Decadal variations in the erosion/deposition pattern of the Hangzhou Bay and their mechanism in recent 50 a

Decadal variations in the erosion/deposition pattern of the Hangzhou Bay and their physical mechanism in recent years have been studied based on the bathymetrical data in 1959, 2003 and 2010, and historical changes of sediment supply from the Changjiang River and erosion/deposition in Qiantang estuary. The results show that (1) the upstream of Hangzhou Bay have been obviously deposited since 1959, and the deposition is featured by a developing trend toward downstream; (2) local bathymetry have been adjusted in the last half century, some small-scale shoal-channel systems have disappeared and the northern bank of the bay mouth have been been eroded since 2003 while it was deposited before 2003; (3) during 1959-2003 and 2003-2010, the annually-averaged sediments deposited in Hangzhou Bay are 0.91×10⁸ and 1.66×10⁸ m³, respectively, and the corresponding deposition rates are0.2 and 9.3 mm/a; (4) the effects of the dramatic reduction of sediment supply from Changjiang River have been not obvious for the whole Qiantang Estuary, i.e. from the Hangzhou Bay mouth to Zakou section, furthermore, the annually-averaged deposition rate after 2003 is a little more than that before 2003. This is probably caused by the land reclamation of the Qiantang Estuary in the past. The erosion/deposition pattern of the Hangzhou Bay in recent 50 a is a result of morphological response of both large and small river basin-estuary systems to human activities.