| Sedimentation is an important problem that should be overcome when we utilize a reservoir for a long term. In addition, in recent years, to cope with problems such as river bed environment change downstream from dams, sea shore erosion and so on, it has been necessary to restore the continuity of sediment transport in rivers.Physical changes of a down stream river environment due to a dam are: river bed degradation (bedrock exposure), fixed river channel, armor coating (coarsening of bed material), decrease of the sediment supply volume, hydrological regime smoothing (tractive force decrease, decrease of disturbance due to peak flow rate decrease), reduction of dynamics of the rapids and pools in rivers and so on. We believe that supplying sediment properly from a reservoir may improve riverbed environments.Sedimentation countermeasures such as excavation (with sediment trap dams), dredging, sediment discharge facility, sediment bypass system, and placing sediment downstream from dams have already been carried out with constant effects. However, we think that problems regarding cost, application conditions, quantity and timing of the sediment supply must be overcome to apply these to many reservoirs. Therefore research and development of a new sediment supply technique (sediment removal technique) have advanced in various sectors. The authors have also developed two new techniques.In this thesis, we present the state of sedimentation countermeasures, sediment supply trails, and new technology development trends related to Japanese dam reservoirs, and indicate the future prospects for supplying sediment from dam reservoirs. |
