[H-CG28] [EE] デルタ（三角州）：複雑系への学際的アプローチ

[HCG28-P01] Impact of human activities on subaqueous topographic change in Lingding Bay of the Pearl River estuary, China during 1955–2013

*Ziyin Wu^1,2、Yoshiki Saito^3,4、Dineng Zhao²、Jieqiong Zhou²、Zhenyi Cao¹ (1.Key Laboratory of Submarine Geosciences and Second Institute Oceanography, State Oceanic Administration, Hangzhou 310012, China、2.School of Earth Sciences, Zhejiang University, Hangzhou 310028, China、3.Geological Survey of Japan, AIST. Central 7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan、4.Department of Natural Environmental Studies, Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8563, Japan)

キーワード：human activities, estuarine topography, Lingding Bay, Pearl River, evolution

Estuaries have been the site of intensive human activities during the past century. The decadal time-scale evolution of subaqueous topography in estuaries enables us to understand the effects of human activities on estuaries. From 1955 to 2010, land reclamation decreased the area of Lingding Bay by 10% (~170km²), and the water volume of Lingding Bay decreased by 615 × 10⁶ m³. This shows a net decrease of 11.2 × 10⁶ m³ a year, indicating that approximately 14.5 Mt/yr of sediment was deposited in Lingding Bay during that period. Before 1980, Lingding Bay was mainly governed by natural processes with slight net deposition, whereas after 1980 dredging in the bay and large port engineering projects changed the subaqueous topography by shallowing the shoals and deepening the troughs in the bay. Between 2012 and 2013, large-scale human activities including continuous dredging and a surge of sand excavation were found clearly with water depth changes of ±5 m/yr, far exceeding the magnitude of natural topographic evolution in Lingding Bay. Human activities such as reclamation, dredging, and navigation-channel projects remove about 8.4 Mt/yr of sediment from Lingding Bay, accounting for 29% of the sediment input to the bay, and these activities have increased recently.