In order to clarify the effect of fine pores on the water retentivity of the decomposed granite soil “Masa, ” the authors have examined the relationship between porosity and water retentivity in terms of specific surface for eight samples, in various stages of weathering, stages taken from two outcrops in Shimane Prefecture.
A fine pore is first formed in specified sizes; with weathering its size becomes more variable in decomposed granite soil. At the high potential value over -1×10⁵ Pa, the fine pore content calculated from the water retentivity curves agrees approximately with that measured by the mercury injection method.

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In order to avoid further detrimental impact on development, and to achieve agricultural sustainability, a method of land use adjustment is introduced. Land use adjustment is defined as an activity to determine, based on certain rules for the priority of land use, whether a parcel of land is suitable for a certain utilization. The objective of this study is limited to the adjustment of land suitable for both paddy and settlement and the determination of which of them in a case study area in Yogyakarta, Indonesia. Artificial ranks for land suitability, which is estimated by quantification-2, are employed for the adjustment. The result of analysis shows that this method contributed to land use planning in the identification of land to be adjusted for: (a) paddy fields (and which has been so cultivated), (b) settlements (and which has been so occupied), (c) paddy fields (but which has not been so cultivated), and (d) settlements (but which has not been so occupied). The areas to be conserved, the settlement areas which had grown in an unexpected place, and the land recommended for settlement growth could also be spatially mapped.

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The Scheme Irrigation Management Information System (SIMIS) developed by FAO is a personal computer software package of integrated databases for efficient operation and management of an irrigation system. The Irrigation Scheduling module of SIMIS, which the authors have been responsible for developing, is designed to improve the efficiency of irrigation system management by providing a practical weekly irrigation schedule. The module was used to simulate water management practices on the tertiary canal unit of an irrigation system in Mendoza, Argentina. A new option of water scheduling based on a supply-oriented approach was added to simulate ongoing management practices. The result showed that current management practice based on a supply-oriented approach resulted in a large volume of water loss.
To alleviate the problems of a supply-oriented approach to water distribution, scheduling methods based on a demand-oriented approach were used to simulate management practices for the same tertiary unit. Scheduling methods based on crop water requirements or soil moisture balance could save as much as fifty percent of the water supply needed for the supply-oriented approach. It was found that the introduction of a supply adjustment factor and a weekly rotational supply improved the performance and adaptability of scheduling methods over the demand-oriented approach.

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In many Asian paddy field areas, continuous irrigation schemes are often changed to rotational ones when water deficits become serious. In rotational irrigation, released water advances on a dry bed channel, because the channel bottom dries up during the waiting period for the next water supply. The hydraulic characteristics of released water flow are similar to those of the irrigation advance problem. Although numerous methods have been proposed to solve the problem, they cannot be applied directly to released water flow. A new calculation method devised in this study has the same structure as that of the two-step Lax-Wendroff scheme, and adjusts the tip's infiltration rate by monitoring the whole mass balance. Using this method, the arrival time and arrival rate of released water are examined numerically. These indexes are dependent on many factors, and several factors closely related to O & M are selected to examine their influence. The selected factors are roughness coefficient, infiltration rate, supply duration, and inflow rate. These results are applied to a model irrigation system to compare the conveyance efficiency of continuous irrigation schemes with that of rotational ones. As a result, the following facts are noted. First, a rotational irrigation scheme is advantageous when water deficit is serious. Second, a regulating reservoir can improve conveyance efficiency considerably.

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The purpose of this study is to establish a method using Landsat-5 TM data for the measurement of the turbidity distribution in the interior part of the Ariake Sea, which has great influences on the environment, ecosystem and marine products. The relationship between the turbidity and spectrum of the sea area, the properties of path radiance in TM data, and the procedures for atmospheric correction and measurement of turbidity distribution were discussed on the basis of turbidity and spectrum which were obtained from in situ measurement, and Landsat-5 TM data.
The results indicated that the spectral radiance just above the seasurface in the wavelength range from 0.4μm to 0.85μm was closely related to the turbidity, but that beyond the wavelength of 0.95μm it was almost zero, and the path radiance, which occupied about 90% to 70% of the radiance of TM Bands 1 to 4, was dependent on the law of about-3th power of wavelength. A reasonable and simple method of atmospheric correction for TM data by using the radiance of TM Band 5 which seemed to be equivalent to the path radiance over the sea area and the dependence of path radiance on the wavelength was also presented. Moreover, the turbidity distributions in the study site were exactly measured by the regression equation between the turbidity and the ratio of radiances of TM Band 3 and Band 2 which were corrected for the atmospheric effects.

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The lowering of groundwater levels in the Takaoka basin poses a significant threat to sustainable utilization of its scarce groundwater resource. A transient, two-dimensional groundwater flow model was developed for a single-layered unconfined aquifer system and was solved by the finite-element method (FEM). Using this numerical model, present and future groundwater scenarios for dry periods are presented by simulating various groundwater management strategies. The response of the Takaoka basin to some artificial recharge techniques was also investigated, and two techniques are proposed for its rehabilitation. The model estimated recharge from the Niyodo River to be about 22.24×10³m³/d in a no-pumping situation. A decline equal to or greater than 0.5m in the Niyodo River water level considerably lowers the basin's groundwater levels. Any increase in pumping from the present rate will aggravate the overdraft problem. Modeling results suggest a cutback of about 30% in pumping as a preliminary measure to mitigate groundwater mining. The worst groundwater scenario during drought years emphasizes the immediate rehabilitation of the basin. Further, simulation results of two artificial recharge techniques viz., groundwater barrier and Niyodo River modification-indicated promising potential for rehabilitating the depleting aquifer. While the influence of the proposed barrier is limited, a weir of height 4.5m from the dry period water level in the Niyodo River is sufficient to meet the present groundwater demand and thereby stabilize the aquifer.

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