Author(s): Kazunori Wada
Linked Author(s):
Keywords: Coastal Erosion; Headland; Sediment Control; Wave Energy
Abstract: The present paper will share the experiences on wise management of coast and river basin through the study of management of Tone River basin and Kashima coast. The Tone River basin is the largest basin in Japan. About 30 millions people live in Tokyo and the surrounding five prefectures located within the basin. For several decades, due to the reduction of sand supply from the Tone River; and moreover, the prevention of alongshore sand drift by gigantic Kashima Port, beach erosion has been a serious problem in Kashima coast. The invasion of the ocean reaches as much as 100m into the land. To regain the sand beach and prevent the coast from erosion, total of 40 artificial headlands are scheduled to construct along the coast of Kashima, about 97km in length. Started in 1985, 32headlands have been completed by the end of 2003. A remarkable effect of suppressing the invasion has already become visible in the coast where the headlands were completed. The beach restored by the headland has an arch shape by the effect of refraction and diffraction of the wave, and becomes to stabilize. Artificial headlands divide the shoreline moderately; stabilize discrete lengths of the dune face while allowing the intervening stretches to erode naturally, forming an increasingly embayed shoreline. As the shoreline becomes more indented so the wave energy will be dissipated over a longer frontage and ultimately a more stable planned shoreline can develop. As a result, sandy beach stored between the artificial headlands (so-called the pocket beach) are hardly to be eroded and can be stabilized for long term. With moderate construction cost but low maintenance, artificial headland is profitable in comparison with other conventional coastal protection methods. The headlands protection method allows natural processes to continue elsewhere, and protects the beach effectively. This not only improves durability against high waves and erosion, but also enhances scenic and recreational aspects. The content of the present paper also includes the beach erosion disasters, the sediment transport and the coastal geomorphology. Lastly, the paper will summarize with proposals for wise management of river basin.
Year: 2007