related to the Jurassic ilmenite-series two-mica granite with the Mo mineralization age of Ma. The Geumseong mine occurs as a skarn/porphyry-style deposit associated with highly fractionated granite. Its age of Mo mineralization within aplitic cupola is about 96.5~l07.5 Ma. The Yeonil mine is a porphyry-style deposit, and the Geumeum mine is a veinlet-style deposit along the fracture zone with their mineralization ages of and Ma, respectively. The contrasts in the style of Mo mineralization in Korea reflect the different environment of the related magmatism. The Jurassic mineralization, being related to deep-seated granitoids, occurs as a pegmatite-style deposit, whereas the Cretaceous one, being related to subvolcanic granitoids, occurs as skarn/porphyry/vein-type ore deposits. The Tertiary Mo mineralization has a close relationship with the igneous activities associated with the Tertiary basin formation along the east coast, Korean peninsular.

The performance of the ATES (aquifer thermal energy storage) system primarily depends on the thermal interference between warm and cold thermal energy stored in an aquifer. Additionally the thermal interference is mainly affected by the borehole distance, the hydraulic conductivity, and the pumping/injection rate. Thermo-hydraulic modeling was performed to identify the thermal interference by three parameters and to estimate the system performance change by the thermal interference. Modeling results indicate that the thermal interference grows as the borehole distance decreases, as the hydraulic conductivity increases, and as the pumping/injection rate increases. The system performance analysis indicates that if η (the ratio of the length of the thermal front to the distance between two boreholes) is lower than unity, the system performance is not significantly affected, but if η is equal to unity, the system performance falls up to ∼22%. Long term modeling for a factory in Anseong was conducted to test the applicability of the ATES system. When the pumping/injection rate is 100 m3/day, system performances during the summer and winter after 3 years of operation are estimated to be ∼125 kW and ∼110 kW, respectively. Therefore, 100 m3/day of the pumping/injection rate satisfies the energy requirements (∼70 kW) for the factory.

Two different time series data sets, shallow ground temperatures of 58 synoptic stations of the Korea Meteorological Administration (KMA) and groundwater temperatures of 67 wells of the National Groundwater Monitoring Network (NGMN), were analyzed to estimate the apparent thermal diffusivity by using the analytical solution of the one-dimensional heat conduction equation. The KMA temperature data measured at 1–5 m depths illustrated values of the phase delay and the amplitude decay coincident with their theoretical relationship, indicating that the conductive heat transport should prevail over the nonconductive processes. On the contrary, some of the estimates from temperatures at a depth of 0.5 m were away from the theoretical values. It is most likely that the deviation would be caused by the effects of latent heat associated with freezing and thawing of the near ground surface. In contrast to KMA data, results obtained from the NGMN data highly deviated from the theoretical ones, and thereafter yielded unacceptably high values of thermal diffusivities as compared to the representative values of soils and rocks. Implication of the discrepancy between two data sets was discussed in conjunction with perturbation of the conductive heat transport by free convection of water and air occurring in large diameter wells as well as the convective heat transport by groundwater flow.

The rainfall of Korea in the summer monsoon period occupies more than 50% of the annual precipitation in most areas, and thus groundwater recharge to shallow aquifers is dominantly controlled by the amount and the pattern of monsoon precipitation. This paper presents two numerical models that demonstrate linear relationships between precipitation and recharge. First, a simple heat transport model employing a lumped parameter approach is presented for estimating two lumped parameters related to water flux and thermal diffusivity in the vadose zone. The model determines the parameters by a simple optimization process that minimizes the root-mean-square error between simulated and measured temperatures. The model is applied to 22-year time series data of soil temperatures measured at a synoptic station of Korea. The impact of monsoon precipitation on the thermal regime is clearly reflected in the simulated results by illustrating a linear relationship between precipitation and the water flux in the vadose zone. Secondly, an infiltration model is presented for analyzing variability of precipitation recharge in relation to the monsoon rainfall. The model simulates the unsaturated flow from time series data of precipitation and pan evaporation, assuming immediate removal of surface ponding, a linear relationship between the evaporation rate and the soil water content, and a static water table. Numerical simulations were performed for three soil textural groups by using 20-year meteorological data. The results demonstrate that the annual recharge is linearly proportional to the annual precipitation with varying degrees of the correlation coefficient depending on soil types. Sensitivity analyses show that the uncertainties in evaporation-related model parameters significantly affect the model results with controlling tradeoff between recharge and evaporation estimates.

A distributed numerical model utilizing MacCormack finite difference method is developed to simulate the transient subsurface temperature profiles under time varying groundwater recharge. It is not restricted to constant percolation rate and sinusoidal temperature variations as is the case in most models. The model is validated with the data available for the Nagaoka plain, Japan showing good agreement for the computed subsurface temperatures having correlation coefficient (asR 2 ) and root mean square error (RMSE) as 0.89 and 0.42, respectively. The model is employed to investigate the alteration in the subsurface thermal regime due to variable recharge resulting from precipitation in South Korea. Results reveal that the subsurface thermal regime is influenced significantly by the temporal variability in groundwater recharge and temperature at the surface, and subsurface temperatures are not necessarily sinusoidal at all depths. Seasonal variations and the effect of short term hydrological phenomena are clearly depicted in simulated results. The temporal variations of the subsurface temperature are highly nonlinear near the ground surface and become almost linear beyond 10 m. The subsurface temperature profiles vary significantly from one cycle to other and tend to be vertical beyond 15 m. Its variability also depends upon the Peclet number.

A simple numerical model is presented for estimating vertical groundwater flux from transient subsurface temperature profiles obtained from field measurements. The model developed utilizes the MacCormack scheme, which is based on the Finite Difference Method (FDM), for solving the governing partial differential equation of convection–diffusion heat transport with appropriate initial and boundary conditions within the subsurface. In order to validate the model, numerical solutions obtained for the study area located in the Nagoka plain, Japan are compared with the published measured data and results obtained by others. Results obtained show good agreement and fit the observed data with a correlation coefficient, R2, of 0·88. The estimated groundwater flux is 1·85 × 10−7 m s−1. Sensitivity analyses were also carried out to investigate the effect of variations in groundwater fluxes, thermal properties and the annual thermal variability due to climatic changes on the transient subsurface temperature profiles and to have a better understanding of the subsurface thermal dynamics. A substantial effect of annual climatic variability is observed on the temporal distributions of temperature depth profiles, and a better estimate of thermal parameters is required to estimate vertical groundwater flux. The largest change in subsurface temperature depth profiles due to groundwater flux over a year is within ± 4 °C. The influence of groundwater flux on subsurface temperature distributions in space and time may be more pronounced in areas where the top of the saturated layer fluctuates considerably. Variation in thermal diffusivity results in temperature change up to ± 1·5% and may cause change in groundwater flux estimate by ± 18%. The model presented has merits over analytical solutions (type curve matching techniques) in terms of suitability and applicability to real field problems, and can be a good asset to hydrological models as quantifying groundwater recharge or deducing it from other quantities, such as rainfall, evapotranspiration and runoff, is often complicated. Copyright © 2007 John Wiley & Sons, Ltd.

A geochemical study was carried out in a small spa area (Onyang Spa, Korea) where intensive pumping of deep thermal groundwater (1 300 000 m3 year−1) is taking place. This has caused the deep fractures to lose their artesian pressure and the upper shallow fractures have been encroached by shallow, cold waters. To quantify the influence of long-term heavy pumping on the quality of the geothermal water, groundwater sampling and chemical analysis, water-level measurement, and well loggings were performed for the selected deep thermal wells and shallow cold wells. Chemical analysis results indicate a big contrast in water chemistry and origins between the two water types. Shallow groundwater shows a wider concentration ranges in solutes that are closely related to human activity, illustrating the water's vulnerability to contamination near the land surface. Plots of water chemistry as a function of fluoride reveal that the quality of the thermal water was greatly influenced by the shallow, cold groundwater and that intensive pumping of the deep thermal groundwater has caused the introduction of shallow groundwater into the deeper fractures. Although the deep and the shallow fractures were piezometrically separated to some extent, a mixing model based on fluoride and nitrate indicated that the cold-water fractions in the thermal wells are up to 50%. This suggests that the thermal water is faced with water quality degradation by the downward flow of the shallow, cold water. Restriction on the total of all the pumpage permits per unit area is suggested to restore the artesian pressure of the deep thermal aquifer and to prevent cold-water intrusion in the study area. Copyright © 2004 John Wiley & Sons, Ltd.

In order to consider a counterplan to preserve an ancient royal tomb in Kongju, Korea, the deformation of the wall structure, the atmospheric temperature in the tomb, and the groundwater level have been monitored. The long-term measurement of biaxial tilting of the tomb walls revealed that the brick-built subsurface opening had been subjected to severe structural instability. The measured deformation of the tomb was consistent with the displacement of soil around the tomb calculated using a numerical analysis. The instability of the tomb structure is closely related to the rainy season as the deformations measured are several times that in the dry season. A sudden change of temperature inside the tomb exerted an influence on the deformation of the tomb structure as well. It is suggested that the excavation be restored for tourists, the quicklime layer for preventing groundwater infiltration is reinforced, and a constant temperature is kept inside the tomb.

Geotechnical and hydrogeological investigations were conducted as a basis for methods to conserve the Muryong Royal Tomb, one of the most significant Korean cultural properties. First, long-term monitoring of wall-structure movement using the tilt-meter system examined the structural stability of the tomb. Second, an artificial recharge test was performed to analyze the major seepage pathway observed inside the tomb during the rainy season. Measured movements of the wall structure indicate that the tomb has a structural safety problem, caused by a front chamber constructed following excavation. The recharge test and its numerical simulations showed that the major seepage source is the downward flow of water in the unsaturated zone through cracks in the protective layer above the tomb. A plan conservation suggests refilling the front chamber of the tomb to reestablish the original state prior to excavation and to reinforce the protective layer by an effective waterproof material.

This paper presents a methodology and solution procedure of the time-dependent body-fitted coordinate (BFC) method for the analysis of transient, three-dimensional groundwater flow problems characterized by free and moving boundaries. The technique consists of numerical grid generation, time-dependent body-fitted coordinate transformation, and application of the finite difference method (FDM) to the transformed partial differential equations. Based on the time-dependent BFC method, a three-dimensional finite-difference computer code, BFC3DGW, was developed and used to solve two unconfined flow problems. The code was verified by comparing numerical results with analytical solutions for a steady-state seepage problem. In order to demonstrate capability of the method in dealing with flow problems with irregular and moving boundary surfaces, an unconfined well-flow problem was solved by the developed code. Difficulties associated with the free and moving irregular boundary have been successfully overcome by employing this method.

Based on the body-fitted coordinate (BFC) method, a three-dimensional finite difference computer code, BFC3DGW, was developed to simulate groundwater flow problems. Methodology and solution procedures of the BFC method for simulating groundwater flows, particularly when the flow domain is stationary as in the case of confined aquifers, are described. The code was verified by comparing numerical results with analytical solutions for well-flow problems in an isosceles right-triangular aquifer. An example simulation is made to demonstrate capability of the code for solving flow problems in anisotropic aquifers where directions of anisotropy change continuously. The method differs from the conventional finite difference method (FDM) in the ability to use a flexible, nonorthogonal, and body-fitted grid. The main advantages of the method are the convenience of grid generation, the simplified implementation of boundary conditions, and the capability to construct a generalized computer code which can be consistently applied to problem domains of any shape.

A focused electron (E)-beam with various doses was irradiated on the intended positions of conducting polypyrrole (PPy) single nanowire (NW) to fabricate nanojunctions. The current-voltage characteristics and their temperature dependence of the PPy single NW with nanojunctions were measured and analyzed. By increasing the E-beam dose and the number of nanojunctions, the current level of the single NW was dramatically decreased, and the conductance gap became more severe as the temperature decreased. The charge transport behavior varied from three-dimensional variable range hopping to fluctuation induced tunneling models, depending on the dose of focused E-beam. From micro-Raman spectra, the focused E-beam irradiation induced the de-doped states and conformational modification of polymer chains in the nanojunctions. The results suggest that the nanojunctions made by focused E-beam acted as a quasi-potential barrier for charge conduction in the conducting PPy single NW.