Recent changes in hydrodynamic characteristics of the Pearl River Delta during the flood period and associated underlying causes

Abstract

It is well-known that both human activities and river-tide dynamics are significant factors affecting the hydrodynamic process in estuarine and coastal regions. In this respect, it is considered that riverbed down-cutting exacerbated by human interventions (such as dam construction, sand excavation, and dredging for navigation) may exert dramatic changes in the hydrodynamic characteristics of the Pearl River Delta (PRD). In this study, changes in the rating curves of residual water level (RWL) versus residual water discharge (RWD) at upstream stations of the PRD are examined between three extreme floods (here termed as “986,” “056,” and “086,” respectively), in addition to variations in RWL along the West, North, and East Rivers. The results show a dramatic downshift of the rating curves (0.65–4.9 m) in “056” and “086”, compared with the case in “986”. Besides, the RWL along the three tributaries fell significantly at the same RWD and the maximum reduction in the RWL occurred in the East River. It is considered that the main reason for this occurrence could be contributed to uneven deepening of river channels induced by uncontrolled and disorderly human activities. In addition, the decrease in RWL was more significant in the upper reaches than that in the lower reaches, which reduced the RWL slope and enhanced the PRD tidal dynamics. However, compared with the case in “056,” the rating curves in “086” are seen to shift up slightly (0.11–0.29 m) and the RWL increased in upstream parts but decreased in downstream parts in the West and North Rivers. This phenomenon can be attributed to the impacts of river-tide dynamics: river flow plays an important role upstream, and the flood wave in “086” delivered more water volume into the PRD for the same range of RWD and raised the RWL, whereas tidal dynamics contributed considerably to the effects downstream and the small tidal range in “086” lowered the RWL. It is anticipated that these results can be used as scientific guidelines for general water management and particularly for flood control in the PRD.