Beach erosion triggered by river mouth dredging as a measure against river mouth closure

On a pocket beach, the impact of the formation of the wave-shelter zone and the maintenance dredging of a river mouth reaches the entire pocket beach, and overall beach changes are triggered, devastating the natural environment. These topographic changes owing to anthropogenic factors took place at many coasts in Japan with the development of the coastal zone. We investigated this issue, taking the Haraoka and Tatara coasts in Chiba Prefecture as examples. Although several measures have been taken such as the sand back pass to mitigate the erosion, problems have not yet been solved. We discuss the reality and propose several measures to solve these problems

Topographic changes on Ajigura beach triggered by elongation of offshore breakwater

On Ajigaura Beach in Ibaraki Prefecture, Japan, severe beach erosion has occurred. Despite beach nourishment as a measure against beach erosion, wave run-up damage occurred in the south part of the beach where the foreshore was narrowed. The topographic changes of the beach were investigated on the basis of past aerial photographs and bathymetric survey data, and a numerical simulation using the BG model (a three-dimensional model for predicting beach changes based on Bagnold???s concept) was carried out. The measured and calculated results were in good agreement. It was concluded that the beach changes at Ajigaura Beach were triggered by northward longshore sand transport, which was induced by the wave-sheltering effect of the offshore breakwater

Essays on river mechanics

CER92-93-PYJ-5.Presented by the Graduate Students in CE 717 - River Mechanics (Spring 1993).Includes bibliographical references.April 1993