Redistribution of the Suspended Sediment at the Apex Bifurcation in the Pearl River Network, South China

Abstract

Zhang, W; Du, J; Zheng, J; Wei, X., and Zhu, Y. 2014. Redistribution of the suspended sediment at the apex bifurcation in the Pearl River network, South China. Bifurcations in tidal networks strongly control the distribution of flow and sediment flux over a river network system. These distributions are important in determining the fluvial sediment dispersal and transport from river networks to shorelines, thereby greatly affecting river channel, estuary, and coastal environments. Long-term observations of flow and suspended sediment division at the apex bifurcation of the Pearl River network indicate that there has obviously been more water and sediment transport into the North River network since the 1990s. Wavelet analyses of the sediment division at the apex bifurcation show that common spectral structures were dominated by annual fluctuations from 1959 to 2005. However, significant, intra-annual and annual fluctuations have been detected since the early 1990s, corresponding well with the abrupt changes in flow and sediment division. By analyzing the controlling factors (water discharge ratio ηL and suspended-sediment concentration ratio KS) of the suspended-sediment flux distribution in a braided river, we concluded that both the riverbed downcutting from intensive sand mining in the lower river and the lack of suspended-sediment supply because of dam construction in the upper river are primarily responsible for the sediment redistribution in the apex bifurcation of the Pearl River delta. Furthermore, the wavelet analysis indicates an energy growth in the signal of the suspended-sediment division ratio. The observed spectral composition was used to estimate the potential suspended-sediment division in the absence of human influences by removing the effect of that energy growth, which helped to explain the extent of the effect of intensive anthropogenic activities on the redistribution of suspended-sediment flux. The estimate indicates that there has been a decrease of 6.27 × 107 tons of suspended-sediment load flowing to the West River network for sediment redistribution at the apex bifurcation of the Pearl River delta between 1992 and 2005.