Water retention curve is one of the most important properties of soil. In previous works, its range less than or equal to pF3 has been mainly focused due to significance of phenomena in wet condition and short of experiment data at high suction. In this research, extrapolation of water retention curve in high suction range is examined using particle size distribution of a soil. Soil moisture covered with mono molecular film of H2O is estimated accurately from specific surface of a soil which is obtained from the particle size distribution, and coincides with experiment data. van Genuchten's formula in wet condition and Brooks and Corey's one in dry condition are applied in order to extrapolate water retention curve. Five types of soil are employed to validate the proposed method and it shows that extrapolated curves have good agreement with the experiment data. It is possible physically to extrapolate the curve in high suction range without experiment data by means of the proposed method.

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The technique of using microwave radar to remotely observe surface soil moisture is based on the principle that the backscattering coefficient θ0 depends on the dielectric constant ε which is strongly related to the volumetric soil moisture content θ. In this study, both the ε vs. θ relationships and the σ0vs. θ relationships in three types of soil (alluvial soil, diluvial soil and volcanic ash soil) which are found in agricultural land were investigated experimentally. The results obtained were as follows:1) The ε (measured with the TDR system) vs. θ relationships in the three tested soils were significantly different from the common relationships derived by Topp et al. (1980). The peculiar dielectric properties in the three tested soils resulted from the well-developed aggregate structures and low dry bulk densities.2) There were large differences found in dry soil conditions between the σ0 vs. θ (within the top 2cm layer) relationships in the three tested soils and the soil examined by Bruckler and Witono (1989). These differences were considered to result mainly from the differences of the dielectric properties in these soils.

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Relation between discharge and temperature is studied in the Qira River in the Tarim Basin, China. Analysis of discharges obsereved at every 30 minutes and hourly temperatures shows that runoff is subject to diurnal variation, daily peak of discharge increases as daily maximum temperature becomes higher and daily discharges are well estimated by accumulated temperature excess over 14°C in a day on cases when the daily maximum temperature exceeds 14°C without rain. It is also shown that peak discharges caused by rain are not larger than daily maximum discharges obsereved on non-rainy days. These suggest that the major source of the river water is melting of glacier on the mountain area in the warm season. The relation between daily total discharge and the accumulated temperature indicates that hypothetical temperature rise in summer by 3°C would cause the runoff 1.3 times as much as toal discharge observed in July and August in 1994.

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The information on the distribution of snow depth in wide area has been requested for long time. In this study, a method is tried for its estimation by using satellite data, TIDAS and N-LAND database compiled from NOAA/AVHRR. Firstly, snow area on a satellite image is detected by using multi-spectral channel. Secondly, in order to make a cloud free image, cloud covered area is replaced by data from adjacent days images. Thirdly, the distribution of snow depth is estimated from the relationship between elevations and snow depths. This relationship equation is obtained from AMeDAS data and GIS data and applied on snow area. Snow depth distribution maps are obtained in Tohoku district from 1989 to 1991. From those maps, the water resources volume of snow is evaluated.

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After volcanic eruptions, debris flow can be triggered by minimal rainfall, which would other wise never cause a debris flow. This suggests that the infiltration rate of the volcanic ash covering the original soil surface is very low. Low infiltration rates of volcanic ash are anticipated due to the presence of clay. This research investigated the hydrological characteristics of volcanic ash deposits to observe the changes in the saturated hydraulic conductivity and infiltration rate under the influence of the presence of clay. Laboratory experiments were carried out on the three kinds of material: (1) volcanic ash from Mount Unzen, (2) volcanic ash from Mount Sakurajima collected at a nearby riverbed, and (3) a mixture of volcanic ashes from Mt. Sakurajima and Mt. Unzen. The results showed that the infiltration rate of the volcanic ash from Mt Unzen was low; approximately 14 mm/hr. It was approximately one third smaller than the infiltration rate of the volcanic ash from Mt. Sakurajima. Also as the clay content increased, the saturated hydraulic conductivity and constant final infiltration rate decreased. The clay content change of low-clay-content ash had a greater influence on changes in the saturated hydraulic conductivity and constant final infiltration rate than the clay content change of high-clay-content ash.

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We made the raingage of light-weight and low-cost (Simple raingauge), which is composed of a pet bottle of soft drinks and a funnel. We compared the observation between this raingauge and tipping-bucket raingauge. The accuracy of observation was within +10% in case rainfall was over 10mm. The raingauge with a fence, preventing rainfall from dropping in and out, showed lower accuracy. We can conclude that this simple raingauge is practical enough in case rainfall is over 10mm.

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