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The roles of forest along the river bank have been noted from the view point of the river environment and flood disaster. Bed load transport and sediment deposition are experimentally examined in an open channel with cylinders installed across the whole channel width in their multiple rows. Cylinders were placed in stagger with their equal spacing on the bed.The transport rate of bed load was measured on the movable bed. The bed-load transport rate was found less than that in an open channel without cylinders. Effcetive friction velocity was found from the comparison of the measurement of bed-load transport rate with a transport rate equation. The transport rate of bed load and the non-dimensional average velocity decrease with the arrangement density of cylinders.Sediment deposition profiles were also measured. In the case of larger density of cylinder arrangement, sediment deposition occurs in the upper stream reach, while, in the case of smaller density, sediment deposition occurs in the downstream reach. The comparison of the calculation and the experiments shows good agreement.

TASAKIWe can distinguish four main types of sediment transport and their two itermediate types on movable bed in a steep open channel; those are bed and suspended load types, debris and mud flow types , and intermediate types between bed load and debris flow types. The flow model for hyperconcentrated sand-water mixtures proposed by Hirano and Hashimoto(1995 , 1997) can be applied to all types of flows with sediment transport in a steep open channel. The flow model consists of granular and inertial layers; the intergranular stresses play major role in the former layer and inertial forces in the latter layer. On the basis of the flow model, sediment discharge formulas have been derived by Hirano and Hashimoto (1996, 1998). In the present study the sediment discharge formulas are compared with the experimental results and also with the other formulas. The calculation of sediment discharge formulas derived by Hirano and Hashimoto (1996, 1998) shows good agreement with experimental results .

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There occurs significant gully erosion and sediment runoff by rainfall on the slope of the Mt. Unzen Fugendake. This causes a large increase of bed elevation and sometimes great damage to the houses in the downstream area of the slope. In order to prevent the disasters, the prediction of the runoff of sediment and water is an important problem. It is necessary to understand the process of erosion and variation of a gully to estimate the runoff of sediment and water from the mountain slope .The purpose of this study is to investigate discharge of sediment and water,sediment concentration,bank erosion and bed variation in the lateral erodible straight channel at steep slope .From the experiments it is found that bank erosion causes an increase in discharge of sediment and water and sediment concentration in the channel.

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