Interaction of Sandy Islands

The formation of land-tied islands as a result of the extension of a cuspate foreland, when waves were incident to several islands composed of sand from two opposite directions, was first investigated, taking a land-tied island offshore of Shodoshima Island in the Seto Inland Sea, Japan, as an example, and their topographic changes were predicted using the Type 5 BG model. Then, the interaction among multiple circular sandy islands on flat shallow seabed owing to waves was investigated, taking the islands in Hingham Bay near Boston Harbor as an example. On the basis of this example, topographic changes were also predicted using the Type 5 BG model

Formation of Sand Spit and Bay Barrier

The formation of a sand spit and bay barrier was predicted using the BG model, covering three topics: (1) formation of a bay barrier in flat shallow sea and merging of bay mouth sand spits (Section 2), (2) elongation of a sand spit on a seabed with different water depths (Section 3), and (3) deformation of a sandbar formed at the tip of the Futtsu cuspate foreland owing to a tsunami which propagated into Tokyo Bay after the Great East Japan Earthquake on March 11, 2011 (Section 4). The Type 5 BG model was employed in Section 2, and Type 3 BG model in Sections 3 and 4

Formation of Cuspate Foreland

The formation of a cuspate foreland when waves were incident from two opposite directions was investigated, taking a cuspate foreland extending at the northeast end of Graham Island in British Colombia of Canada and the cuspate forelands formed at the tip of Hon Bip Island north of Nha Trang, Vietnam, as the examples. The formation of such a cuspate foreland was predicted using the Type 4 BG model. Then, the development of multiple sand spits with rhythmic shapes in a shallow water body was investigated, taking the Sea of Azov in Russia as the example. Furthermore, the development of sand spits and cuspate forelands with rhythmic shapes was predicted, assuming that the waves were obliquely incident at angles of 60° relative to the direction normal to the shoreline or at angles of ±60° with probability p1:p2 = 0.50:0.50, 0.60:0.40, 0.65:0.35, 0.70:0.30, 0.75:0.25, and 0.80:0.20

Segmentation of Water Body and Lakeshore Changes behind an Island Owing to Wind Waves

In a slender water body with a large aspect ratio, the angle of wind waves relative to the direction normal to the shoreline may exceed 45°, resulting in the emergence of cuspate forelands and the segmentation of the water body. The BG model was used to predict the segmentation of a rectangular water body by wind waves when the probability of occurrence of the wind direction is given by a circular or elliptic distribution, and the segmentation of a rectangular water body into a circular or elliptic lake was predicted in each case. The segmentation of a shallow water body with a triangular or crescent shape was also predicted together with the prediction of lakeshore changes when a rocky or sandy island exists in a circular lake

Derivation of the BG Model

The BG model (a model for predicting 3D beach changes based on the Bagnold’s concept) was introduced, and the fundamental aspects of the model were explained. The BG model is based on the concepts such as (1) the contour line becomes orthogonal to the wave direction at any point at the final stage, (2) similarly, the local beach slope coincides with the equilibrium slope at any point, and (3) a restoring force is generated in response to the deviation from the statically stable condition, and sand transport occurs owing to this restoring force. The same concept has been employed in the contour-line-change model and N-line model. In these studies, the movement of certain contour lines was traced, but in the BG model, 3D beach changes were directly calculated

Prediction of Typical Beach Changes Owing to Human Activities

Beach changes related to human activities, such as the effect of construction of groynes and detached breakwaters on a coast with prevailing longshore sand transport, and offshore sand mining, which have engineering importance, were predicted using the Types 1 and 2 BG model. When a long port breakwater is extended, a large wave-shelter zone is formed and dominant longshore sand transport is induced from outside to inside the wave-shelter zone, resulting erosion outside the wave-shelter zone and accretion inside the wave-shelter zone. These beach changes were also predicted using the Type 2 BG model with the evaluation of the effect of a jetty extended at the port entrance to reduce sand deposition inside the port

Beach Changes on Coast Subject to Waves and Seaward or Shoreward Strong Currents

Beach changes on a coast subject to waves and seaward or shoreward strong currents were predicted using the Type 7 and 8 BG models. The formation of an ebb tidal delta subject to strong ebb tidal currents was studied first, taking the Imagire-guchi inlet connecting Lake Hamana with the Pacific Ocean as an example, and the long-term evolution of the tidal inlet was investigated using the bathymetric survey data. Then, the formation of a dynamically stable ebb tidal delta was predicted. Regarding the beach changes on a coast subject to waves and shoreward strong currents, the Type 8 was applied to the Kaike coast, where an artificial reef was constructed in place of a detached breakwater, resulting in the occurrence of strong shoreward currents over the artificial reef. A stable cuspate foreland behind a detached breakwater disappeared after the conversion of a detached breakwater into an artificial reef, suggesting that the artificial reef was less effective in sand deposition effect than the detached breakwater. Such beach changes were numerically predicted

Segmentation and Merging of Closed Water Bodies by Wind Waves

The segmentation and merging of elongated shallow water body with a large aspect ratio by wind waves were predicted using the Type 6 BG model. The deformation of a circular lake by wind waves was also studied when a straight seawall cutting a part of the water body was constructed in a lake for land reclamation, together with the investigation on the effect of the construction of detached breakwaters to the surrounding lakeshore. Finally, the formation of oriented lakes, groups of lake basins with a common long-axis orientation found in vast areas of the Arctic Coastal Plain, was predicted using the Type 6 BG model