For clarifying the possibility of forestation in gravel bed bars or islands, sediment load change index (SLI) has been proposed considering deposition and washout of fine sand during flood discharge is declined. The applicability of this index was validated in the middle stream reach of the Oppe River, the Arakawa River and the Kanna River. Before and after typhoons in 2007, 2011 2012 and 2013, field investigations were conducted on six gravel bars in four rivers. River flow was also analyzed by two-dimensional depth-averaged Reynolds equations, and SLI was calculated. In comparison with SLI and sand deposition situation on the observed gravel bars, SLI has been found to express well the sand deposition situation on most of observed gravel bars. However, when this method is applied to the gravel bar which has small relative height from low channel and long distance along the flow direction, SLI could not express well the actual deposition situation. The effect of the excavation of gravel bar was investigated at Honda location in the Arakawa River through SLI. The re-colonization of the grass-type vegetation can be confirmed at the location where SLI becomes higher due to the excavation. This result indicates SLI is a suitable index for evaluating the effectiveness of the excavation of the gravel bar.

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 A dynamic model for predicting the long term change of vegetated area in river was developed when the flood does not change the morphology of the gravel bar. In this simulation model, the expansion, destruction due to floods and regeneration of the plants were considered. Change of vegetation succession speed was included in relation to the tendency of fine sand deposition due to floods. For elucidating the characteristics of deposition of fine sand due to floods, deposition situation after 2007 and 2012 flood events were investigated on the two gravel bars in the middle stream of Arakawa River.
 The simulation model was developed on a gravel bar located near Kumagaya Ohashi (KU) and applied to a gravel bar located near Arakawa Ohashi (AR) for validating the change of vegetated area from 2000 to 2012. This model expressed the situation of vegetated area in 2012 within the reasonable limit. Especially, this model can be found to describe not only the expansion location of each vegetation but also the vegetated area of each vegetation by considering change of vegetation succession due to deposition of fine sand by floods.

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 The formation of oxygen-poor water and the occurrence of hydrogen sulfide in estuary are caused by the sludge which contains a lot of organic substance. In order to examine measures against the water environment problems caused by the sludge, it is necessary to estimate bottom shear stress which exert an influence on the behavior of bottom material. Based on our study, the bottom shear stress was estimated by the method of using the change of water level obtained by one-dimensional unsteady flow analysis and the density distribution obtained by field observation. The estimated bottom shear stress was validated by comparison with coefficient of eddy viscosity. An increase in the bottom shear stress during flood tide is caused that the tip of saline wedge passes through a cross section.

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