Coastal erosion is a severe problem elsewhere along the Japanese island, and efforts have been paid to cope the situation. For sophisticated management of coastal erosion, we must understand the spatial and temporal distribution of sediment fluxes, however, this item is usually very difficult to observe directly. The alternative way to estimate this item is measurement of bottom topographies, and then assess the sediment flux indirectly using the continuity equation between temporal change of bottom elevation and divergence of sediment flux. In this article, estimation of coastal sediment transport in the field is discussed, and then an attempt to estimate the sediment motion at the river mouth is introduced.

The variabilities of multiple bar system have been investigated in inter-annual time scale based on long-term field surveys. The field sites include Ishikawa Coast and Chirihama Coast facing the Sea of Japan. On both sites, large scale sandbar system has developed and the morphological variabilities are characterized by cyclic and systematic migration of multiple bars. On Ishikawa Coast, representative spatial patterns during individual cycle are analyzed to describe the three-dimensional morphological evolutions. Considerable changes in plan shape are observed such as quasi-regular crescentic patterns, parallel alignment of oblique bars, disconnection and realignment of bars. In contrast, bar migration on Chirihama Coast is quasi two-dimensional. The transition of the multiple sandbar systems is well reproduced by an empirical parametric model.

This manuscript demonstrated the characteristics of morphological change in Shichiri-mihama Ida coast, located in the southern part of Mie prefecture, by means of discriminant analysis based on shoreline change characteristics analyzed by network camera and wave data, and SfM/MVS analysis using UAV. Additionally, the correlation between the run-up height and the morphological change was discussed. As a result, discriminant analysis showed the usefulness of estimating advance, retrogression and stay events of shoreline behind artificial reefs at Ida beach. In the results of SfM/MVS analysis, the effectiveness of artificial reefs installed in Ida beach to reduce erosion behind artificial reefs, while it was confirmed that the function of artificial reefs to decline erosion was decreased by the long period waves with a significant wave period more than 13s. The total volume of Ida coast has increased due to the recently implemented beach nourishment. However, because the large beach nourishment material makes the foreshore slope of the Ida coast steep which is possible to accelerate beach erosion, the necessity of ongoing monitoring was suggested. Finally, the possibility to predict the maximum altitude of morphological change in Ida coast foreshores from the calculation of the run-up height by considering the wave direction of the wave after passing through the artificial reef was confirmed.

At the Great East Japan Earthquake of 2011, coastal structures were weakened by ground scouring and the consequent loss of the wave resistance function led to large scale damage. As this could seriously affect the economy of a country, urgent measures need to be taken to minimize the damage. In addition, floods arising from frequent heavy rains cause water levels to rise and prolonged high water levels lead to riverbed fluctuations, erosion, and destruction of river levees, and erosion due to overflow. In studies on the scouring phenomenon, tractive force has been widely used for evaluation. Evaluation by tractive force is done from a microscopic viewpoint, focusing on the balance between the shear force generated by the fluid on the ground surface and the effective weight of a soil particle in the outermost ground layer. However, when we consider the scouring phenomena that occurs around structures and on account of overtopping, the scale of scouring is such that it cannot be explained merely from the viewpoint of tractive force. Moreover, it has been pointed out in recent studies that the effect of fluid force does not only to affect the ground surface, but also causes stress changes inside the ground, thereby promoting scouring. Therefore, besides the microscopic view, it is necessary to elucidate the phenomena regarding the meso-scale of soil elements and to consider a wide range of perspectives of the macro scale of structures. Therefore, this paper demonstrates some of the findings from our research on the scour phenomenon focusing on soil-fluid interaction in multiple scales.

This study has experimentally investigated dense phase pneumatic conveying in a horizontal rectangular channel by fluidizing air. The powder was glass beads of the Geldart B particle, with mean particle diameter of 118μm, particle density of 2623kg/m³ and minimum fluidizing velocity of 12.3mm/s. Fluidizing velocities to the bottoms of powder discharge vessel and horizontal channel changed against minimum fluidizing velocity. The result showed that steady powder conveying achieved when height and pressure of powder bed at discharge vessel maintained the constant value. Mass flow rate of powder increased rapidly and reached the constant when fluidizing velocity at the bottom of a horizontal channel exceeded minimum fluidizing velocity. Solid loading ratio also increased with increasing fluidizing velocity, and took a maximum value. We found that powder conveying by fluidizing air realize high dense pneumatic transportation. In addition, we revealed that air pressures at powder discharge vessel and horizontal channel greatly influenced to mass flow rate.