Yutaka Takahasi

Modelling of hydrologic processes in a small natural hillslope basin, based on the synthesis of partial hydrological relationships

Abstract The authors have equipped a natural small experimental basin, with a catchment area of 4.4 ha, in the Tama Hills in the western suburbs of Tokyo, Japan. It has not only precipitation and streamflow gauging but also soil moisture measuring instruments and groundwater observation wells. At first, based upon the observed data, the partial hydrologic processes such as direct runoff, rainfall-loss, groundwater runoff, groundwater recharge, and evapotranspiration are analyzed. Then a daily hydrological model and an hourly hydrological model are constructed by synthesizing the results of the above analysis, and their applicability is examined.

Modelling of hydrologic processes in a small urbanized hillslope basin with comments on the effects of urbanization

Abstract A small urbanized experimental basin with a catchment area of 2.8 ha, in the Tama hills in the western suburbs of Tokyo, Japan, called the Nagayama Basin, has been studied. The site has rain-recording and streamflow gaugings as well as soil-moisture measuring instruments and groundwater observation wells. Initially, based upon the observed data, the partial hydrologic processes, such as direct runoff, rainfall-loss, groundwater runoff, groundwater recharge, and evapotranspiration, are respectively analyzed. Subsequently, daily and hourly hydrological watershed models are constructed by synthesizing the results, and their applicability is examined. Finally, these models are compared with the models obtained for a natural experimental basin with a catchment area of 4.4 ha, located on the same Tama hills, and the effects of urbanization on hydrologic processes are commented on.

History of Water Management in Japan from the End of World War II

The history of Japan after the Second World War is a dramatic story, which ranges from miserable poverty to an economic prosperity that reached a surprisingly high economic level, but is now suffering from a difficult downturn. To cope with the changing socio-economic transformation over 60 years, water management has also undergone a radical development, with large-scale river projects for flood control, water resources development and environmental measures. The Japanese experience would benefit current developing countries, especially Asian monsoon countries, because they are now actively developing flood control measures, water resources development projects and also conservation work.

Towards a Solution to the North‐South Problem

One of the most important issues in avoiding a global water crisis is to solve the confrontation between developed and developing countries. As Japan in the 20th century has experienced the shift from a developing country to a developed country, it should candidly share its precious historical experience, both its merits and demerits, with people throughout Monsoon Asia. Two practical proposals to economize water demand are as follows: to economize toilet water in a way that meets the conditions of each region; and to develop the effective utilization of water for irrigated rice paddies, not only in the Monsoon Asia but throughout the world. In short, new life-styles are necessary if the global water crisis is to be averted.

Towards a New Philosophy of River Engineering in Japan

Rivers are an important part of nature. River regime always changes in accordance with natural law. Rivers react to human activity including river works, often with an undesirable effect. River management must be planned sensitively from upstream to the sea. River basin management is necessary for flood control, water resources development and conservation.

Water Resource Development and the Environment in Japan

Abstract Large dams contribute to a more reliable supply of water for various uses, flood control and hydroelectricpower generation.They also have social and environmental impacts. This paper reviews the history of the impacts of dam developments on the natural and social environment in Japan, and the countermeasures taken to reduce the adverse impacts. Finally, the implications of the Nagara River Estuary barrage are analysed.

Overview of rivers and water resources in Japan

This paper describes the climatic and topographical characteristics of Japan. Derived from these conditions, Japans rivers tend to be short and precipitate, and severe flooding has been common since early times. Since the end of the last century widescale river improvement works have been undertaken for various reasons. There has been a rapid increase in the productivity of farm land as a result of improved irrigation, and the industrialization and urbanization of Japan have been facilitated. Problems have arisen, however, particularly in regard to pollution and landscape degradation.