Wataru Yoshida
Research on temporal change of bathymetry caused by disposition of soil dredged in Niigata west port
Tokuzou Hosoyamada
The Niigata West Port, which is located in the entrance of the Shinano river has played an important role for economical development of Niigata city. However, the Niigata West Port is getting shallower because of sediment transport in the Shinano river and its deposition in the river mouth. To maintain the function of the Niigata West port, dredging the riverbed is inevitable all the year round. The amount of total dredged mud in a year in the Niigata West Port is about 800,000 m3,and of which 650,000 m3 is dumped at the offshore of Shinano river mouth. Ocean disposal of wastes area has changed at the intervals of several years. This research is aimed to investigate the changes in bathymetry around the dump area due to wave or current conditions.
Bathymetry data observed by the ministry of land, infrastructure and transportation (milt) from 2001 to 2008 is used to have interpolated bathymetry data. Interpolation or extrapolation method is used to obtain rectangular grid point values of altitude, which data is sometimes refereed to as Digital Elevation Model (DEM). The number of grids are 650 and 400 for longshore or offshore direction respectively. Motion picture was made with temporal interpolation of observed DEMs. By comparing the shallowest depth, which means the minimum depth of the convex region by the dumping, the convex area gradually goes down to offshore and deep sea direction without any influences of surface wave and wave induced currents. The deformation corresponds to the diffusion phenomenon, which is often seen in real fields. By giving an appropriate diffusion coefficient, the diffusion equation is applicable to predict the tendency of deformation of sea bottom shape changes caused by the dumping of dredging in Niigata West Port
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