Hydraulic model tests and flume experiments for mountainous torrents and rivers have been conducted to clarify flow characteristics for many kinds of sediment movement modes such as mud flow, debris flow and so on. Especially, in case of mud flows and sediment laden flows with wide sediment grain size distribution, there are problems to be solved for not only similarity in experimental approach, but also flow model and constitutive relationship in numerical simulation.
In flume tests, coarse sediment particles can reproduce sediment erosion/deposition in those flow regimes, focusing on that locally spatial and time averaged bed variation is formed mainly by bedloads. However, it can be quite difficult to reproduce turbulent flow with fine sediment particles in model flume. In case of mud flows, modeling and treatments for muddy flow body which is liquid-phase are still now difficult and coarse sediment particles can be regarded as particles with small specific weight in comparison to sand. Additionally, in case of sediment laden flows with nonuniform sediment, it can be important to consider how to reproduce wide grain size distribution of sediment particles in model. It can be better that artificial material is used in place of sand particles based on Froude and dimensionless bed shear stress similarity to reproduce several sediment transport modes. In present study, the applicability of light and heavy artificial material for hydraulic experimental teats is examined using experimental data such as sediment flux concentration and flow resistance in flows over erodible bed.

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In Akita prefecture in Japan, two kinds of wooden erosion-control dams, which are Akita original, have been studied and developed from 2001. One of which is all wood type dam composed only wood members and lag screws and another is hybrid dam packed the thinned wood and gravels in the steel flexible frame, and total of thirty dams are already constructed in Akita prefecture as of 2011. However, since these dams cost are about two times high than concrete dam, as the next stage of studies and development, the researches of cost reduction type dams are advanced now. In all wood dam the costs of lag screw are six million yen per unit, if it is possible to change the lag screws to the cheap pin as round steel, it seems that the costs of a few million yen per unit can reduce. But it is has been understood that the combined stress occurred at the lag screws, it is difficult to adequately consider the different pins one per one. Therefore, in this study, we tried to the optimum design concerning the arrangements of pins by using FEM that can consider the complex combined stress. First, FEM analyses were carried out for the specimen used all lag screw and used all round steel, and the results as for vertical and horizontal displacements, the maximum quantity of pullout of each pin and the stress occurred at each pin and the wood members are compared. Based on these results, the cost reduction dam where the all lag screw on downstream side except the first tier changed round steels was designed. Finally, we conduct FEM for the cost reduction dam, it was shown that the specimen have safety rate 8 for the design load.

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The main part of a check dam installed in the Shigekurazawa, a tributary of the Tone River, was removed in November 2009. The dam was removed to restore the stream ecosystem and develop a new method and technology for stream conservation. Removal of a check dam in the ecological context was unique implementation in Japan. The stream is in the forest area of the Akaya Project, a project that has been conducted through discussion and collaboration among the Kanto Regional Forest Office, the Nature Conservation Society of Japan, and a council organized by the local people in order to recover the ecosystem of the area. The participants engaged in consultation with professionals regarding disaster prevention and specific ecological and engineering problems and designed a basic plan for engineering and monitoring based on the concept of adaptive management that was then executed by the Kanto Regional Forest Office. Forest conservation engineering conventionally focuses on disaster prevention; however, the current plan would give ecological contents in Japanese forest conservation plan and engineering.

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Rainfall-runoff, sediment production and flow-out in mountain watershed are simulated. Runoff is calculated from rainfall as kinematic wave. Sediment production and flow-out are calculated as an one dimensional model. This simulation model is a modified version of SERMOW for Sediment Runoff from a Mountain Watershed. It is named SERMOW-II. This model is applied to the observed rainfall, runoff and sediment measurement data for the Ashiaraidani basin. The model considers various types of sediment transport; from debris flow to bed load, although landslides on slopes are not considered. The model can explain the data well after adjusting the parameters. The influence of grain size distribution of the supplied sediment to flow-out sediment was examined with the model.

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