EarthScience -presents- Groundwater
What You’ll Learn • How large amounts of water are stored underground. • How groundwater dissolves limestone and forms caves and other natural features. • How groundwater is removed from the ground by humans and what problems endanger our groundwater supply.
Vocabulary Terms • Infiltration • Porosity • Zone of saturation • Water table • Permeability • Impermeable • Aquifer • Topography • Cave • Stalactite • Stalagmite • Travertine • Spring • Geyser • Drawdown • Artesian Well
Movement and storage of groundwater 3% freshwater The Hydrosphere • The hydrosphere is • water on or in • Earth’s crust. • “hydros” is the Greek word for water. 97% Ocean Water
Movement and storage of groundwater 10% 50% 90% From the 3% of freshwater, how much do you think is trapped in the polar ice caps and glaciers? 97% Ocean Water
? ? ? ? Polar caps Glaciers Both a and b What is the greatest source of freshwater on Earth?
Movement and storage of groundwater Precipitation and Groundwater
Movement and storage of groundwater Precipitation and Groundwater • Much of the precipitation • that falls on land enters the ground through a process called infiltration and becomes groundwater. • Only a small portion of runoff is directly returned to the oceans through streams and rivers. Precipitation
Movement and storage of groundwater Precipitation and Groundwater • Solid precipitation such as snow takes a long while before it becomes runoff or infiltrates to become groundwater. • Eventually, the groundwater returns to the surface through springs and then flows back to the ocean. Precipitation
Movement and storage of groundwater Groundwater Storage The amount of space between rock particles in underlying sediment is referred to as porosity. Well sorted High sediments Porosity
Movement and storage of groundwater Groundwater Storage The amount of space between rock particles in underlying sediment is referred to as porosity. Poorly sorted Low sediments Porosity
Movement and storage of groundwater Groundwater Storage a. b. Q: Which of these two do you think will absorb groundwater faster after rainfall?
Movement and storage of groundwater Groundwater Storage The porosity of sand can range from 2% to 50% ! The greater the porosity…the faster water is absorbed.
Movement and storage of groundwater The Zone of Saturation The depth below the Earth’s surface at which groundwater completely fills the pores of material is called the zone of saturation.
Movement and storage of groundwater The Zone of Saturation The upper boundary of the zone of saturation is called the water table.
Movement and storage of groundwater The Zone of Saturation Only the water that exists in the Zone of saturation is called groundwater.
Movement and storage of groundwater The Zone of Saturation Zone of aeration– materials are moist but contain mostly air.
Movement and storage of groundwater The Water Table The depth of the water table varies with the slope of the land.
Movement and storage of groundwater The Water Table The topography of the water table follows the contours of the land.
Movement and storage of groundwater The Water Table The water table rises and falls depending on the season and the amount of precipitation.
? ? ? ? Floodplain A Swamp A Hilltop Where is the water table closest to Earth’s surface?
Movement and storage of groundwater Groundwater Movement In saturated sediment all materials are coated with a thin film of motionless water. In coarse grained materials like sand, this film occupies a relatively small portion of the “pore space”. 1 mm
Movement and storage of groundwater Groundwater Movement Because of this moving water can flow freely past the open pore spaces. Groundwater flows downhill due to gravity and in the direction of the landscape slope. 1 mm
Movement and storage of groundwater Groundwater Movement Because water has to squeeze through the small pores in the subsurface material, it usually travels very slow. 1 mm
Movement and storage of groundwater Groundwater Movement vs. 0.1 mm 1 mm Sometimes the pores are so small not even a single water molecule can get through.
Movement and storage of groundwater Groundwater Movement vs. 0.1 mm 1 mm The ability of a material to let water pass through it is called permeability.
Movement and storage of groundwater Groundwater Movement vs. 0.1 mm 1 mm Q: Which of the two examples of sediment above have the highest permeability. Highly permeable materials include sandstone, limestone, and fractured bedrock. Flow rates for these materials can be as fast as 1 m/h (one meter per hour).
Movement and storage of groundwater Groundwater Movement 0.1 mm 0.1 mm With such tiny pores, some fine grained material is considered impermeable. Examples of impermeable materials are silt, clay, and shale. Flow velocities in impermeable materials are often measured in m/yr (meters per year).
? ? ? ? Answer: The flow velocity depends on the slope of the water table and the permeability of subsurface materials. What two factors determine the flow velocity of groundwater?
Movement and storage of groundwater Groundwater Movement Most groundwater flow takes place through permeable layers called aquifers.
Movement and storage of groundwater Groundwater Movement Impermeable layers called aquacludesare barriers to groundwater flow.
? ? ? ? What is an aquifer? Answer: An aquifer is a permeable layer that allows groundwater to flow through it.
Groundwater Systems Springs Aquifers are commonly composed of sand, gravel, sandstone and limestone. Remember: Limestone is easily dissolved by groundwater…..that’s how cavities in aquifers appear. (A cavity is an open space…like a cave).
Groundwater Erosion and Deposition Caves Caves form near or below the water table.
Groundwater Erosion and Deposition Caves Stream valleys are lowered and streams become empty as they infiltrate cave openings.
Groundwater Erosion and Deposition Caves Collapsing caves (or dissolved bedrock) near the surface of the Earth produce sink holeson the Earth’s surface.
? ? ? ? Answer: Since there are a lot of open spaces due to dissolved limestone, the ground water can flow FASTER in this area of an aquifer. Since the Limestone area of an aquifer is filled with “cavities”, how would this affect the rate of groundwater flow?
Groundwater Erosion and Deposition Caves Caves are usually located just beneath the water table. As water drips from the ceiling of a cave, it leaves behind small trace amounts of minerals found within the water itself. After a long period of time, these minerals collect to form cone shaped structures called “stalactites”.
Groundwater Erosion and Deposition Caves As the water drips to the floor, minerals left begin to build up mound shaped, dripstone deposits. This type of deposit is called a “stalagmite”. Eventually, stalactites and stalagmites will join together to form dripstone columns within the cave!
? ? ? ? Answer: The aquaclude stops water flow…so when aquifers and aqucludes meet, water is forced out of the Earth….see photo on page 249. So what happens when an aquifer meets an aquaclude?
Groundwater Systems Springs When aquifers meet aquacludesat or near the surface of the Earth, water is forced out of the Earth….thus producing a SPRING.
Groundwater Systems Springs The volume of water produced by a spring can be a mere trickle or a raging river! In a “Karst Region”, springs yield extremely fast moving waters….. they’re called Super Springs.
Groundwater Systems Springs In areas where there is horizontal sedimentary rock, Springs emerge in valleys very close to aquifers.
Groundwater Systems Springs Springs can occur at the edges of perched water tables.
Groundwater Systems Springs Sometimes Springs emerge along fault lines! Springs can also emerge at fault lines.
Groundwater Systems Springs Sometimes Springs emerge along fault lines! In Limestone regions, springs discharge water from underground pathways.
Temperature Of Springs Groundwater Systems Spring water can be hot, warm, or cold….depending upon where the spring is located. Groundwater vs. Air Water Air Temperature Air Water Winter Summer
Temperature Of Springs Groundwater Systems
Temperature Of Springs Groundwater Systems Hot Springs are defined as groundwater with temperatures higher than that of the human body.
? ? ? ? Answer: Hot Springs get their “heat” from aquifers deep within the Earth. So where do hot springs get their “heat” from?