What is the process called when soil water trickles downward through soil until it reaches an impervious layer?

The process whereby soil water trickles downward through soil until it reaches an impervious layer is called percolation. This term specifically refers to the movement of water through the soil and porous rocks, where the water migrates under the influence of gravity. As water percolates, it is filtered and can become part of the groundwater supply if it passes through various soil layers. The presence of an impervious layer, like bedrock or clay, signifies the end of this downward movement, as the water cannot pass through this layer.

In contrast, infiltration refers to the initial process of water entering the soil surface. Evapotranspiration involves the combined processes of evaporation and plant transpiration that contribute to the loss of water from the soil, rather than its downward movement. Absorption typically describes how plant roots take up water from the soil, rather than the movement of water through the soil profile. Each of these other terms highlights different aspects of the water cycle, but percolation is the most accurate term for the process described in the question.