What is the term for the boundary between the saturated and unsaturated zones in soil or rock?

The boundary between the saturated and unsaturated zones in soil or rock is known as the water table. This is the level at which the soil or rock is fully saturated with water, below which all the pore spaces are filled with water. Above the water table lies the unsaturated zone, where the pores contain both air and water.

The water table can fluctuate based on several factors, including rainfall, evaporation, and water extraction for human use. Understanding the water table is essential in hydrology, environmental science, and water resource management, as it influences groundwater availability and soil moisture levels. The capillary fringe, while related to the water table, refers specifically to the area just above the water table where water is held in soil pores due to surface tension. Groundwater surface typically refers to the same concept as the water table but is less commonly used. A soil horizon pertains to distinct layers within soil profiles and does not define the boundary between saturated and unsaturated zones.