perched water table

When a lens of groundwater hovers in isolation above the general water table and is entirely separate from it, it’s viewed as being perched there. The lens is created when surface water, percolating through the ground, encounters an isolated layer of bedrock or impermeable soil, a mass of limited extent. Perched water tables most often occur in areas with level topography, high rainfall, and poor drainage. Well diggers eagerly seek them out because they’re closer to the surface than the main water table. Occasionally, a perched water table forms at such a shallow depth it intersects the ground surface and produces a flowing spring.

Terry Tempest Williams