Exploring the effects of reducing groundwater pumping on downward saltwater intrusion into deep aquifers in coastal Tianjin, China

Abstract

In this study, a 3D variable-density groundwater flow and salt transport model was developed and calibrated to simulate spatial and temporal variation of groundwater salinity in Binhai New Area located at coastal Tianjin Municipality for tracking saltwater/freshwater interface depth, analyzing saltwater descending velocity, and determining downward saltwater intrusion ceasing time under the background of rigorous groundwater pumping regulations (groundwater pumping rate reducing to zero in 2023). Results indicated that: (1) saltwater/freshwater interface depths in the northern area would increase from 130–170 m to 150–190 m from 2016 to 2031, in the central area would increase from 180–230 m to 210–260 m from 2016 to 2030, and in the southern area would increase from 280–300 m to 300–320 m from 2016 to 2030 and then stay unchanged, respectively; (2) saltwater descending velocities in the northern, central, and southern area decrease linearly and will reach zero in the years of 2031, 2030, and 2030, respectively; and (3) enlargement of the extent of downward saltwater intrusion will cease since 2031 in the northern area or 2030 in the central and southern area. To the best knowledge of the authors, this research is the first effort to unravel the fact of vertical saltwater intrusion (saltwater descending) occurred in coastal Tianjin, which demonstrates an urgent need for rigorous pumping regulations of reducing groundwater exploitation.