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