Effect of Groundwater Depression Cone on the Hydrochemical Evolution Process in the People’s Victory Canal Irrigation Area, China

The over-exploitation of shallow groundwater in the People’s Victory Canal irrigation area has led to the continuous decline in the groundwater level. The formation of a groundwater drawdown cone has changed the original runoff conditions and hydrochemical environment. Based on the groundwater data in the irrigated area from 1996 to 2022, multivariate statistical analysis, traditional hydrochemical methods, and inverse geochemical modeling were used to reveal the impact of the formation of the groundwater depression cone on hydrochemical evolution. The results show that the formation of the groundwater depression cone near the central area in 2003 changed the direction of the canal head flowing to the northwest area, making the groundwater flow from the canal head and the northwest area to the central area. The change in the hydrodynamic fields also caused the groundwater with high salinity in the northwest region to flow to the funnel area, and the ion concentration of groundwater along the pathway area to increase. The groundwater type in the runoff area changes, gradually evolving from Group 1 to Group 2 groundwater. Analysis of the hydrochemical characteristics of groundwater in the runoff area for many years shows that after the formation of the central funnel area in 2003, the groundwater with high ${\mathrm{SO}}_4^{2-}$ ion in the northwest area flows to the funnel area, and the correlation between total dissolved solids and $\mathrm{S}{\mathrm{O}}_4^{2-}$ ions in the groundwater along the way is significantly enhanced. The inverse geochemical modeling shows that the main water–rock action along the runoff direction is the dissolution of halite and gypsum. In addition, the study area has a strong cation exchange reaction.