Water Table and Aquifers

What is Ground Water?

• Ground Water: Water beneath the surface trapped in sediment and rock is called groundwater

• MOST OF THE FRESH water available for human use is groundwater.

What happens to all of the water that falls from the sky?

• Evaporated into gas again

• Surface run-off to large bodies of water

• Taken up by organisms

• Percolates into soil

What allows the water to percolate into the ground?

• Porosity and permeability-

• These are determined by the materials or types of rocks in the ground

• Water table-the upper level of the ground that is saturated with water.

• The water is still moving, very slowly, and it is still part of the water cycle.

• Most of the water in the ground comes from precipitation that infiltrates downward from the land surface.

Why is the water table important?

• It is important because we can drill down to the level of saturation and bring up the groundwater as long as the material is permeable enough to pump water through.

Is the water table always in the same place?

• It is not level-it increases and decreases with the peaks and valleys of the land’s surface

Ground Water

Unsaturated zone• Zone that has some

soil water, but varies due to rainfall

• This area of the soil is not saturated with water

Saturated zone • Porous or

permeable zone of soil that is saturated with water

Aquifers

• Another term for ground water is "aquifer,"

• This term is usually used to describe rock or soil formations capable of yielding enough water to supply peoples' uses.

• Aquifers are a huge storehouse of Earth's freshwater

How do we extract ground water from an aquifer?

• We can extract ground water using a pump

• We can only extract water from the ground if the aquifer is shallow enough (not too deep)

• AND if the water is flowing through the material the aquifer is made of (sandstone etc.)

Different Kinds of Aquifers

Unconfined• When the “confining”

layer of impermeable material is under the aquifer

• This Aquifer is unconfined.

• When the Aquifer is under the impermeable confining layer

• This Aquifer is confined by a layer of impermeable material above it.

• This Aquifer is considered to be artesian.

Confined

Different Kinds of Aquifers

What is an “artesian” well?

• A well that is dug into an artesian aquifer. • An artesian aquifer is an aquifer that is

sandwiched between 2 layers of impermeable material

• This causes pressure to force the water up and to flow out of the well without pumping.

• Do all wells need pumps?• No pump is needed if the well is in a confined aquifer

and the surface of the well is below the water table

• Is there a danger associated with pumping all of the ground water out of a location?

• Yes-recharge rate (rates of water entering the aquifer) occur very slowly

Recharge Zones

• Groundwater flows paths from areas of recharge to areas of discharge.

• Recharge occurs everywhere precipitation that falls on the land surface soaks into the ground, moves through the unsaturated zone, and enters the saturated parts of the subsurface.

• Recharge also can come from water in surface water bodies moving into the ground.

Discharge Zones

• Discharge from the saturated subsurface material occurs at springs, streams, lakes, wetlands, bays, the ocean in coastal areas, and as transpiration by plants whose roots extend to near the water table.