Water Beneath the SurfaceWater Beneath the Surface

6.36.3

There is Water Underground

There is Water Underground

Pore spaces + fractures and joints = lots of openings Water collects underground

Pore spaces + fractures and joints = lots of openings Water collects underground

What happens when it rains?

What happens when it rains?

Runs off, evaporates, soaks into ground

Underground water depends on: Steepness of slopes Surface materials Intensity and duration of rain Vegetation type Amount of vegetation

Runs off, evaporates, soaks into ground

Underground water depends on: Steepness of slopes Surface materials Intensity and duration of rain Vegetation type Amount of vegetation

Where does the water in the soil go?

Where does the water in the soil go?

Seeps downward until the zone of saturation Zone of saturation

= area where water fills all of the open spaces in sediment and rock

Groundwater is in zone of saturation

Seeps downward until the zone of saturation Zone of saturation

= area where water fills all of the open spaces in sediment and rock

Groundwater is in zone of saturation

Water TableWater Table

Upper limit of zone of saturation

Water can be pumped

Above the water table = not saturated = zone of aeration

Wells can’t pump water from zone of aeration

Upper limit of zone of saturation

Water can be pumped

Above the water table = not saturated = zone of aeration

Wells can’t pump water from zone of aeration

Porosity and PermeabilityPorosity and Permeability

Flow and storage of groundwater depend on material underground

Porosity = percentage of pore spaces (spaces between sedimentary particles)

Permeability = ability to flow Rock can be porous and not very

permeable

Flow and storage of groundwater depend on material underground

Porosity = percentage of pore spaces (spaces between sedimentary particles)

Permeability = ability to flow Rock can be porous and not very

permeable

How does groundwater move?

How does groundwater move?

Twisting and turning through small openings

Moves more slowly when pore spaces are smaller Too small --> water can’t move Ex: clay = high porosity but impermeable

Aquifers = transmit groundwater freely Source of well water

Twisting and turning through small openings

Moves more slowly when pore spaces are smaller Too small --> water can’t move Ex: clay = high porosity but impermeable

Aquifers = transmit groundwater freely Source of well water

AquiferAquifer

SpringsSprings

Spring = flow of groundwater naturally at the surface water table intersects

the ground surface

Hot spring = 6-9 °C hotter than the average annual air temperature

Spring = flow of groundwater naturally at the surface water table intersects

the ground surface

Hot spring = 6-9 °C hotter than the average annual air temperature

GeysersGeysers

Hot spring where column of water shoots up at intervals

Ex: Old Faithful Superheated water

expands some water forced out

at the surface Loss of water =

decreases pressure Some water turns to

steam Geyser erupts

Hot spring where column of water shoots up at intervals

Ex: Old Faithful Superheated water

expands some water forced out

at the surface Loss of water =

decreases pressure Some water turns to

steam Geyser erupts

WellsWells

Hole bored into the zone of saturation Biggest user:

irrigation for agriculture

Must go far below the water table

Cone of depression = withdraw more water than is replenished

Hole bored into the zone of saturation Biggest user:

irrigation for agriculture

Must go far below the water table

Cone of depression = withdraw more water than is replenished

Artesian WellArtesian Well

Most wells need to be pumped in order to get water

Artesian well = groundwater rises on its own under pressure Water in aquifer

that is tilted Water can’t escape

Most wells need to be pumped in order to get water

Artesian well = groundwater rises on its own under pressure Water in aquifer

that is tilted Water can’t escape

CavernsCaverns Limestone = easily

weathered by groundwater groundwater contains

carbonic acid Carbonic acid weathers

rock Cavern = naturally formed

underground chamber Erosion forms most

caverns at or below the water table in the zone of saturation Dissolving process slowly

creates cavities and caverns

Limestone = easily weathered by groundwater groundwater contains

carbonic acid Carbonic acid weathers

rock Cavern = naturally formed

underground chamber Erosion forms most

caverns at or below the water table in the zone of saturation Dissolving process slowly

creates cavities and caverns

CavernsCaverns

Stalactites = hang from the ceiling of a cavern Water seeps through

cracks in the cavern’s ceiling

Stalagmites = develop on the floor of the cavern Water falls from the

ceiling and splatters on the floor

Stalactites = hang from the ceiling of a cavern Water seeps through

cracks in the cavern’s ceiling

Stalagmites = develop on the floor of the cavern Water falls from the

ceiling and splatters on the floor

Karst TopographyKarst Topography

Underlain by limestone

Evidence of groundwater erosion seen at the surface US = limestone Kentucky, Florida,

Tennessee, soutern Indiana, Alabama

Lack of streams

Underlain by limestone

Evidence of groundwater erosion seen at the surface US = limestone Kentucky, Florida,

Tennessee, soutern Indiana, Alabama

Lack of streams

SinkholesSinkholes

Karst areas have sinkholes = depression because groundwater has removed soluble rock Some happen

gradually, some happen suddenly

Karst areas have sinkholes = depression because groundwater has removed soluble rock Some happen

gradually, some happen suddenly

Environmental ProblemsEnvironmental Problems

Land Subsidence = large amounts of groundwater have been withdrawn Groundwater

supplies are finite Water pumped

from wells faster than it can be replaced Ground sinks Ex: California

Land Subsidence = large amounts of groundwater have been withdrawn Groundwater

supplies are finite Water pumped

from wells faster than it can be replaced Ground sinks Ex: California

Groundwater ContaminationGroundwater

Contamination Sewage from septic tanks, farm

wastes, broken sewers Highly permeable means increase

in groundwater contamination Fertilizers spread across land,

pesticides, highway salt

Sewage from septic tanks, farm wastes, broken sewers

Highly permeable means increase in groundwater contamination

Fertilizers spread across land, pesticides, highway salt

What happens if groundwater is polluted?

What happens if groundwater is polluted?

Abandon the water supply = pollutants flush out gradually Aquifer unused for years

Pump out and treat polluted water Aquifer recharges naturally

Prevention

Abandon the water supply = pollutants flush out gradually Aquifer unused for years

Pump out and treat polluted water Aquifer recharges naturally

Prevention