Impact of sand excavation and waterway regulation on hydrodynamics of Pearl River networks

The established mathematical model for hydrodynamics of Pearl River networks is applied to numerically study the flow under the conditions of the topographic measured in 1990 and 2005 respectively. It is found that the water levels of the hydrological stations in the river networks decrease obviously in this period due to mankind activities including high intensity sand excavation and waterway regulation.The water level at the Sixianjiao Station which is the important control node of the river networks reduces by 2.68m during the flood with the probability of 0.01.Owing to the increase of channel volume the tidal dynamics of the river networks is enhanced,so that the annual tidal difference increases from 0.35m to 0.53m.As a result of the intensive change of river cross section the discharge in the river networks and river mouths is redistributed.The discharge of Hongqi River Mouth and Modao River Mouth increases significantly,but the discharge of other six river mouths decreases.The change of internal hydrodynamics of the river networks also induces the saline intrusion problem happened in the recent years.