For reservoir operation, stochastic approaches to the storage variation are integral because temporal variation of volume of inflow and intake in a reservoir is uncertain. It is needed to define reservoir reliability appropriately, for each reservoir has a characteristic operation rule. In this paper, reservoir reliability is defined as the probability such that the storage remains in a prescribed admissible storage domain until a prescribed final time provided that the current storage is observed in the admissible storage domain. Since the storage equation proves that the storage is a continuous Markov process, it is deduced that the reservoir reliability is governed by the Fokker-Plank partial differential equation. Furthermore, a numerical method is developed to solve the governing equation using the finite element method. A sample analysis is made for the Yasugawa dam which located in Shiga prefecture to represent practical application of the methodology developed.

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A numerical hydrological model that is universally applicable in large low plain area is developed. In this paper, common characteristics of large basin area such as channel network connecting with lakes and ponds are described in detail and the hydrological processes can be simulated by the numerically combined method between two-dimensional model for large lake and one-dimensional model for channel network. This model has been calibrated against the observed data in 1984 and 1985 from May to September in Taihu Lake Basin, China. From the result, good agreement between simulated water level and discharge to those from the observation data was indicated and therefore, this model satisfies the hydrological processes for practical use.

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Well connected macropores running almost parallel to surface, are commonly found in forest soil. It is called “soil pipe” and water flow which go through them are called “pipe flow”. This paper reviews the studies on the influence of water flow in soil pipe on slope stability with regard to rainfall intensity, and present a guideline for more practical discussion. In the case of normal rainfall event, soil pipes contribute to quick discharge of rain water which result in slope stability. Soil pipes, however, are a dead-ended pathway, which do not always work for rapid runoff system and induce slope failure. On the other hand, in the case of large rainfall event, soil pipes may not contribute to slope stability through excess infiltration beyond the drainage ability of lateral pipes and they are collapsed by underground erosion. These phenomena bring about high pore water pressure and slope failure. In order to understand and evaluate the influence of pipe flow on slope stability, three aspects should be studied: 1) are these phenomena universal? 2) quantative evaluation of influence on rain-runoff process, 3) how do they change their structure?

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The World Bank, U.S.A. and U.K. decided, in December 1955, to provide Egypt with funds for then planned High Aswan Dam by loan and grant. The U.S.A. however cancelled the once pledged aid in July 1956. The U.K. and the World Bank also cancelled their financial assistance. In the same month, as a revenge, the Govermment of Egypt nationalized the Suez Company which was then owned by U.K. and France. This induced the Suez Crisis in October 1956. The major reason of U.S.A.'s withdrawal was Egypt's having closer ties with U.S.S.R. and Eastern European countries. Additional reasons are: opposition in the U.S. Congress by those elected in the southern states, Eisenhower administration's willingness to avoid competition with U.S.S.R. in terms and conditions of foreign aid, protests shown by allied developing nations, Egypt's disagreement to the terms and conditions of the proposed aid, and lack of agreement with Sudan . The same incident, an international crisis, is unlikely to be caused in these days, for (i) there now exists various mechanisms to meet requirements of developing nations, and (ii) recipient countries have understandings about conditions attached to financial aid by donor countries and organizations.

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The evapotranspiration rate was calculated by Thornthwaite-Holzman model from the data obtained in a deciduous broad-leaved secondary forest in Yamashiro Town, Sohraku Country, Kyoto Prefecture. The parameters showing the effectiveness of sensible heat exchange in this model were estimated to be 0.12 in a foriaged season and 0.077 in a defoliated season, i.e. the former is 1.5 times as high as the latter. The maximum daily rate of evapotranspiration was stable and estimated to be about 12MJ/(m2·day) in a foliaged season. On the other hand, those calculated in a defoliated season varied widely from about 2MJ/(m2·day) in January to 6-7MJ/ (m2·day) in November and April. In comparison of the result calculated by Thornthwaite-Holzman model with that introduced by Bowen ratio method, it was revealed that Thornthwaite-Holzman model is able to estimate more accurately in a defoliated season, and give no less accurate estimate in a foliaged season than Bowen ratio method does. The ratios of evapotranspiration against effective radiation were estimated to be about 40% from January to April and about 60% from June to November. The increase of this ratio delayed about one month from a leafing time. Moreover, these ratios were almost equal to those in a Japanese Hinoki forest and a Swedish pine forest, although there were differences in a seasonal variations.

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In the transition to a market economy, in the rural Vietnam areas, the right to conduct production subjectively has been returned from cooperatives to the farm households. This individualization motivates the farmers to carry out their farming practices effectively. However, onfarm water management, because of physical interdependency among the farmers, can hardly be effectively carried out without cooperation of all the interdependent farmers. This paper, based on case studies of the main types of onfarm water management prevailing in the Red River Delta, analyses the changes in onfarm water management in the transition. It is found that, while the farmers carry out farming practices individually, the diminishing of the cooperative's role in onfarm water management is the main cause of the onfarm facilities' damages and unreliability of water supply to downstream area. The downstream farmers, depending on the changes in the role of cooperative in water management, take different countermeasures. In the best cases where the cooperatives can mobilize resources for a supplemental water supply, the farmers have to spend much more money and labour than the upstream farmers. In the other cases, they could not do anything other than to suffer from water shortage and delay water fee payment. The equity policy in water distribution and cost payment would enable the downstream farmers to invest in water recycling, thus increasing the system's efficiency. The integration at the village level of hamlet traditional organizations would be an effective body for onfarm water management.

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