What do we call the layer of rock that restricts water movement in confined aquifers?

In the context of hydrogeology, the layer of rock that restricts water movement in confined aquifers is called an aquitard. An aquitard is typically composed of materials such as clay or silt, which have low permeability and prevent water from moving freely through it. This characteristic is essential in differentiating confined aquifers from unconfined aquifers. In confined aquifers, the water is trapped between impermeable layers (aquitards), leading to increased pressure in the water-bearing layers.

The other terms listed, while related to water movement and aquifers, do not describe the layer that restricts water movement. Pore space refers to the voids within sediments or rocks that can hold water, but it does not define a layer that impedes flow. The capillary zone refers to the area above the water table where water is held by surface tension, and it does not function as a barrier. Lastly, the water table marks the upper boundary of an unconfined aquifer, representing the level below which the ground is saturated with water; it also does not act as a confining layer. Thus, the correct identification of an aquitard accurately describes its critical role in the structure and function of confined aquifers.