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Groundwater -presents-. How large amounts of water are stored underground. How groundwater dissolves limestone and forms caves and other natural features.

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Presentation on theme: "Groundwater -presents-. How large amounts of water are stored underground. How groundwater dissolves limestone and forms caves and other natural features."— Presentation transcript:

1 Groundwater -presents-

2 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.

3 Infiltration Porosity Zone of saturation Water table Permeability Impermeable Aquifer Topography Cave Stalactite Stalagmite Travertine Spring Geyser Drawdown Artesian Well

4 The Hydrosphere The hydrosphere is water on or in Earth’s crust. “hydros” is the Greek word for water. 97% Ocean Water 3% freshwater

5 97% Ocean Water From the 3% of freshwater, how much do you think is trapped in the polar ice caps and glaciers? a. 10% b. 50% c. 90%

6 ?? ?? ?? ?? What is the greatest source of freshwater on Earth? a.Polar caps a.Glaciers a.Both a and b

7 Precipitation and Groundwater

8 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.

9 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.

10 Groundwater Storage The amount of space between rock particles in underlying sediment is referred to as porosity. Well sorted High sediments Porosity

11 Groundwater Storage The amount of space between rock particles in underlying sediment is referred to as porosity. Poorly sorted Low sediments Porosity

12 Groundwater Storage Q: Which of these two do you think will absorb groundwater faster after rainfall? a.b.

13 Groundwater Storage The porosity of sand can range from 2% to 50% ! The greater the porosity…the faster water is absorbed.

14 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.

15 The Zone of Saturation The upper boundary of the zone of saturation is called the water table.

16 The Zone of Saturation Only the water that exists in the Zone of saturation is called groundwater.

17 The Zone of Saturation Zone of aeration – materials are moist but contain mostly air.

18 The Water Table The depth of the water table varies with the slope of the land.

19 The Water Table The topography of the water table follows the contours of the land.

20 The Water Table The water table rises and falls depending on the season and the amount of precipitation.

21 ?? ?? ?? ?? Where is the water table closest to Earth’s surface? a.Floodplain a.A Swamp a.A Hilltop

22 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

23 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

24 Groundwater Movement Because water has to squeeze through the small pores in the subsurface material, it usually travels very slow. 1 mm

25 Groundwater Movement Sometimes the pores are so small not even a single water molecule can get through. 1 mm 0.1 mm vs.

26 Groundwater Movement The ability of a material to let water pass through it is called permeability. 1 mm 0.1 mm vs.

27 Groundwater Movement Q: Which of the two examples of sediment above have the highest permeability. 1 mm 0.1 mm vs. 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).

28 Groundwater Movement 0.1 mm With such tiny pores, some fine grained material is considered impermeable. 0.1 mm Flow velocities in impermeable materials are often measured in m/yr (meters per year). Examples of impermeable materials are silt, clay, and shale.

29 ?? ?? ?? ?? What two factors determine the flow velocity of groundwater? Answer: The flow velocity depends on the slope of the water table and the permeability of subsurface materials.

30 Groundwater Movement Most groundwater flow takes place through permeable layers called aquifers.

31 Groundwater Movement Impermeable layers called aquacludes are barriers to groundwater flow.

32 ?? ?? ?? ?? What is an aquifer? Answer: An aquifer is a permeable layer that allows groundwater to flow through it.

33 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).

34 Caves Caves form near or below the water table.

35 Caves Stream valleys are lowered and streams become empty as they infiltrate cave openings.

36 Caves Collapsing caves (or dissolved bedrock) near the surface of the Earth produce sink holes on the Earth’s surface.

37 ?? ?? ?? ?? Since the Limestone area of an aquifer is filled with “cavities”, how would this affect the rate of groundwater flow? 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.

38 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”.

39 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!

40 ?? ?? ?? ?? So what happens when an aquifer meets an aquaclude? Answer: The aquaclude stops water flow…so when aquifers and aqucludes meet, water is forced out of the Earth….see photo on page 249.

41 Springs When aquifers meet aquacludes at or near the surface of the Earth, water is forced out of the Earth….thus producing a SPRING.

42 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.

43 Springs In areas where there is horizontal sedimentary rock, Springs emerge in valleys very close to aquifers.

44 Springs Springs can occur at the edges of perched water tables.

45 Springs Sometimes Springs emerge along fault lines! Springs can also emerge at fault lines.

46 Springs Sometimes Springs emerge along fault lines! In Limestone regions, springs discharge water from underground pathways.

47 Winter Summer Temperature Of Springs Spring water can be hot, warm, or cold….depending upon where the spring is located. Air Water Air Water

48 Temperature Of Springs

49 Temperature Of Springs Hot Springs are defined as groundwater with temperatures higher than that of the human body.

50 ?? ?? ?? ?? So where do hot springs get their “heat” from ? Answer: Hot Springs get their “heat” from aquifers deep within the Earth.

51 Temperature Of Springs Sometimes the groundwater from these aquifers absorb so much heat…..they erupt! Hot Springs that erupt are called geysers!

52 Wells The red dashed line represents where the water table used to be before most of the water was pumped out!

53 Wells The distance between the deepest part of the cone of depression and the “old” Water table line is called drawdown.

54 Wells Eventually, water from runoff and precipitation is added back to the zone of saturation. This process is called recharge.

55 Confined Aquifers Water-table aquifers are often polluted when chemicals spill on surface sediment.

56 Confined Aquifers If an aquifer is located between two aquacludes, it can be protected from pollution.

57 Confined Aquifers In essence, the aquacludes become “body guards” to the aquifer.

58 Confined Aquifers An aquifer “sandwiched” between two aquacludes is referred to as a Confined Aquifer.

59 Confined Aquifers Confined aquifers usually contain water under pressure since the area of “recharge” is at a higher elevation.

60 Confined Aquifers Confined aquifers usually contain water under pressure since the area of “recharge” is at a higher elevation.

61 Confined Aquifers This type of aquifer is called an Artesian aquifer and water that spurts from it is called an Artesian Well.

62

63 Pollutants from sewage travel downslope to contaminate wells.

64 Protecting Our Water Supply There are a number of ways in which groundwater resources can be protected and restored. All major pollution sources need to be identified and eliminated.


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