Human-induced hydrological changes in the river network of the Pearl River Delta, South China

With the rapid socio-economic development and urbanization, dramatic changes of the hydrological characteristics have taken place in the river network of the Pearl River Delta (PRD) over the past decade. These changes can be mainly attributed to the combined effects of the following human activities: sand dredging in the river, reclamation of former flood-afflicted areas, connection of dykes, construction of numerous bridges, docks and sluices along the river and irrational regulation of water locks. Human activities, along with strong riverbed scouring and sea level rise, respectively, give rise to riverbed degradation and stage reduction in the upper river reaches of the Delta, but sedimentation and tidal backwater resistance in the river mouths. Corresponding to the stage changes, the stage-discharge relationship has been substantially modified, as evidenced by over 2-m drop of stage for the same amount of discharge in some river sections. The ratio of flow partition in river network of the PRD has also been changing continuously in recent years. This is an excellent indication of an increasingly larger portion of flow discharging from the Xijiang River channels into the river network of the Delta, which was found to be the main cause making the inner part of the PRD more and more vulnerable to flood in recent years.