Porosity vs. PermeabilityThe terms porosity and permeability are related.Porosity is a measure of the amount and size of porespace within an earth material, such as soil, clay, gravel,silt, rock, etc.Some rocks and soils are very porous, while others havevery little space between the particles.Porosity is how much water a material can hold. It isusually stated as a percentage of the material’s totalvolume.
Porosity vs. PermeabilityPermeability is a measure of the ability of an earthmaterial to let water pass through it.Permeability is affected by the size of the particles andshape of the spaces between the particles.Some materials have many spaces between particles,while others have virtually no space between particlesand are called impermeable.
Porosity vs. PermeabilityWater 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 passthrough it easily or quickly.If the spaces are large, such as in the gravel, the waterpasses through quickly.
Percolation and InfiltrationThere are two other terms that are used with water:percolation and infiltration.Infiltration is when the water enters the soil surfaceafter falling from the atmosphere.Percolation is the downward movement of water fromthe land surface into soil or porous rock, caused mainlyby gravity.
Groundwater vs. Surface WaterGroundwater is water that flows through the pores in therocks and soil beneath the surface of the ground.The groundwater trickles downward until it reaches animpermeable layer of soil or rock.We use wells and springs to pull groundwater back to thesurface to drink.Ninety-eight percent of Earth’s available freshwater isgroundwater.
Groundwater vs. Surface WaterSurface water includesrivers, streams, lakes, ponds, oceans, and even the waterthat runs down streets during thunderstorms.Surface water will, unless interfered with, flow downhilluntil it reaches a creek or stream. The creek or stream willeventually feed a river that will flow into the ocean. Alongthe way, some water will evaporate back into theatmosphere and will fall back to the Earth as rain.Surface water supplies 80% of the water used on a dailybasis.
Groundwater vs. Surface WaterSurface water which has not yetflowed into a creek is calledrunoff. Bare ground allows agreat deal of runoff to occur.Plants and dug ponds (asmall, shallow pond createdartificially by digging adepression in the land) reducethe amount of runoff.
Watershed vs. AquiferA watershed is an area of land where all of the surfacewater within a specified area drains downward andflows to the same place.Each drainage basin, or watershed, is separatedtopographically from adjacent basins.
AquiferAn aquifer is a natural, underground area where largequantities of ground water fill the spaces between rocksand sediment and accumulates.This water is available for use by using wells to pump outthe water.
Texas AquifersThe state of Texas has 23 aquifers that coverapproximately ¾ of the state.The Ogallala Aquifer accounts for about 90%of the water in all of Texas aquifers.Groundwater from Texas aquifers is usedfor irrigation, city use, manufacturing, andlivestock production.Pumping water from many aquifers in Texashas resulted in a significant lowering of thewater table. A map showing watersheds in Texas
More about AquifersLess permeable rock below an aquifer that keepsgroundwater from draining away is called a confining layeror aquitard.The water table in an aquifer is at the very top of the zoneof saturation.The zone of saturation is where water completely fills allthe interconnected pore spaces.
Water TableThe water table is the uppersurface of ground water below The water table fluctuateswhich the soil or rocks are both with the seasons andpermanently saturated with from year to year because it iswater and where the pressure of affected by climatic variationswater in the soil equals the and the amount ofpressure of the atmosphere. precipitation used by vegetation. It also is affected by withdrawing excessive amounts of water from wells.
PollutionPollution is the introduction of a contaminant into theenvironment.It is created mostly by human actions, but can also be aresult of natural disasters, such as flooding.Pollution has a harmful effect on any living organism inan environment, often making it impossible to sustainlife.Pollution to drinking water can cause diseases.