Assessing the Effectiveness of Rainwater Infiltration Recharge in Mitigating Seawater Intrusion and Soil Salinization Based on Multiple Coupling Models: A Case Study in Zhuanghe, China

Abstract

Coastal regions often suffer from intertwined issues of seawater intrusion and soil salinization due to various factors. Although the application of rainwater infiltration measures in sponge city construction have shown effectiveness for stormwater control and water resource management, their potential and constraints in mitigating these coastal ecological issues remain unexplored. This study developed a coupled modeling approach integrating a rainwater infiltration model, variable density solute transport model, and statistical soil salinization model to assess the effectiveness of rainwater infiltration recharge in mitigating seawater intrusion and soil salinization in Zhuanghe, China. The models were calibrated and validated using monthly observational data and extensive field sampling measurements. Scenario simulation analyses for the next 20 years quantified sponge city implementation increased rainwater infiltration by 2.752 × 105 m3/a and raised groundwater levels by 4 m compared to non-sponge conditions, thereby mitigating seawater intrusion extent, with intrusion area and distance reduced by 21% and 33% respectively after 20 years. However, excessive infiltration rebounded soil salinity, reaching 0.015% higher than initial levels. A rainfall infiltration increase of approximately 2 × 105 m3/a was the optimal threshold for simultaneously mitigating regional seawater intrusion and soil salinization. This study introduces a systematic multi-model coupling approach to address interconnected coastal issues, delivering quantitative insights into designing sustainable infiltration recharge strategies through sponge city construction in coastal regions.

Keywords: Rainwater infiltration, Seawater intrusion, Soil salinization, Coupled modeling, Threshold analysis