REASON OF FIXATION OF MOUTH OF A SMALL RIVER BEHIND NATURAL REEF

The mechanism by which the mouth of a small river is stably fixed in the wave-shelter zone behind an offshore reef composed of natural rocks was studied, taking a small river flowing into the Moriya coast together with two other small rivers as examples. The beach topography around the river mouth and the shape of the stream behind the reef were measured on this coast, and the wave height distribution around the reef was calculated using the angular spreading method, and the reason why the river mouth is stably fixed at this location was considered. Furthermore, the numerical simulation of beach changes using the BG model when an offshore breakwater was installed as a model of a natural reef was carried out to study the longshore change in the berm height. The primary cause for the fixation of a river mouth behind a reef was found to be the decrease in wave height behind the reef, which in turn decreases in the berm height.

Turbulent Distance of Partially Coherent Hollow Gaussian Beams

For partially coherent hollow Gaussian beam (HGB), the turbulent distance, in which all of the spatial and angular spreading and the beam propagation factor increasing due to turbulence can be neglected, has been investigated in detail. It is shown that the turbulent distance of partial coherent HGBs increases with increasing beam order and wavelength, and decreasing turbulent parameter and coherent parameter. With increasing waist width, the turbulent distance first increases and then decreases. Furthermore, the turbulent distance of a HGB is much larger than that of the corresponding Gaussian Schell-model (GSM) beam when choosing the appropriate value of the waist width, implying that a HGB may be more appropriate to be used in optical communication links than a GSM beam.