Base flow from 66 tributaries in watersheds underlain by serpentinite, granite, and Paleozoic shale were measured in Oe-yama region, Kyoto Prefecture, Western Japan. The base flow measurements sufficiently after rainfall were conducted during the snowmelt season (April) and summer dry season (August). Spatial variation of specific discharge was greater in the serpentinite basins than those in the granite and the Paleozoic shale basins. In addition, there are many tributaries without discharge in serpentinite basins, even though they have large drainage areas and well-defined valleys. On the contrary, the specific discharges in the granite and the Paleozoic shale basins are relatively constant among tributaries. The average specific discharges in the serpentinite basin are smaller in August than that in April, whereas little difference between base flow discharges of April and August were observed in both the granite and the Paleozoic shale basins. These findings suggest that the seasonal variation of groundwater table level in bedrock is larger in serpentinite mountainous region than that of the granite and Paleozoic shale areas. Hence, we expect that lithology has a crucial effect on spatial variation, quantity and seasonal change of base flow.

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Modified Tank Model which explicitly simulates surface runoff is proposed in this paper. The surface flow as applied here refers to the flow which travels through surface layer. The surface layer is considered as very porous compared to the lower soil layer which is occurrence domain of delayed components. Delayed components of total hydrograph are simulated by conventional tanks. The model is verified in a number of tropical basins located in Kenya and the results compared with previous studies based on Tank Model. The comparison revealed that new tank structure having a provision for surface runoff simulation is effective in improving results.

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A set of DDC Rule Curves which indicate water supply cut ratio given current time and reservoir storage volume was developed. DDC Rule Curves are named so since they use seasonal drought duration curve (Seasonal DDC) as deterministic sum of the future stremflows. The developed is the modified DDC Rule Curve that is designed to utilize the sideflows between upstream reservoirs and the water intake. It was shown that the modified DDC Rule Curve can utilize the sideflow more effectively than the original DDC Rule Curve.

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A field observation was conducted at a reed field which locates near the mouse of Tama river in Tokyo, in which turbulence in and above reed canopy, deflection of reed and transport of sensible heat were observed. The turbulence was found to have a structure of 3D organized vortices which are induced by a shear instability near the top of the plant canopy. The vortices were observed to be composed of strong sweep and weak ejection. The waving of reed termed honami was induced by the organized vortices. The temporal fluctuation of temperature shows ramp pattern, for which the correlation between the velocity and the temperature fluctuation is not linear. The present observation suggests that the organized vortices are the major agency for exchange of fluid momentum, heat and other substances between in and above plant canopy.

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Using a potted tree of Biota orientalis Endl. in a glasshouse, relationships between acoustic emission (AE) rates and transpiration rates were investigated experimentally. We hypothesized that sap flow caused by transpiration resulted in production of AE. Using AE measurements, the main objective of this study is to examine the possibility of estimating transpiration rates directly under drying process of a soil. From preliminary experiments, it was found that AE rates were strongly related to transpiration rates in the plant used in the frequency range of 500-1000kHz. Therefore, AE rates at this frequency range and transpiration rates were measured at decreasing soil water contents. As a result. AE measurements on both a branch and a trunk showed linear relations between AE rates and transpiration rates in the above frequency range. It was also found that these relations were established within a range up to a soil suction of pF 2.6 and abruptly collapsed thereafter.

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Observing the gross rainfall, throwfall, stemflow and soil moisture, we found out the existence of fog drip and estimated its amount. At the same time we explained the meteorological conditions for occurrence of fog drip. As a result, the amount of fog drip during the observational period was 94mm and 90mm in broad leaved and coniferous trees, respectively. Those are correspondent to about thirty percent of gross rainfall and are not ignorable value for water management.

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The comparison of short term runoff characteristics of four catchments have been carried out. Rainfall and outflow records have been investigated for two adjacent catchments (a reclaimed farmland and a natural forest) at Gojo Yoshino area of the Nara Prefecture and two reclaimed farmland catchments at Tango area of the Kyoto Prefecture. The results obtained showed that flood concentration time shortens remarkably by farmland reclamation. The resistant law of the overland flow takes Manning law for reclaimed farmlands. On the other hand, it takes between Darcy law and Chezy law for a natural forest. Equivalent coefficients of roughness decrease obviously due to land reclamation. Limited retention of a natural forest is from 1.4 to 1.9 times as large as that of reclaimed farmlands. Peak runoff coefficients varies in compliance with rainfall pattern and effect of antecedent precipitation. Peak specific discharges of reclaimed farmlands calculated by rational formula are from 2.0 to 2.6 times as large as that of a natural forest.

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In this study, dispersion phenomenon inside the saturated porous medium have been discussed applying mixing length theory concept, which is usually used for the turbulent mixing of the particles in surface water regimes. According to this theory, dispersion coefficient can be expressed as a product of the mixing length and the standard deviation of the pore water velocities. It is shown that the dispersion mechanism is different in saturated and unsaturated flow because the change in saturated flow velocity is attributed to the change in hydraulic gradient while the unsaturated flow velocity changes due to the different degrees of saturation of the porous medium. To check the model for dispersion coefficient and see the characteristics of mixing lengths with respect to grain sizes of the medium, miscible displacement experiments under saturated conditions were carried out using three different sizes uniform glass beads as porous media. Coefficient of variation at saturation, a parameter in saturated dispersion coefficient model, was determined from soil characteristics curves, i.e., suction-moisture content and hydraulic conductivity-moisture content relationships. Mixing lengths for a particular medium were found almost constant which assumed a value of 1.8 times the grain diameter of the medium. The applicability of the model for the dispersion coefficient, for saturated condition, based on mixing length theory concept was checked by experimental data.

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In spite of a great deal of study executed in the past, the optimum dam control for water supply has not been realized in dam operation offices actually. The reason of this difficult condition seems not only because there is no practical and easy mathematical model but also because technologies of long term inflow forecasting and drought damage evaluation are undeveloped. However, practical and easy system model can be formulated by the introduction of statistical factors into classical theory of mass-curve or reverse residual mass-curve. According to the dam control simulation supposing normal range of evaluation functions to the model, the difference of drought damage is unexpectedly small. Therefore, high level dam water supply control is achievable even if future inflow and evaluation function are unknown. As this fact has not been informed precisely to the engineers in the world, this paper explains the theory of the method. In this paper water supply dam control theory is only applied for city water and agricultural water, and power generation control depends on another theory.

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