新潟海岸の大規模海浜過程と海岸侵食制御に関する研究

Abstract

Most of Japan's erosive beaches locate in the river mouth delta in which beach protection has to be considered from the points of view such as: (I) beach change is in the processes of river mouth delta deformation, and (ii) finding the solution of stable beach under river mouth processes.The spatial scale of river mouth is from ten to hundred kilometers and strongly depends on the river's capacity of sediment supply.Based on these view-points, erosion control problem of Niigata coast is dealt in this paper.After construction of the Okozu diversion channel from the Shinano-gawa river in 1922 to control river flooding, the river delta reduction of Shinano-gawa river started.Severe subsidence due to oil and natural liquid gas mining accelerated beach erosion as well. Various river developments have been conducted and a lot of countermeasures against coastal erosion, such as revetment detached breakwaters and groins, have continuously been constructed since around 1935.First longshore sediment transport rate is investigated by finding the representative wave condition for long-term beach changes. Secondly the erosion control measures are proposed by considering longshore sediment budget and beach stabilization.By considering total balance of longshore sediment transport, dynamically stable pocket beaches are calculated using the equation of equilibrium bay.Numerical simulation of beach response to abnormal storm wave conditions was also performed to test the stability of three types of nourished beaches.It was confirmed that no significant out-going sediment from the pocket beach was observed in the results of numerical simulation of three dimensional beach changes.