Changjiang River delta sedimentation in response to catchment changes
Shu Gao
(Ministry of Education Key Laboratory for Coast and Island Development, Nanjing
University, Nanjing 210093)
shugao@nju.edu.cn
Abstract: The Changjiang system is important to the study of catchment-coast
interaction. The response of the sediment system of the Changjiang sub-aqueous delta
to the changes in river input is examined in the present contribution. Analyses of
sediment cores, tidal cycle measurements of current velocities and suspended
sediment concentrations, satellite imagery and historical records about bathymetric
changes and shoreline positions indicate that the accumulation rate over the
sub-aqueous delta has been decreasing in response to reduction of the sediment
discharge from the river. Remote sensing data for the last 30 years reveal a trend of
decrease of suspended sediment concentration in both the river channel and in the
estuarine waters. Likewise, deposition rates on the basis of Pb-210 and Cs-137
analysis of the cores also show a trend of reduction. Based upon a definition of
“sediment retention index”, which is a function of sediment discharge of the river and
the rate of sediment escape from the delta system, the deposition rate of the short
cores can be modeled. The results show a general agreement with the observed rates,
indicating that the change in the deposition pattern is indeed related to the reduction
of the river input. It is proposed that further reduction of the river input in the near
future, with the Three Gorges Dam being in full operation, there will be no further
growth of the Changjiang delta, which will modify the physical environment, material
cycling patterns and ecosystem dynamics of the region.
Keywords:
Catchment-coast
interaction;
suspended
sediment
deposition rates; sediment retention index; Changjiang delta
concentrations;