The outlines of the main research on runoff analysis for flat low-lying areas in Japan are described. The reproducibility of water level in a drainage canal was investigated under some boundary conditions (the water levels of the two ends), and the degree of difference between the usual analytical method, i. e., the flat low-lying area tank model, and the unsteady analysis was tested. The results showed that when water depth is small, calculation error is large and the calculated values for a flat low-lying area tank model, on the whole, are smaller. On the basis of these results, an improved flat low-lying area tank model (in which unsteady flow is applied only to the main canal) is proposed. A comparison of the difference in the water level reproducibility between the usual and the improved model was performed using a numerical, experiment. From the results, it is anticipated that the improved model can improve the accuracy.

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Heavy demand for water arises in summer, from June to September, because of paddy field irrigation and the increase of domestic water use. A water supply project in Japan usually takes a drought year, which has a return period of 10 years, as the design year, taking account of the present technical level and socio-economic situation.
The development of water resources in Japan is usually designed to serve multiple purposes, i. e., agricultural, domestic, industrial, etc., rather than designed to meet each of those purposes separately. Some facts about water resource usage, drought discharge of river flow, the design drought year concept, low flow analysis and the water require ments employed in designing integrated water supply projects in Japan are explained in this paper. The Ryochiku Water Supply Project in the Chikugo River basin in Northern Kyushu is taken up as a case for study. Also explained in this paper is a way to regulate the discharge with a canal linking two rivers and a way to determine the optimum discharge of a pumping facility, which is necessary to determine the reservoir conserva tion storage. The method of calculating the trade-off relationship between the conserva tion storage of the reservoir water and the maximum discharge of pumping facility is shown in Figure 5.
It is estimated in Japan that the total demand for water will increase. If a severe drought longer than that of the design year occurs the reservoir will come close to depletion, and the basic project plan will not be useful for supplying water. Therefore, it has become more important to set up a higher-level water management system for minimizing drought damages.

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Intensification of water management has been closely watched by developing countries, because it may bring them a higher productivity in agriculture at low cost and in short term. This expectation may be reasonable, but it is not so easy to attain the aims.
In Japan, water management was continuously intensified because of tight water balance before the period of high economic growth. Then, it changed direction and has been taking the way of extensification due to the shortage of labor. This experience in Japan shows that there is an optimum intensity in water management under certain circumstances.
Referring to this experience, some suggestions for the improvement of water manage ment in developing countries are given in this paper.

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The modelling of river basins is an efficient tool for the better management of water resocurces. A reliable model for the practical use will be obtained from detailed basin studies. The capability of a distributed storage model which is derived from the histori cal view of model building is described here, and its application to the practical problems in water management is discussed. It is shown that the simultaneous computation of long-term and short-term runoff is useful for the estimation of a design flood and for flood forecasting. The runoff processes which must be clarified in basin studies are described according to such model applications. The need for of research basins in developing useful models and realizing the rational water management is stressed through a brief sketch of recent basin studies in Europe, where there is a long history of hydrological studies.

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Water is essential not only for human living, but also for agricultural productivity in semi-arid areas. Construction of a large dam for water resources development is surely the most efficient and reliable way to increase and guarantee a water supply. However, in Thailand, a considerable portion of arable land will not be able to benefit from water resources development.
In Thailand, more than 85 percent of the 18 million hectares of the arable land is cultivated under rainfed conditions. Even after the full development of probable water resources projects, about 80 percent of the arable land will remain without reliable water.
In Northeast Thailand, with 40 percent of the nation's total available land, only 10 percent is irrigable from reservoirs, small tanks and pumps. No remarkable development can be expected, since this area is blessed with only the Mun, the Chi and a few other reliable streams other than the Mekong River. No substantial crop production takes place in the dry season due to lack of water.
Therefore, water conservation in the rainfed area is a significant means to obtain stabilized crop production.
Our study team, representing Kyoto University, Chulalongkorn University, and the Royal Irrigation Department of Thai Government, has taken notice of the similarity in natural conditions between Northeast Thailand and the Toban area, Hyogo Prefecture, Japan, where a small dam system has been developed since ancient times through farmers' group activities. Comparative studies* on the rural development in the Toban district in Japan and Northeast Thailand made it possible to introduce a rural development model, which is based on the historical development process of water management technology in the Toban district.
This model, named the Toban model, has been discussed by the research team, refined and improved repeatedly, and applied to an experimental village, Non Khwao, in Khon Kaen.
With reference to the historical process of development in the Toban district, the authors will discuss the applicability of the water management technology in the Toban area to Northeast Thailand from the viewpoint of water harvesting, water distribution, and water control in the village-level irrigation system.

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