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IntroductionIn the 1950s and 1960s, there was significant global concern over the capacity of agricultural production systems to produce enough food for rapidly growing populations, especially in developing countries. Episodes of severe food scarcity were frequent, especially in the populous countries of southern Asia. The world community responded to the perceived threat in various ways. A major strategy was the rapid creation of new irrigation schemes. These efforts reached a peak in the mid-1970s, when the world's stock of irrigated land was increasing by about 2.5 percent per annum 2 . Many irrigation facilities were planned, constructed, and managed by the government. Invariably, farmers were not consulted in the design or the management of the irrigation facilities. There is clear evidence to show that the spread of irrigation has been a major contributor to the success of the green revolution in Asia and the remarkable increases in agricultural output. By the early 1980s, however, there was widespread dissatisfaction with the performance of irrigation projects, particularly in the large government-managed canal systems, casting doubts on the efficacy of bureaucratic management in the irrigation sector. The 1980s saw the beginning of a search for a new type of relationship between the managers of the irrigated agriculture sector and farmers. With regard to irrigation, this trend led to efforts to promote a participa- REVIEW AbstractParticipatory irrigation management (PIM) is an approach in which farmers participate in all stages of irrigation development through to operation and maintenance, and is implemented in many developing countries. Irrigation management transfer (IMT), a program of transferring the management of irrigation system from government to local user groups, has also been promoted. However, in most cases these approaches have not been successful, because, for example, of the unfair cost sharing and financial weakness in farmers' organizations. This paper summarizes the current problems of PIM/IMT, proposes basic principles for sustainable PIM, which can be applied to IMT, through a review of the previous studies, and discusses future areas for the sustainable use and management of irrigation systems. The key issues that have contributed to the failure of PIM/IMT are a lack of awareness among farmers of the role and necessity of water users' associations (WUA) and the inherent weakness of WUA. We propose the following principles for functional sustainable irrigation management: (1) The roles of WUA and governance are clear and adequate; (2) Through participation in WUA, farmers are guaranteed that their demand for water is supplied in a timely manner; (3) Farmers receive financial benefits through the use of water, which then allows them to cover the costs of water and associated services; (4) All members are treated equally with respect to water allocation, cost sharing, and decision-making; and (5) Information on the financial status and transactions are disclosed to members of WUA in a...

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Percolation of water from a pond may cause a landslide in a hilled rural area. Before measures to prevent such landslides can be planned, it is essential to identify reservoir-water influent from the pond. We describe an analytical method that uses 222 Rn-and water-balance equations to quantify groundwater effluent and reservoir-water influent simultaneously, which is impossible using the conventional method that measures only surface-water inflow and outflow. We selected F pond, Nagano Prefecture, as the study site. We estimated the rate of 222 Rn dispersion to the atmosphere by assuming a stagnant film between water and air with thickness inversely proportional to the rate of dispersion. By a laboratory experiment, we estimated the film to be about 830 µm thick and found that the film thickness was not influenced by wind velocities less than 1.5 m s -1 . A preliminary investigation suggested that reservoir-water was mixed very well. The groundwater effluent and the reservoir-water influent during the investigation were calculated to be 0.67 × 10 -3 m 3 s -1 and 0.41 × 10 -3 m 3 s -1 respectively, by making 222 Rn-and water-balance equations and solving them. This analytical method is expected to be useful for not only prevention of a landslide but also for effective use of water and prediction of water quality.

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The authors conducted an investigation on shallow groundwater using natural radioisotopes as indicators in the small basin of the Hinuma River, Kasama City, Ibaraki Prefecture, Japan.3H concentrations in the groundwater showed that it originated from precipitation in the 1960's .Since 222Rn concentrations decreased as groundwater flowed downstream, they were influenced by infiltration of surface water. Especially, during the irrigation period, the decrease of 222Rn concentrations was remarkable in the lowland. From the distribution of 222Rn concentrations in surface water, the sections where groundwater seeped into a river were found, and a quantitative analysis of groundwater seepage in the two sections was conducted on the basis of 222Rn concentrations in groundwater and in surface water. The ratios of groundwater seepage to the flow at the upstream station for the two sections were about 5% and 10%, respectively.The water movement within the basin, i.e., the actual manner in which surface water infiltrated underground and groundwater seeped into a river, was clarified by analyzing the variations of natural radioisotope concentrations in water and the water balance of the basin.