Author(s): Chenjuan Jiang; Qingshu Yang; Caian Huang
Linked Author(s): Caian Huang
Keywords: Estuarine regulation project，Sand excavation; Morphological evolution; Modaomen Estuary
Abstract: Due to the estuarine regulation project mainly executed during 1983-1993, the Modaomen Estuary had extended to the sea significantly, inducing hydrodynamic changes and seaward extension of its deposition structure. Besides, sand excavation in the Modaomen channel and in the upstream river networks since 1980s directly resulted in the deepening of riverbed, hence the increase in tidal dynamics. In this paper, we investigate how these human interventions affected morphological changes of the Modaomen Estuary in recent decades. Morphological changes were assessed by analyzing digitized bathymetric data of this area during 1977-2005. In the inner estuary (river-dominated part), there was deposition on shoals and erosion in deep channel with bank-full water volume increased, and the riverbed evolved to be narrower and deeper during 1977-1999. It suggests that the effects of runoff on the bed-forming process increased due to human interventions, and the reconstruction of the bed by tide also induced the deepening of tough. In the central estuary (mixed-energy), the reclamation of western shoal resulted in the narrowing of the estuary by more than 30% and the significant deepening of the eastern main channel. Right after the regulation project, the central estuary experienced significant self-adjustment, with average depth of riverbed increased and the riverbed turned to be narrower and deeper, which suggests the intensification of the bed-forming process by runoff and tide. However, after 2000, there was still deposition on shoals and erosion in channels, but the water volume below 0 m isobaths was stable. In the outer estuary (marine-dominated part), extraoral mouth bar shifted seaward rapidly during 1994-2000, with significant extension both horizontally and vertically due to sediment accretion. Meanwhile, the 4 m isobaths turned to be straighter due to wave modification on the seabed. During 2000-2005, the channels in the mouth bar extended seaward by erosion, especially the eastern channel, but the mouth bar showed no obvious extension. The morphology of the estuary showed slight change during 2000-2005, demonstrating that the dramatic self-adjustment after regulation project was completed and the estuary has developed into a new stable state.
Year: 2013