SAND ACCUMULATION IN WAVE-SHELTER ZONE OF OHARAI PORT AND CHANGE IN GRAIN SIZE OF SEABED MATERIALS ON NEARBY COAST

Takeo Matsu-ura, Takaai Uda, Takayuki Kumada, Michio Sumiya

Abstract


Beach changes around Oharai Port facing the Pacific Ocean were investigated using bathymetric survey data collected over 25 years between 1979 and 2004. Between the south and offshore breakwaters of Oharai Port, 1.50×106 m3 of fine sand was deposited in this period, i.e., at an annual rate of 6.0×104 m3/yr, which was originally supplied from the Naka River 3 km north of the port. Also in the wave-shelter zone of the offshore breakwater south of the port, 7.0×106 m3 of fine sand was deposited between 1979 and 2004 at an annual rate of 2.8×105 m3/yr, which was transported by the northward longshore sand transport induced from outside to inside the wave-shelter zone of the offshore breakwater, resulting in severe beach erosion on the south coast outside the wave-shelter zone. Taking into consideration the fact that sand transport to the Kashimanada coast is now completely obstructed by the port breakwaters, sand bypassing and sand back passing to the coast from the sand deposition zone of Oharai Port are required.

Keywords


sand bypassing; sand back passing; sand deposition in the navigation channel; longshore sand transport; sediment supply from river

References


Kumada, T., T. Uda and M. Serizawa. 2007. Quantitative evaluation of controlling effect of headland on longshore sand transport using model for predicting changes in contour lines and grain size, Coastal Sediments '07, ASCE, 2446-2459.

Mimura, N. and H. Kato. 1991. Topographic responses to the construction of large port structure on Oharai coast, Coastal Sediments '91, ASCE, 2292-2306.

Nagayama, H., T. Uda, T. Matsu-ura and T. Kumada. 2008. Prediction of bathymetric and grain size changes around port subject to active supply of sand from large river, Proc. 31 st ICCE, 2110-2122.

Uda, T. 2009. Beach erosion arising from anthropogenic factors, Proc. Coastal Dynamics 2009, Keynote 1, 1-17.

Uda, T. 2010. Japan's Beach Erosion - Reality and Future Measures, World Scientific, 418 pp.


Full Text: PDF

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.