No abstract

Numerous studies in biological and chemical processes have been conducted in Lake Suwa, only a few of which were concerned with physical processes that strongly affect a lake' s biochemical dynamics. To gain a better understanding of the corresponding physical dynamics (e.g., current pattern and discharge), we deployed an updated current instrument (i.e., an Acoustic Doppler Current Profiler, ADCP), which is accepted world ･ wide for its accuracy and high resolution as well as for its ability to resolve the spatial and temporal variations of currents. Using the ADCP, we measured discharges of the dominant inflows and current patterns of a submerged macrophytic area near the shore together with an outflowing area (nearby Kamaguchi floodgate). Our results show that (1) the discharges observed in the dominant inflows (the Kami, Miya and To rivers) are different from those reported by Nagano Prefecture, whereas the outflowing discharge at Kamaguchi Floodgate is similar to that in the Nagano Prefecture report, and (2) the vertical distributions of velocity outside the submerged macrophytic area differ from those inside the area, whose horizontal velocities were reduced by macrophyte-induced turbulence, and (3) the current patterns near the outflow showed a strong velocity in the northeast, rather than in the southwest region.

Landslides sometimes occur on mountain slopes by heavy rains. Some of them change into debris flows and then move into mountain rivers. The debris flows erode the river bed and increase their discharge. Prediction of debris flow discharge becomes important for the simulation of flooding debris flows along the river. The purpose of the present study is to develop a prediction model of the landslide-induced debris flow hydrograph. This study is composed of three steps. First, we assume a transformation model of landslide into debris flow. Second, we calculate the development process of debris flow in the middle reach and determine the debris flow discharge. Finally, we simulate the flooding process of debris flow in the downstream reach.

Disaster prevention information systems should maintain high levels of reliability for information. Internet Bulletin Board Systems (BBS) occasionally include inaccurate, malicious or incorrect information. Anonymous posts to bulletin boards are particularly unreliable. BBS should not serve as primary means for official communication. Moreover, most local governments are hesitant to issue evacuation orders despite the urgency of timely announcements because of the suddenness of debris flows. In the current study, we developed a disaster prevention information system using a combined Geographic Information System (GIS) and Social Network Service (SNS) called giSight. The function of SNS is to keep the reliability of information at a high level by registering users. A hazard map of landslide and debris flow is indicated on the GIS with high-resolution aerial photograph tile maps. This hazard map identifies the mesh polygon with dangerous conditions in real-time, i.e. dynamically. This system is not only useful for disaster prevention, but is also expected to facilitate the exchange of information by residents in normal circumstances.

Wind has an important role in the behavior of lake current. In this study, the field measurement of wind and current distribution was performed simultaneously in Lake Suwa. The results proved the spatially nonuniformity of wind distribution over the lake and counterclockwise horizontal water circulation in the lake when the strong north-west wind was observed. It was examined the effect of spatially non-uniform wind on the lake current using a quasi 3-D numerical model by comparing with the calculation result when the spatially uniform wind all over the lake was assumed. In result, the horizontal water circulation obtained by the field measurement was recognized by considering the measured wind distribution. This showed that spatially nonuniformity of wind distribution had a great influence on the movement of lake current.