Papers by Yasuyuki Nakagawa
Lecture notes in civil engineering, 2023
The present study focused on the siltation process at the navigation channel in the Port of Niiga... more The present study focused on the siltation process at the navigation channel in the Port of Niigata, Japan. A part of the port is located at the mouth of the Shinano River, which is the longest one in the country. Due to the discharged sediments through the river and their deposition in the port area, frequent dredging works are required for the safety navigations in the waterway and turning basins. The purpose of the present study is to get a better understanding of the specific features of the sedimentary process in the target area for the consideration of any appropriate countermeasures for the optimization of the dredging works. 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 complicated estuarine hydraulic conditions and several field measurements have been carried out, including current measurements, bathymetric surveys by acoustic soundings with a narrow multibeam sonar system.
SSRN Electronic Journal, 2022
Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), 2018
Coastal Engineering Journal, 1998
A new computational scheme for calculating the nonlinear energy transfer in finite-depth gravity ... more A new computational scheme for calculating the nonlinear energy transfer in finite-depth gravity wave spectra has been developed by extending the methods established by Masuda (1980) and Komatsu et...
Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), 2015
Science of The Total Environment
Hypoxia is a long-standing environmental problem in coastal areas worldwide, but technical and ec... more Hypoxia is a long-standing environmental problem in coastal areas worldwide, but technical and economic difficulties impede accurate and continuous spatiotemporal monitoring. This study aims to monitor seasonal hypoxia dynamics at high-resolution by developing a novel capacitive potentiometric sensor. The underlying hypothesis of this study was that (1) the capacitive carbon electrode charges redox energy and creates an overvoltage; (2) the overvoltage reflects the redox energy as an amplified signal. A viability of the capacitive potentiometric sensor for seasonal hypoxia was investigated from summer to autumn in Fukuyama inner bay, Japan. The study area was a brackish water with strong stratification of upper fresh water and lower saline water. In the water surface, which is a redox-equilibrium environment, the capacitive potential increased to 0.7 V with overvoltage, which corresponds to amplifying the redox energy of dissolved oxygen by 35 times. In contrast, in the bottom layer, the capacitive potential responded in a Nernstian manner, confirming that diffusion of hydrogen sulfide was the direct cause of the hypoxic water mass in the bottom of the study area. The vertical discontinuity layer of the redox reactions was defined as 0.05 V of the capacitive potential. This threshold value intuitively illustrates the spatiotemporal dynamics of the seasonal hypoxia. A principal component analysis confirmed that dissolved oxygen concentration was a major determinant of the capacitive potential. Furthermore, this novel potentiometric sensor overcomes the limitations of conventional redox potential sensors, which fail to capture weakly poised redox couples. The capacitive potential exhibited that the stratification protected environments for photosynthesis (surface water temperature and aerobic condition), thus regularly supplies dissolved oxygen to seabed with tide and suppressed full-depth hypoxia. In conclusion, the capacitive potential provides spatiotemporal information on the chemical activity of dissolved oxygen, which is a novel approach to elucidate the mechanisms of hypoxia dynamics.
PROCEEDINGS OF CIVIL ENGINEERING IN THE OCEAN, 2004
Littoral landform, temperature and moisture condition are studied in relation to the habitat of C... more Littoral landform, temperature and moisture condition are studied in relation to the habitat of Cicindela lewisi juveniles at Okinosu beach, Tokushima prefecture, where artificial beach is planned for alternate its habitat. This paper describes environmental condition of existing juveniles habitat which locate narrow line near the coastline of HWL, and proposes required environmental targets to make alternate habitat in the artificial beach and key terms of reference to confirm juveniles ecesis in the process of adaptive management.
Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 2019
Soils and Foundations, 2020
This paper presents a formula to estimate the stable weight of a rubble mound for breakwaters, co... more This paper presents a formula to estimate the stable weight of a rubble mound for breakwaters, considering the tsunami-induced overflow and seepage flow, based on the theoretical force balance among the frictional resistance of the rubble mound, the tractive force of the water flow over the caisson to the rubble mound and the seepage force of the rubble mound through the breakwaters. A series of hydraulic model tests was conducted on the scale of 1/100 for the Kamaishi Harbor Mouth Breakwaters in order to confirm the effectiveness of the proposed formula. Using the test results, the stability of rubble mounds for breakwaters was evaluated from the geotechnical engineering and hydrodynamical points of view.
Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), 2021
Journal of Marine Science and Engineering, 2020
Long-term beach observation data for several decades are essential to validate beach morphodynami... more Long-term beach observation data for several decades are essential to validate beach morphodynamic models that are used to predict coastal responses to sea-level rise and wave climate changes. At the Hasaki coast, Japan, the beach profile has been measured for 34 years at a daily to weekly time interval. This beach morphological dataset is one of the longest and most high-frequency measurements of the beach morphological change worldwide. The profile data, with more than 6800 records, reflect short- to long-term beach morphological change, showing coastal dune development, foreshore morphological change and longshore bar movement. We investigated the temporal beach variability from the decadal and monthly variations in elevation. Extremely high waves and tidal anomalies from an extratropical cyclone caused a significant change in the long-term bar behavior and foreshore slope. The berm and bar variability were also affected by seasonal wave and water level variations. The variabilit...
Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering), 2020
The Journal of Japan Institute of Navigation, 2020
Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering), 2020
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Papers by Yasuyuki Nakagawa