Dynamics of upstream saltwater intrusion driven by tidal river in coastal aquifers

Bo Zhang; Tianyuan Zheng; Xilai Zheng; Shiqiang Jiang; Min Cao; Marc Walther; Chunhui Lu

doi:10.1016/j.scitotenv.2023.162857

Dynamics of upstream saltwater intrusion driven by tidal river in coastal aquifers

Sci Total Environ. 2023 Jun 15:877:162857. doi: 10.1016/j.scitotenv.2023.162857. Epub 2023 Mar 15.

Authors

Bo Zhang¹, Tianyuan Zheng², Xilai Zheng³, Shiqiang Jiang⁴, Min Cao⁴, Marc Walther⁵, Chunhui Lu⁶

Affiliations

¹ College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; College of Marine Geosciences, Ocean University of China, Qingdao 266100, China.
² College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; Key Laboratory of Marine Environment and Ecological Education, Ocean University of China, Qingdao 266100, China. Electronic address: zhengtianyuan@ouc.edu.cn.
³ College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China; Key Laboratory of Marine Environment and Ecological Education, Ocean University of China, Qingdao 266100, China.
⁴ Qingdao Hydrological Center, Qingdao 266101, Shandong, China.
⁵ Helmholtz-Centre for Environmental Research-UFZ Leipzig, Department of Environmental Informatics, 04318 Leipzig, Germany.
⁶ State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, China.

PMID: 36931511
DOI: 10.1016/j.scitotenv.2023.162857

Abstract

For the coastal aquifers, recent research have shown that the tidal has a significant effect on saltwater intrusion in the near-shore aquifer. However, it is currently unclear how the tidal river contributes to the groundwater flow and salinity distribution in the upstream aquifer of the estuary. This study examined the effects of a tidal river on the dynamic characteristics of groundwater flow and salt transport in a tidal river-coastal aquifer system using field monitoring data and numerical simulations. It was found that changes in tidal-river level led to the reversal of groundwater flow. For a tidal cycle, the maximum area of seawater intrusion is about 41.16 km² at the end of the high tide stage. Then the area gradually decreased to 39.02 km² at the end of the low tide stage. More than 2 km² area variation can be observed in a tidal cycle. Compared to the low tide stage, the area of SWI increased by 5 % at high tide stage. The SWI region was also spreading landward from the tidal river. In addition, we quantified the water exchange and salt flux between the tidal river and aquifer. When the tidal fell below the level of the riverbed, the water exchange rate was stabilized at about -1.6 m/h. The negative value indicated that the river was recharged by the groundwater. With the increasing of tidal water level, the water exchange rate gradually changes from negative to positive and reached the maximum value of 3.2 m/h at the beginning of the falling tide stage. The presence of a physical river dam can amplify the difference in water level between high and low tides, thereby enhancing the influence of a tidal river on water exchange and salt flux. The findings lay the foundation for gaining a comprehensive understanding of the tidal river on groundwater flow and salt transport in upstream aquifers.

Keywords: Coastal aquifer; Numerical models; Saltwater intrusion; Tidal river; Water exchange.