Porosity and Permeability in Earth Materials

Porosity vs. Permeability

• Porosity is the amount and size of pore space in earth materials (soil, clay, gravel, rock).
• Some materials are very porous (large spaces), while others have little space between particles.
• Porosity is the amount of water a material can hold, usually expressed as a percentage of the material's total volume.
• Permeability is the ability of an earth material to let water pass through it.
• Permeability depends on the size and shape of spaces between particles.
• Some materials have many spaces between particles, and are permeable. Others are impermeable (virtually no spaces).
• Water flows between spaces in the material.
• If spaces are small (clay), water clings and doesn't pass easily.
• If spaces are large (gravel), water passes quickly.

Percolation and Infiltration

• Percolation and infiltration are terms relating to water movement.
• Infiltration is when water enters the soil surface.
• Percolation is when water moves downwards through the soil or porous rock, mainly by gravity.

Groundwater vs. Surface Water

• Groundwater flows through pores in rocks and soil beneath the surface.
• It trickles downward until it reaches an impermeable layer.
• Wells and springs obtain groundwater.
• 98% of Earth's available freshwater is groundwater.
• Surface water includes rivers, streams, lakes, ponds, oceans, and water running during storms.
• Surface water flows downhill until reaching a creek or stream, eventually flowing into oceans.
• Some surface water evaporates and returns to Earth as rain.
• Surface water supplies 80% of daily water use.
• Runoff is surface water that doesn't flow into creeks or streams immediately (bare ground has lots of runoff).
• Plants and dug ponds reduce runoff.

Watersheds and Aquifers

• A watershed is an area of land where all surface water drains to the same place.
• Watersheds are topographically separated.
• An aquifer is a natural underground area with large quantities of groundwater.
• Groundwater fills the spaces between rocks and sediment.
• Texas has 23 aquifers.
• The Ogallala Aquifer provides 90% of Texas' aquifer water.
• Groundwater in Texas aquifers is used for irrigation, city use, manufacturing, and livestock.
• Pumping water from aquifers has lowered the water table significantly.

Water Table

• The water table is the upper surface of groundwater.
• Soil or rocks are permanently saturated below the water table.
• Water pressure at the water table equals atmospheric pressure.
• The water table fluctuates seasonally and annually due to precipitation and vegetation use.
• Excessive water withdrawal from wells affects the water table.

Pollution

• Pollution is the introduction of contaminants into the environment.
• Pollution is mostly caused by human actions, but can also result from natural disasters (e.g., flooding).
• Pollution harms all living organisms; it can make life unsustainable.
• Pollution of drinking water causes diseases.

Explore the concepts of porosity and permeability as they relate to various earth materials. This quiz covers the definitions, differences, and importance of these properties in water movement through soil and rocks. Test your understanding of infiltration and percolation processes!