It is important for dam owners to prepare an accurate rainfall prediction model which can deal with local severe rain in mountainous regions in order to operate and maintain dams appropriately. So far, our group have tried to develop rainfall prediction models for the Kurobe Valley not only for properly operating the dams on the Kurobe River but also for well providing for flood damages. In this paper, we introduce a newly developed rainfall prediction model. The rainfall prediction model has higher accuracy than exixting models by the following two reasons. The one is that the mechanism of rainfall generation and development, which is remarkable features in mountainous regions, is formulated in the model. The other is that the extraporation model and the meso-scale atomospheric model are optimally combined, aiming to incorporating advantages of each model. The results by this hybrid model, linked with a distributed runoff model which is made separetaly, have already utilized for acutual dam administration works.

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We analyzed the relationship between abundance of cyanobacteria and stability of density stratification in several eutrophic reservoirs in Japan. Under weak stratification conditions, which corresponded to N ² = O (10^-4) - O (10^-3) (s^-2), cyanobacteria rarely formed water bloom. In reservoirs where artificial destratification equipments were installed, N ² and the abundance of cyanobacteria decreased. The difference of the minimum N ² in which cyanobacteria can grow was supposed to depend on fetch. These results suggest that buoyancy frequency be an effective index for planning and operating artificial destratification systems for preventing water bloom.

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We have conducted research on non-linear analysis for concrete dams using the smeared crack model. Efforts to verify applicability and accuracy of such numerical analyses for concrete dams have been made through simulations for actual damages of existing concrete dams due to large earthquakes. But, a more quantitative evaluation of the cracking process of concrete dams using crack analysis is needed in order to use such analytical method to estimate the limit state of concrete dams against large earthquakes. In the present study, we conducted shaking table tests on pillar-shaped unreinforced concrete specimens to investigate the effect of cracks on the dynamic behavior of concrete structures. The results showed that as tensile fracture progresses, the first resonant frequency of the specimen lowers and the damping increases. We simulated vibration tests by non-linear dynamic analysis based on the smeared crack model. Based on a comparison of the test results and numerical simulation, we discuss how to set parameters for numerical simulation such as the tension softening curve and damping ratio, to simulate the cracking behavior of unreinforced concrete structures such as concrete dams.

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