In the context of global warming, rising sea levels are intensifying seawater intrusion in coastal areas. Due to the complex hydrodynamic conditions and increasing groundwater over-extraction in these regions, understanding the patterns of seawater intrusion is crucial for effective prevention and control. This study employed a sandbox model to investigate both vertical and horizontal seawater intrusion into a coastal unconfined aquifer with an impermeable dam under varying conditions of sea level rise, coastal slope, and groundwater pumping rate. Additionally, a two-dimensional SEAWAT model was developed to simulate seawater intrusion under these experimental conditions. The results indicate that sea level rise significantly increases the extent and intensity of seawater intrusion. When sea level rises by 3.5 cm, 4.5 cm, and 5.5 cm, the areas of the saline wedge reached 362 cm2, 852 cm2, and 1240 cm2, respectively, with both horizontal and vertical intrusion ranges expanding considerably. When groundwater extraction is superimposed, vertical seawater intrusion is notably intensified. At an extraction rate of 225 cm3/min, the vertical intrusion areas corresponding to sea level rises of 3.5 cm, 4.5 cm, and 5.5 cm were 495 cm2, 1035 cm2, and 1748 cm2, respectively, showing significant expansion, and this expansion becomes more pronounced as sea levels rise. In contrast, slope variations had a significant impact only on vertical seawater intrusion. As the slope decreased from tanα = 1/5 to tanα = 1/9, the upper saline wedge area expanded from 525 cm2 to 846 cm2, considerably increasing the vertical intrusion range. Finally, the combined effects of groundwater extraction and sea level rise exacerbate seawater intrusion more severely than either factor alone, presenting greater challenges for coastal water resource management.
