Where is the water on Earth?Look at the next slide’s diagram. In ityou’ll see that most of the water on Earthis salt water. Out of the fresh water, mostis frozen. Groundwater makes up thelargest portion of fresh, liquid water onEarth.
Where is groundwater and how does it get there?The Water Cycle shows us how watermoves from phase to phase (gas, liquidand solid) and from place to place onEarth.Water that infiltrates into the earthbecomes groundwater.
Where do you find groundwater?Groundwater can be found in betweenindividual pieces of sediment in a layer ofunconsolidated material (not solid rock,but layers of sand, gravel, silt, etc.)Groundwater can also be found in thespaces that exist within solid rock.– Either pore spaces between individual grains– Or in cracks that exist in solid rock
Intergranular = pore spaces in solid rockor unconsolidated materialFractured bedrock = cracks in solid rockSolution enhanced = cracks that havebeen enlarged by groundwater dissolvingrock
Types of AquifersAn aquifer is a layer of sediment or rockcapable of holding and transmittingsignificant quantities of water.Aquifers that have an impermeable layerabove and below them are called“confined aquifers”What’s an impermeable layer? A layer ofrock or sediment that doesn’t allow waterto flow through easily.
Unconfined aquiferAlso called a “Water Table” aquifer, thistype does not have an impermeable layerabove the aquifer.See the next slide for a diagram showingtwo confined aquifers and one unconfinedaquifer.
The Confining beds are also calledaquitards. They retard, or slow, the flow of water.
Other termsThe water table is the top of the saturatedzone.The saturated zone is the layer in theaquifer where every pore space or everycrack is completely filled with waterThe unsaturated zone exists above thesaturated zone, and may have moisture,but the pore spaces or cracks also containair.
Vadose zone and zone of aeration areother words for the unsaturated zone.Water from the saturated zone can moveupward through capillary action into theunsaturated zone.
Water table divides the two zones. Theposition of the water table will vary. More recharge raises the water table.
Source of water – UnconfinedIn an unconfined aquifer, water will seep intothe ground directly above the aquifer. This isthe recharge area.
Source of water - ConfinedIn a confined aquifer, the overlying aquitardprevents water from the surface fromseeping into the aquifer.Recharge, therefore, often comes from faraway, in a place where the aquifer meets upwith the surface.See the illustration on the next page.
Streams as a source of groundwater recharge (mostly in dry climates) In locations where the water table is below the bottom of the stream, water from the stream can run into the ground and feed the groundwater. This is called a losing stream or an influent stream.
Induced recharge into wells from streamsThere are some situations where, even in humid climates, water from streams ends up in wells. This occurs when a pumping well is located in an aquifer near a river. Water from the river is pulled into the pumping well. These tend to be very productive wells – there’s a constant source of water. However, it is river water, albeit, filtered through the ground, but there can be quality issues.
Streams feeding groundwater through “Induced Recharge”