PIANC Smart Rivers 2022

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Abstract : *(250~1000 words)

The present study focused on the siltation process at the navigation channel in the Port of Niigata, Japan. Since a part of the port is located in the mouth of the Shinano River, which is the longest one in the country, continuous maintenance and developments have been historically required for the safety navigations in the water way and turning basins there. Due to the discharged sediments through the river and their deposition in the port area, annual dredging volume is approximately 800,000m3 in the recent years. Minimizing the dredging volume is crucial for the port operation, just same as any other ports in the world with the similar sedimentation problems.
The purpose of the present study is to get better understanding of the specific features of sedimentary process in the target area for the considerations of any appropriate countermeasures for the minimization of the dredging volume. In the present study, we especially focus on the sedimentation processes around the dredged navigation channel, which need frequent dredging to keep the planned depth from -5.5 to -12 m, under the complicate estuarine hydraulic conditions and several field measurements have been carried out, including bathymetric survey with acoustic soundings, in-situ bulk density for the fluid mud studies and current measurements.
As an example of the results of the field surveys, the paper will provide obtained data from the monitoring campaign during January and February in 2020, where a multi-beam sonar was used for the evaluation of the bathymetric change with the higher spatial resolution. In order to sedimentary information, core samples were taken at several points and analysed for the sediment parameters such as particle size and water contents. Furthermore, an in-situ bulk densimeter, Mud Bug of Hydramotion Ltd., was also applied to get information on the vertical profiles of mud density or the thickness of fluid mud layer near the bed.
Temporal change analysis of the bathymetry in the dredged channel between the surveys in 2020 shows slight deposition with the thickness of at most 20 cm on the bottom of the dredged channel, although rapid siltation over 1 m in thickness is also shown at the upstream steep slope or border between the dredged and non-dredging area even for the three weeks. According to the bottom sediment analysis, most of them are silt and clay but dead leaves and litters were also observed on the border slope area with the rapid siltation area.
The paper will further discuss and describe the characteristics of the sedimentation process in the study site, considering hydraulic aspects in the area under the stratified conditions, which is critical in the estuarine environment.

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