To investigate the characteristics of direct runoff in a forested mountaious watershed, this study analyzed the relationship among precipitation, initial runoff, and direct runoff in the Fukuroyamasawa Experimental Watershed (35°12' N, 140°06' E, 2 ha) in University Forest in Chiba, The University of Tokyo, Japan. The watershed is located in a Tertiary formation and is covered by a mature mixed plantation of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) trees. Annual precipitation is 2170 mm, and annual mean temperature is 14.2 °C . In 1999, part of the watershed (1.1 ha) was clear-cut. Direct runoff increased as precipitation or initial runoff increased. Equations with three parameters were formulated to express the relationship among precipitation, initial runoff, and direct runoff. Direct runoff was accurately estimated by the equations(R² > 0.94). The effects of precipitation and initial runoff on direct runoff were synergistic. The parameters of the equations changed after forest cutting. The effect of vegetation on direct runoff was found to depend on the size of the storm and was relatively high after medium-sized storms(about 100 mm). The relationship between initial runoff and direct runoff appeared to change in response to changes in the characteristics of moisture distribution in the watershed after clear-cutting.

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The increases in water demand associated with rapid socio-economic development led to water shortage in the northern part of China, such as in the Yellow River basin. Nowadays, the use of agriculture water is beginning to be restrained by the increase in new water uses, such as industrial water and domestic water; and by rapid pace of industrialization and urbanization. However, it is significant to secure agriculture water to meet the increasing and diverse food demand of its growing population. Subsequently, the Chinese government plays a central role in the efforts to overcome the water shortage, such as in the ‘South to North Water Transfer Projects. In order to resolve the issue of such water shortage, it is important to understand how water can be used in the most physically and economically efficient way, and the extent on how much water use can be reduced in what regions. The effective and rational use of agriculture water is necessary if the country is to achieve a sustainable agricultural production. From this viewpoint, we applied DEA (Data Envelopment Analysis) techniques to a provincial level dataset to estimate the efficiency of agricultural water use in China. In addition, we compared and examined the differences of efficiencies among the main river basins which are created by the administrative unit on a province level. We also identified determinant factors affecting the efficiencies using the Tobit model.

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Very short-time quantitative precipitation forecasting (nowcasting) using X-band polarimetric radar is proposed as a means of quantitative rainfall estimation to support flood prediction in urban areas. The method includes C-band conventional radar as complementary data. Inland flooding tends to occur more frequently in urban areas due to the large proportion of impervious surfaces, and flooding in such areas is of considerable public concern. Due to the rapid response of rivers and drainage infrastructure in urban areas, nowcasting is required in order to realize timely flood prediction. However, as the X-band has a relatively short observation range and is affected by strong signal attenuation under heavy rainfall, X-band alone are insufficient for nowcasting. In the proposed method, X-band polarimetric radar provides highly accurate rainfall data, and real-time corrected C-band conventional radar provides the gap filling data. The results of the method are demonstrated to accord well with rain-gauge data and superior to a conventional radar rainfall. The accuracy of the proposed method is also comparable to that of Radar-AMeDAS, a radar rainfall method corrected using a high-density rain-gauge network in near real-time. The nowcasting experiments were conducted using the conventional radar rainfall and the radar rainfall based on the proposed method. The results from the three cases showed that the method can improved rainfall nowcasting.

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In order to clarify physical meanings of conceptual runoff models and runoff parameters, models such as the rational method, tank model and storage function model were theoretically derived in this paper. The conceptual rainfall-runoff models are derived by the kinematic wave theory for the subsurface or surface flow with three types of the flow resistance law (Darcy's law, Manning's law and saturated-unsaturaged flow) in a hill slope. From this analysis, it was found that the storage function model was derived by assuming a steady state solution for direct runoff every moment and the tank model was derived if mean surface flow velocity in a hill slope was proportional to the slope length. Furthermore, on the assumption that the flow resistance law took the saturated Darcy's law or under steady state condition, the rational method was derived. Runoff parameters of the tank model and storage function model that have been calibrated using historical rainfall and discharge records can be uniquely determined by the quantities of a surface soil layer such as a saturated hydraulic conductivity, an exponent in hydraulic conductivity function, surface soil layer thickness and an effective porosity from theoretical derivation of the models in this paper.

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In this research, an unmanned helicopter based system has been developed for monitoring river environment. Two digital cameras, two IR cameras, and GPS are mounted on an unmanned helicopter to acquire detailed information from low altitude which is different from a satellite or a plane. The monitoring is carried from the sky, but the resolution and accuracy are very high. The data can be easily acquired collectively with safety and mobility, because of the utilization of an unmanned helicopter. Moreover, unmanned helicopter monitoring has been conducted several years to evaluate usability of the system for river environment changes, such as distribution of plants, geographical features of river, and so on. Also, effectiveness of unmanned helicopter based data has been proven by comparing with existing data such as satellite image.

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SRM (Snowmelt Runoff Model) is a lumped model to calculate daily mean discharge in a mountainous snowy watershed without determining parameters by iteration nor mathematical optimization by using observed discharge data. It was applied to the upper reach of the Uono river basin, Niigata prefecture, one of the snowiest region in Japan. As an input data of SRM, snow-covered ratio in the basin was estimated by Landsat/TM on 26th April, 12th May, and 26th May in 1993. Also, daily mean temperature and daily precipitation at AMeDAS Yuzawa station were used as the input. For validation, daily mean discharge at Muikamachi station of Ministry of Land, Infrastructure, Transport and Tourism was used. Inevitable parameters to drive SRM was partly derived from daily mean discharge at Muikamachi in spring 1992, while other parameters difficult to determine objectively were determined considering the case study of the Okutadami basin using SRM, which is located in ca. 40 km northeastern part of the Uono river basin.
For comparing with previous studies which estimated snowmelt-runoff of the upper reach of the Uono river basin using distributed hydrological model, Nash-Sutcliffe efficiency was calculated from 23rd April to 30th May, 1993. The calculated efficiency between the observation at Muikamachi and the estimation by SRM was 0.82, which is sufficiently accurate to estimate daily mean discharge in the snowmelt season although SRM is a lumped model which has a characteristic mentioned above. Even if snow-covered ratio after 13th May was extrapolated using those of 26th April and 12th May, the calculated Nash-Sutcliffe efficiency during the study period was 0.83. This result implies the possibility of using SRM to calculate the short-to-medium range snowmelt-runoff.

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