Hydrodynamic interactions between tide and runoff in the Luanhe Estuary in Bohai Sea, China: From aquaculture reclamation to restoration

Abstract

Tidal flat reclamation causes a series of negative consequences for the coast-estuary hydrodynamics and environment. This might lead to implementing the restoration of the reclaimed areas. However, the restoration induced hydrodynamics changes have not been comprehensively understood in estuaries. In this study, the hydrodynamic interactions between tide and runoff are investigated using a numerical modelling of the Luanhe River Estuary, China, a typical micro-tidal estuary just experienced the restoration from the densely covered reclamations. The focus of this study is on the changes of the tidal field, characteristics of tidal prism and asymmetry and evaluation of flood risk. The results indicate that the restoration has significantly decreased the flow velocity by as much as 60% in the estuarine river during flood season. In dry season, the interaction between runoff and tide will be enhanced with larger tidal velocity, longer tide intrusion and very tiny area with static water due to the restoration. The tidal prism has been significantly increased by more than twice in the dry season owing to the both enhancements in intrusion velocity and rising duration of the flooding tide. Also, the restoration has effectively dropped the flood water level and slow down current flow speed in the river channel. In conclusion, the restoration project is of great significance to reduce storm surge risk and to improve water quality. The restoration project provides an effective reference for the spatial arrangement of the aquaculture reclamation and primitive tidal flat, which is conducive to the efficient and coordinated utilization of coastal zones.