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Song S.-H.,Korea Rural Community Corporation | Zemansky G.,Institute of Geological & Nuclear Sciences
Environmental Earth Sciences

Data for the Waimea Plains, New Zealand indicate that the lower confined groundwater aquifer is hydraulically homogeneous and that shallow groundwater levels inland are affected mostly by anthropogenic processes, while those near the coast are affected more by sea level variation. Analysis of long-term data for New Zealand indicates that sea level has increased continuously, but trends are not spatially uniform. Results from non-parametric trend analysis show that rising trends for groundwater levels are predominant in the shallow aquifer both inland on the Waimea Plains and, for recent years, near the coast, while decreasing trends are evident in the underlying confined aquifer near the coast. Groundwater level change in the shallow aquifer appears to be more affected by climate change than the lower confined aquifer. Correlation analysis indicated that groundwater levels are more affected by rainfall during the rainy season than the dry season and more influenced by rainfall inland than near the coast. Groundwater level declines in the lower confined aquifer near the coast, which has its major recharge area inland in the catchment, may be substantially affected by groundwater abstraction in inland areas as well as sea level variation, but there are little evidences of seawater intrusion. Meanwhile, groundwater recharge over the catchment area has great influence on rising groundwater levels in the shallow aquifer and its recharge is estimated to be 417.8 mm/year using chloride concentrations of precipitation and groundwater. © 2013 Springer-Verlag Berlin Heidelberg. Source

Song S.-H.,Korea Rural Community Corporation | Zemansky G.,Institute of Geological & Nuclear Sciences
Environmental Earth Sciences

Groundwater systems in coastal aquifers may be affected by sea level change as increased seawater intrusion occurs with sea level rise. Artificial pumping taking place at the same time will increase this impact. In order to estimate the vulnerability of groundwater systems with sea level rise within coastal aquifers in South Korea, long-term groundwater data were analyzed using basic statistics, trend analysis, and correlation analysis. Conductivity depth profiling was also periodically conducted. Groundwater levels increased in wells with relatively low groundwater elevations but decreased in wells with higher groundwater elevations. At the same time, conductivity variations were greater in wells located in reclaimed land areas, which vertical conductivity profiles indicated were more affected by sea level variations, but decreased on the mainland. Results of auto-correlation analysis showed a decreasing trend with cyclic variations and significant periodic patterns during dry seasons, indicating that groundwater levels were not affected by artificial factors and that those in reclaimed land areas were less affected by rainfall than on the mainland. These results coincided with those from cross-correlation analysis showing that groundwater level was affected by sea level variation during the dry season. Sea level changes, which may be related to climate change, as well as rainfall in South Korea can influence groundwater levels, and the groundwater system in reclaimed land areas may be more affected than on the mainland, especially under dry conditions. © 2011 Springer-Verlag. Source

Kim K.Y.,Kangwon National University | Park Y.-G.,Korea Rural Community Corporation
Exploration Geophysics

Microtremors were analysed using the reference-dependent horizontal spectral (H/H) method and the horizontal-to-vertical spectral ratio (H/V) method to estimate site effects of the Cheongcheon earthen dam in Korea. Seismic vibrations were recorded on the dam's crest, at the toe of the dam, and in a downstream borehole using three-component accelerometers. The H/H peaks for crest versus toe-of-dam accelerations occurred at 3.1, 6.7 and 13.1Hz with ratios of 6.9, 11.4 and 8.9, respectively. The H/V peaks for the crest of the dam occurred at 3.0, 7.0 and 13.4Hz with ratios of 6.7, 7.8 and 5.6, respectively. The peak near 3Hz may correspond to depth to bedrock, whereas the other peaks at higher frequencies may reflect the geometrical effect of the dam or overtone responses to the thickness of dam fill overlying the clay core. For the toe data, from the H/V spectral ratio method, the basement boundary appeared as double peaks near 8 and 10Hz with corresponding amplification factors of 5.2 and 6.2. These may indicate a gradual change in velocity across the basement boundary at ∼10m depth. The third resonance, which occurred at 15Hz, may correlate with the refraction boundary at 5-6m depth in the overburden layer. Both the frequencies and magnitudes of resonance derived from the H/H and H/V methods are reasonably well matched to the theoretical response curves computed by the reflection and transmission matrix and the two-dimensional finite difference methods. © 2016 ASEG. Source

Lee B.,Korea Rural Community Corporation | Mulheron M.,University of Surrey
Magazine of Concrete Research

Two issues make measuring the local bond stress-slip relationship difficult: first, the bar is embedded within the concrete, making measurement of local strain values complex; second, yielding of the steel bar influences the bond stress-slip behaviour. Global bond stress-slip behaviour is generally obtained by measuring the slip that occurs at the free end of the bar during pull-out testing. Several distinct mounting methods have been used to install electrical resistance strain gauges on embedded bars in concrete to obtain local strain data. These methods are reviewed in relation to their ability to deliver reliable and robust data at both small and large values of slip. The use of such strain gauges is found to provide a viable method for assessing the variation in strain along embedded steel bars during pull-out testing. The use of surface-mounted strain gauges leads to high failure rates due to physical damage to either the gauges or their connections. The use of near-surface- and central-groove-mounted strain gauges enables measurement of local bar strain over large displacements. Using data from near-surface-mounted strain gauges, it is shown that in the post-peak region the bond stress increases linearly from the free end of the bar. Source

Lee Y.,Korea Institute of Geoscience and Mineral Resources | Park S.,Korea Institute of Geoscience and Mineral Resources | Park S.,Kongju National University | Park S.,Korea Rural Community Corporation | And 3 more authors.
Renewable and Sustainable Energy Reviews

To estimate available geothermal energy and to construct temperature at depth maps in Korea, various geothermal data have been used. Those include 1560 thermal property data such as thermal conductivity, specific heat and density, 353 heat flow data, 54 surface temperature data, and 180 heat production data. In Korea, subsurface temperature ranges from 23.9 °C to 47.9 °C at a depth of 1 km, from 34.2 °C to 79.7 °C at 2 km, from 44.2 °C to 110.9 °C at 3 km, from 53.8 °C to 141.5 °C at 4 km, and from 63.1 °C to 171.6 °C at 5 km. The total available subsurface geothermal energy in Korea is 4.25 × 1021 J from surface to a depth of 1 km, 1.67 × 1022 J to 2 km, 3.72 × 1022 J to 3 km, 6.52 × 1022 J to 4 km, and 1.01 × 1023 J to 5 km. In particular, the southeastern part of Korea shows high temperatures at depths and so does high geothermal energy. If only 2% of geothermal resource from surface to a depth of 5 km is developed in Korea, energy from geothermal resources would be equivalent to about 200 times annual consumption of primary energy (∼2.33 × 108 TOE) in Korea in 2006. © 2010 Elsevier Ltd. Source

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