2Porosity vs. Permeability The terms porosity and permeability are related.Porosity is a measure of the amount and size of pore space within an earth material, such as soil, clay, gravel, silt, rock, etc.Some rocks and soils are very porous, while others have very little space between the particles.Porosity is how much water a material can hold. It is usually stated as a percentage of the material’s total volume.
3Porosity vs. Permeability Permeability is a measure of the ability of an earth material to let water pass through it.Permeability is affected by the size of the particles and shape of the spaces between the particles.Some materials have many spaces between particles, while others have virtually no space between particles and are called impermeable.
4Porosity vs. Permeability Water flows between the spaces in the material.If the spaces are close together, such as in clay based soils, the water will tend to cling to the material and not pass through it easily or quickly.If the spaces are large, such as in the gravel, the water passes through quickly.
5Percolation and Infiltration There are two other terms that are used with water: percolation and infiltration.Infiltration is when the water enters the soil surface after falling from the atmosphere.Percolation is the downward movement of water from the land surface into soil or porous rock, caused mainly by gravity.
7Groundwater vs. Surface Water Groundwater is water that flows through the pores in the rocks and soil beneath the surface of the ground.The groundwater trickles downward until it reaches an impermeable layer of soil or rock. We use wells and springs to pull groundwater back to the surface to drink.Ninety-eight percent of Earth’s available freshwater is groundwater.
8Groundwater vs. Surface Water Surface water includes rivers, streams, lakes, ponds, oceans, and even the water that runs down streets during thunderstorms.Surface water will, unless interfered with, flow downhill until it reaches a creek or stream. The creek or stream will eventually feed a river that will flow into the ocean. Along the way, some water will evaporate back into the atmosphere and will fall back to the Earth as rain. Surface water supplies 80% of the water used on a daily basis.
9Groundwater vs. Surface Water Surface water which has not yet flowed into a creek is called runoff. Bare ground allows a great deal of runoff to occur. Plants and dug ponds (a small, shallow pond created artificially by digging a depression in the land) reduce the amount of runoff.
11Watershed vs. AquiferA watershed is an area of land where all of the surface water within a specified area drains downward and flows to the same place.Each drainage basin, or watershed, is separated topographically from adjacent basins.
12AquiferAn aquifer is a natural, underground area where large quantities of ground water fill the spaces between rocks and sediment and accumulates.This water is available for use by using wells to pump out the water.
13A map showing watersheds in Texas Texas AquifersThe state of Texas has 23 aquifers that cover approximately ¾ of the state.The Ogallala Aquifer accounts for about 90% of the water in all of Texas aquifers.Groundwater from Texas aquifers is used for irrigation, city use, manufacturing, and livestock production.Pumping water from many aquifers in Texas has resulted in a significant lowering of the water table.A map showing watersheds in Texas
14More about AquifersLess permeable rock below an aquifer that keeps groundwater from draining away is called a confining layer or aquitard.The water table in an aquifer is at the very top of the zone of saturation.The zone of saturation is where water completely fills all the interconnected pore spaces.
15Water TableThe water table is the upper surface of ground water below which the soil or rocks are permanently saturated with water and where the pressure of water in the soil equals the pressure of the atmosphere.The water table fluctuates both with the seasons and from year to year because it is affected by climatic variations and the amount of precipitation used by vegetation. It also is affected by withdrawing excessive amounts of water from wells.
16PollutionPollution is the introduction of a contaminant into the environment.It is created mostly by human actions, but can also be a result of natural disasters, such as flooding.Pollution has a harmful effect on any living organism in an environment, often making it impossible to sustain life.Pollution to drinking water can cause diseases.