We focused on hydrodynamic effects of the strip roughness on the surface-velocity divergence value to breakthrough about physical modeling of gas transfer mechanism in natural rivers. Accurate PIV measurements were conducted in a computer-controlled laboratory flume varying water discharge and roughness spacing, systematically, in order to obtain the space and time distributions of surface velocity divergence, turbulent kinetic energy and dissipation rate. Finally, a new practical model to predict the surface velocity divergence could be proposed successfully considering turbulence micro scales.

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 The tsunami run-up in the Kamaishi city caused by the 2011 off the Pacific coast of Tohoku Earthquake was simulated numerically by the 2-D shallow water model with fine grids resolving the roads and buildings. Additionally, a new semipermeable building model was conducted to considering the water volume flooded into the buildings. Compared with the ordinary model which considers the effect of buildings by adjusting the Manning's roughness coefficient, the maximum water levels in our model has higher correlation with the tsunami traces. In the coastal area, our calculations gave time series of water depth more consistent with the observation by the digital photo analysis. It means that the numerical accuracy gets improved by considering the collapse of buildings. In addition, it is shown that this model can estimate the tsunami time travel more reasonably than the ordinary model.

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 A model selection method is discussed for non-stationary hydrologic frequency models introducing time dependent parameters. For nested models, the likelihood ratio test is commonly used to choose an appropriate non-stationary hydrologic frequency model. The method, however, cannot be used to select a model among non-nested models. In this study, the Takeuchi information criterion, TIC and the Akaike information criterion, AIC are analytically confirmed for model selection criteria for non-stationary sequences. Then, non-stationary hydrologic frequency models with time dependent parameters, a non-stationary GEV model, a non-stationary Gumbel model, a non-stationary SQRT-ET model and a non-stationary lognormal model are applied to the observed annual maximum daily rainfall series in Japan and the best model are selected to examine the change of the annual maximum series. The non-stationary four models are also applied to GCM rainfall time series to examine future change of extreme rainfall intensity.

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 Appearance of blue-green-algae blooms in summer is still one of the serious water quality problems in Sagami Lake, Kanagawa, Japan, although several countermeasures have been implemented to mitigate it. Since the control of water discharge for hydropower generation is now considered as one of the possible measures, we tried to understand the difference in circulation patterns in the lake during both durations of operating and non-operating water discharge. Field data for currents and water temperature were collected in August, 2012. From the results, we found that during the period operating discharge, water flows into the lower layer following the meandering bathymetry. On the other hand, during the non-operation period, though overall currents become weak, adverse currents are observed in the upper layer of the upstream part of the lake.

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