Long-term trends of basinwide water balance from 1950 to 1990 in 33 major rivers in the world were examined by using annual precipitation and runoff records, as well as the correlation with El Niño/Southern Oscillation (ENSO). The time series of the annual precipitation and the runoff anomalies show the decreasing tendency of precipitation and runoff in Africa, Asia and Eastern part of Russia, and the increasing tendency in North America. The lag-correlation between the precipitation and the Southern Oscillation Index (SOI) showed the annual precipitation in North America and that in Europe had negative correlation with the SOI at the same year and that of one year before, respectively. The time series of annual precipitation and runoff in North America had a negative correlation with those in Europe. In addition, the time series of annual runoff in Africa had a negative correlation with that in North America and Europe. The analyses in this study were based on annual basis. Further analysis based on seasonal or monthly basis may leads to the clearer results.
The relations between apparent dielectric constant and volumetric water content of Akeyo sandstone, Kimachl sandstone and Shirakawa tuff were tested to measure the water content of rock by the time domain reflectometry (TDR) method. In addition, the values of apparent dielectric constant under three different conditions of the TDR probe installation were compared, as well as the effect on the existence of crack in a rock specimen. Moreover, to understand the effect of high temperature, the apparent dielectric constants of dry rock specimens were examined by changing the temperature from normal one to 80℃.
The apparent dielectric constant measured by the TDR method sensitively increased with the increase of the volumetric water content of rock specimen, showing that the TDR method is applicable to measure the water content of rock. However, under the same water-content condition, the apparent dielectric constant significantly changed when the probe installation method was different. In particular, the apparent dielectric constant was underestimated when air had remained in gaps between the probe rod and the guide hole in the rock specimen. The improved piston-type probe, which was developed in this study, could minimize the effect of the gaps. Comparison between the apparent dielectric constant of rock specimen with single crack and that of intact rock specimen showed that the apparent dielectric constant obtained by the TDR method was influenced by the existence of crack in the specimen. In particular, when air remained in the crack, the apparent dielectric constant was notably underestimated. The apparent dielectric constant of dry rock specimen slightly increased with the increase of temperature. This result suggests that the apparent dielectric constant of wet rock likely to change significantly with the increase of temperature, because the dielectric constant of water is sensitive to the change of temperature. Further investigation is necessary to reveal the effect of high temperature on the apparent dielectric constant of wet rock.
Laboratory measurement of the hydraulic conductivity of various rock types revealed that the hydraulic conductivity sensitively changes as the porosity and the stress state in the rock change. This effect becomes clear when the porosity and various principal stresses are increased. Review of the previous laboratory experiments indicate that the hydraulic conductivity of various rock types ranged between the order of 1O-11cm/sec and 100cm/sec, and it decreases as pore pressure decreases, confining pressure increases and intermediate principal stress increases.
The variation and distribution of hydraulic head and hydraulic gradient within a specimen were evaluated by a general equation which describes the transient pulse test. The hydraulic gradient during the early stage of the transient pulse test remarkably increased at around the upstream end of the specimen. As the time elapsed, the hydraulic head at the upstream side gradually decreased, whereas that at the downstream side monotonously and gradually increased.