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When erosion occurs, sand beaches cannot maintain sufficient sand width, foreshore slopes become steeper due to frequent erosion effects, and beaches are trapped in a vicious cycle of vulnerability due to incident waves. Accordingly, beach nourishment can be used as a countermeasure to simultaneously minimize environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To address this problem, minimizing the period of renourishment is an economical alternative. In the present study, using the Tuvaluan coast with its cross-sectional gravel nourishment site, four different test cases were selected for the hydraulic model experiment aimed at discovering an effective nourishment strategy to determine effective alternative methods. Numerical simulations were performed to reproduce gravel nourishment; however, none of these models simultaneously simulated the sediment transport of gravel and sand. Thus, an artificial neural network, a deep learning model, was developed using hydraulic model experiments as training datasets to analyze the possibility of simultaneously accomplishing the sediment transport of sand and gravel and supplement the shortcomings of the numerical models.

This paper is concerned with the deposition of sediment due to dune forests (Nakatajima dune, Japan) and CC block system on a riverbank (Padma, Bangladesh). Measurements of sediment deposition were carried out at Nakatajima dune, Japan and at Padma riverbank, Rajshahi, Bangladesh using Global Positioning System (GPS). 2442 m3 sediment migrates each year to the East side of Nakatajima dune by wind and the edge of the dune develops about 6-7 m/year due to the existence of forests. Sedimentation rate is also greater in shallower mangrove areas. The trapped sediment height varies from 8.0 to 10.0 cm in the mangrove-lined bank. Mangrove forests help to trap 25% more sedimentation at low tide than at high tide. On the other hand, only for setting up the CC block and groynes along the bank, the sedimentation rate is observed almost twice than that of the previous year. An analysis shows that there is a similarity of sedimentation among dune, beach forests, mangrove forests and CC blocks. [ABSTRACT FROM AUTHOR]

Hamanako is an economically and culturally important tidal lake on the Pacific coast of Honshu, Japan. Between 1954 and 1973, entrance works were constructed to regulate the channel to the lake. In a previous paper, the tidal records from Maisaka just inside the lake, prior to regulation, were analyzed to explain the responses of the lake to the ocean tide and other water level changes. The present paper compares water level responses with those following regulation of the entrance. The principal differences are that at Maisaka the tidal range increased up to 1965, following the first stages of regulation, but it has been constant since then. In the inner part of the lake, regulation has increased the tidal range but reduced its variability and has reduced the mean water level in the lake. The southern sand shoal divides the lake into two tidal basins, with Maisaka lying in the smaller outer basin. Studies of the inner basin have shown that its tidal range continues to increase. A hydrodynamic model has been used to show that this increase is primarily due to scouring of the inner channel through the southern shoal. The model has also shown that the constancy of the Maisaka tidal amplitude since 1965 is not a static equilibrium, but is a balance between the effects of the outer entrance channel scouring and increasing the Maisaka tide, offset by the inner channel scouring and reducing the Maisaka tide. [ABSTRACT FROM AUTHOR]

The study examined the summertime behavior of phosphorus (P) and estimated P fluxes in the Inohana Lake Estuary, Shizuoka, Japan through a field observation conducted in the summer of 2007 and a box model approach. The sedimentation flux of P was significantly correlated with the overlying chlorophyll-a concentration. The box model provided a good estimate of the summer-averaged water flux. The P mass balance method yielded the release flux of P, which approximated the observed value. For the P exchange between the Inohana Lake Estuary and Hamana Bay, on the net flux, particulate P flows out into Hamana Bay through the upper layer, while dissolved P (phosphate P) flows into the Inohana Lake Estuary through the lower layer. For the P exchange between the upper and lower layers, the upward transport of P from the lower layer was more than 10 (~100) times greater than the downward transport of P. The results showed that P accumulates in the bottom sediment during the summer. This study indicates the possibility that the P input from Hamana Bay is dominant over the river P input in summer season with significant density stratification. [ABSTRACT FROM AUTHOR]