Impacts of large-scale estuarine engineering projects on recent morphological evolution processes of the Yangtze Estuary
Abstract
Impacts of local human interventions on morphodynamics of large river deltas are insufficiently understood, especially superimposed upon delta erosion due to diminishing sediment supplies. The densely populated Yangtze Estuary in China is increasingly influenced by large-scale estuarine engineering projects in the recent two decades and thereby provides a useful example to address this issue. This work investigates the morphological impacts of the Deepwater Navigation Channel Project (DNCP) including dikes and groynes implemented in 1997-2010 on the mouth bar area of the Yangtze Estuary through morphological evolution analysis and process-based modeling approach (Delft3D). The seaward portion of the mouth bar area, defined as the study area for calculation of sediment volume change, converted from net accretion to net erosion during 1997-2013 primarily due to river sediment reduction. However, the East Hengsha Shoal (EHS) showed abnormal accretion in the same period. The accretion-erosion conversion occurred around the year 2007 and is largely contributed by two erosion zones at the northern and southern subaqueous delta, respectively. Hydrodynamic simulations indicate that the training walls result in weaker tidal flow and longer slack period at the EHS and stronger tidal flow at the southern erosion zone. Subsequently, morphological modeling demonstrates that the training walls enhance accretion at the EHS, which is mainly attribute to the downstream half of the north dike. This can be verified by the consistent period (2002-2004) of the dike extension to the present location and accretion peak of the EHS. Morphological modeling also indicates that the downstream half of the north dike enhanced erosion at the southern erosion zone, which can partly explain the gradual increase in the erosion volume of both erosion zones after 2004. Under large-scale estuarine engineering projects, the Yangtze subaqueous delta is accelerating to approach morphodynamic equilibrium. The timescale to the erosion limit and sustainable estuarine management merit further systematic research.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP23C2317L
- Keywords:
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- 0442 Estuarine and nearshore processes;
- BIOGEOSCIENCESDE: 1625 Geomorphology and weathering;
- GLOBAL CHANGEDE: 1641 Sea level change;
- GLOBAL CHANGEDE: 3020 Littoral processes;
- MARINE GEOLOGY AND GEOPHYSICS