Linking the infilling of the North Branch in the Changjiang (Yangtze) estuary to anthropogenic activities from 1958 to 2013
Many tidally-dominated estuaries of theworld are experiencing variations in bottomtopography due to changes in natural forcings and intensive human activities. Here we focus on the morphological evolution of the North Branch (NB), a tidally-dominated distributary of the Changjiang estuary. Our analysis is based on long-term bathymetric and hydrological data collected between 1950 and 2010. The results show that mean water depth, channel volume below 0 m, and channel volume below −5 m have respectively decreased by 43%, 53% and 92% in the last 50 years. A reduction of the whole estuarine surface with aggradation in elongated tidal sand bars and erosion at themouth are the main morphological variations of the NB, while a decrease in channel volume below−5mdue to infilling is the second mode of morphological change.While the drastic decrease in sediment load from upstream is likely unrelated to the silting of the NB, local land reclamation along the banks is directly responsible for the reduction of estuarine surface area and related tidal prism. Between 1958 and 2013, enhanced flood-tide currents resulted in a large import of sediments from offshore into the NB, triggering a sustained decrease in channel volume below 0 m. It is argued that the recovery of the funnel-shaped configuration of the estuary by restoringmud flats over 0m, dredging the southern part of the estuary bend and forbidding land reclamation could prevent the silting of the NB, otherwise the NB will likely vanish in few decades.
Fig. 6. Erosion/accretion pattern in theNorth Branch identified by EOF analysis: contoured eigenvectors of the firstmode
Fig. 13. Land reclamation in the North Branch from 1958 to 2013.
Fig. 14. Flow dominance coefficient at two gauge stations in different years.
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