To assess a seasonal variation of sap flow (q)and to evaluate forest transpiration (TR) for over daily scale, sap flux density was observed at a several trees in a natural deciduous oak (Quercus crispula Blume) forest located at a steep slope in a headwater catchment. q indicated its maximum value at about 10-days after from the completion of foliation, and decreased during summer and autumn. This decreasing trend corresponded with the seasonal variation of vapor pressure deficit. To validate TR, evapotranspiration (ET) was evaluated by short-time period water-budget method, and interception loss (I) and forest floor evaporation (E_F) were estimated by the previous studies conducted in the same forest. TR corresponded well to transpiration estimated from ET, I and E_F (TR_SPWB = ET-I-E_F). Therefore, we indicated that the measurement of sap flux density is an effective method to evaluate TR in a forest located at a steep slope as compared with the short-time period water-budget method.

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To investigate the formation process of Horton overland flow in unmanaged Hinoki plantation, hydrometric observation and tracer approach were applied in an unchanneled catchment, Mie prefecture, central Japan. An overland flow with a total runoff rate of 15.7 mm was observed during a rainstorm with a total rainfall of 120.4 mm. The peak discharge of overland flow coincided with the peak rainfall, and major solute ion concentrations decreased obviously with runoff peak. End member mixing analysis was applied to evaluate the overland flow components using electrical conductivity and Cl^- concentration as tracers. The ratio of rainfall component to the overland flow was estimated to be ranging from 24 to 84 %. Especially, the rainfall component was predominant in heavy rainfall intensity more than 2 mm/5min. The overland flow occurring in a rainstorm more than 2 mm/5min should be Horton overland flow considering the end member mixing analysis results and runoff characteristics. This shows an importance of the Horton overland flow in rainfall-runoff processes in the catchments covered by unmanaged Hinoki plantations.

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Recently, various river-related disasters have occurred world widely, such as floods or abnormal droughts. On the other hand, influence of global change on regional water management represented as reservoir management have not been discussed sufficiently, although it has been said that some change of climate system has occurred in the global scale. Under such condition, use of more information that has a relationship to each basin should be taken into consideration for more efficient reservoir management. And also, operation rules of each reservoir should be changed along the current hydrological condition.
Therefore, in this study, a heuristic decision support system for continuous reservoir operation considering global meteorological information is proposed to establish more efficient reservoir management.

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Precise flood mapping is a prerequisite for efficient flood disaster management. Flood induced losses can be minimized by means of acquiring precise flood disaster information through mapping of flood prone areas. In this paper, radar remote sensing (RADARSAT) data is used to accurately delineate the distribution of open water inundation during the biggest flood of 1998 in Greater Dhaka City, Bangladesh. Seven flood time imageries and one dry season image were used to identify the precise and widest flooding area that is expected to be helpful for developing apposite flood countermeasures. The radar images were digitally processed to geometrically rectify the pixel geometry and were filtered to suppress speckle noise. The imageries were classified according to flooded (open water) and non-flooded categories using the Maximum Likelihood Decision Rule. The classification accuracy of the radar data were then evaluated using ground reference data. Spatial-temporal analysis of flooding revealed that flood water started to increase from early July 1998 (inundating 34.65%) and reached its peak on 25 August (inundating 51.29%). This was mainly attributed to heavy monsoonal downpour and early peaking of river water levels. The eastern part of the city suffered severe flood damage. In contrast, most of the western part of Greater Dhaka was not severely flooded due to the existing flood control works and relatively higher elevation. Classification accuracy of imageries show that all image in the dataset produced satisfactory results. The highest overall accuracy attained was 88.57% for 31 July image, followed by 7 July and 10 September images, respectively (82.86% and 81.90%). Kappa statistics for all the images were also in good agreement except the August images. The results showed that SAR data is of value for real-time flood monitoring for a fast growing city like Dhaka and can provide the necessary information for flood disaster information and management.

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The NO_3^-N concentration and load during a stormy flood event were investigated in a forested, mountainous headwater catchment in the Shimanto River basin. The experimental catchment is covered with a natural forest of predominately Abies firma and Tsuga sieboldii. Investigations during flood events were conducted for five events. Two types of NO_3^-N concentration variation were found before and after the rainfall event. The NO_3^-N concentration after the rainfall was almost the same as the concentration before the rainfall in three events, of which total rainfall was less than 100mm. In contrast, the NO_3^-N concentration after the rainfall was much smaller than that before the rainfall in two events, for which the total rainfall exceeded 150mm. The amount of NO_3^-N load during flood events increased with increasing of the total rainfall when the total rainfall was less than 100mm. However, for the rainfall events with a total rainfall exceeding 150mm, the increase rate of NO_3^-N load during flood events to total rainfall tended to reduce.

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