Regarding to dam sedimentation, researches have been mainly done on the configuration and the quantity of sediment from the viewpoint of the decrease of reservoir capacity. The systematical study including the quality of dam sediment is much more important from the viewpoint of the effective sediment utilization and the total sediment management. In this paper, we examined the data obtained from the boring investigation on reservoirs conducted by MLIT, paying specially attention to the containing rate of small-size particles which is very important for sediment utilization, and clarified the longitudinal and vertical properties of dam sediment. Also, consideration was made on how to use dam sediment including the supply material to river.

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In Aono dam reservoir, destratification operation was stopped for one month during the summer in 1991 to examine its effect on reservoir water quality. As a result, after the suspension of the circulation, a rapid development of anaerobic region below the middle depth was observed for 5 weeks. The lack of dissolved oxygen at the hypolimnion accelerated the release of nutrients from bottom sediments. After resuming the operation, it mixed nutrient rich bottom water with surface water causing the rapid phytoplankton growth in surface water for a couple days. From these evidences, it was revealed that the circulation system in Aono dam reservoir was strong enough to improve the dissolved oxygen concentration at the bottom; however it might also mix bottom water containing high concentration nutrients with the surface water.

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Dam foundations with good geological conditions are recently decreasing in number, and cut slopes become huge. Therefore, the establishment of the rational design method of cut slopes is required. We made investigation on profiles and design methods of cut slopes at dam sites, in order to acquire basic information for the purpose of the establishment of the rational design method of huge cut slopes. Stability analysis was also performed by plane failure method and distinct element method using the rock slope model, and fundamental study was performed about the characteristics of each analysis method.

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From the viewpoint of sustainable use of dam reservoir and conservation of river environment, it is expected to release the inflow sediment to a dam downstream. In order to release the sediment, hydraulic structures such as sediment flushing and bypassing facilities are generally used. And the estimation and countermeasures of abrasion should be serious subject for the design and management of those facilities. This paper proposes the method for estimating the quantities of local abrasion assuming those hydraulic structures will be constructed as concrete structures. The method is to estimate the prototype structure's abrasion from the hydraulic model test using easily damaged structure materials. This paper shows the fundamental idea of the method and clears the damage characteristics of wax and phenol resin, which is considered as usable to model materials. The application of this method also discussed including the remaining problems.

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