Water Resources and Pollution in Environmental Science Practice Test

Water movement after rainfall splits between infiltrating the soil to become groundwater recharge and flowing over the surface as runoff. Porosity is the amount of void space in soil that can store water, so higher porosity means more water can be stored in the soil and available to recharge groundwater. Infiltration is the process of water entering the soil; when infiltration is efficient, a larger fraction of rainfall becomes soil water rather than surface runoff, which helps prevent erosion by reducing the velocity and amount of water flowing over the surface. Put together, higher infiltration capacity and higher porosity lead to more groundwater recharge and less surface runoff and erosion.

Porosity clearly affects groundwater recharge because it provides the storage that can hold infiltrated water. It’s not correct to say infiltration decreases with increased porosity, and infiltration is not inherently tied to faster flow causing more runoff; runoff is more about rainfall exceeding the soil’s infiltration capacity than about quickening flow through pores.