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Groundwater

Chapter 14. Groundwater. Objectives. Explain how porosity and permeability affect the storage and movement of groundwater Describe the water table and features associated with it Explain how artesian formations affect groundwater Distinguish among hot springs, geysers, and fumaroles.

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Groundwater

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  1. Chapter 14 Groundwater

  2. Objectives • Explain how porosity and permeability affect the storage and movement of groundwater • Describe the water table and features associated with it • Explain how artesian formations affect groundwater • Distinguish among hot springs, geysers, and fumaroles

  3. 14.1 Water in the Ground

  4. Groundwater • When it rains some of that water seeps into the ground and is stored there. • Several factors affect how much water seeps into the ground • Type of rock or soil • Climate • Topography • Vegetation • Land use

  5. Porosity • The amount of water that soil or rock can hold depends upon the amount of space, or pore space, between the grains of the material • Porosity: the percent of a materials volume that is pore space

  6. Porosity • Particle shape • Rounded particles have a lot of pore space • Flat or angular particles have less pore space

  7. Porosity • Sorting • Pore space is greatest in materials made up of particles that are all the same size • Mixed materials have less pore space because smaller particles fill the space between larger particles

  8. Permeability • The rate at which water or other liquids pass through the pore spaces of a rock • Water passes easily through materials with large pore spaces • Impermeable: a material that water cannot pass through. • ex. fine grained clays and shale

  9. A material can be highly porous but not at all permeable • Ex: Pumice has many pores, but the pores are not connected so water cannot pass through • Nonporous rocks like granite can become permeable if cracks develop in the rock which allow water to pass through

  10. Zone of Saturation • When rain falls, it seeps into the ground until it reaches an impermeable material • Water will begin to fill in the pore spaces above the impermeable material • As more rain falls the water level rises higher and higher forming a “zone of saturation”

  11. The Water Table • The upper zone of saturation is called the water table

  12. Zone of Aeration • Located between the water table and the surface • A section that has air within the pore spaces

  13. Capillary Action

  14. Capillary Fringe • Where the zone of saturation and the zone of aeration meet • Water rises slightly because the water molecules are attracted to the soil particles (capillary action)

  15. The Water Table • The water tables distance from the surface can change depending on: • Amount of rainfall/Climate • Time between rains • Slope of the ground • Thickness of soil

  16. The Water Table • Climate • Humid climates: water table is near the surface in places such as swamps, lakes and rivers • Desert regions: water table may be hundreds of meters below ground

  17. Wells and Springs Aquifer: • Permeable layers of rock and sediment that store and carry ground water in enough quantity to supply wells Ordinary well: • When humans dig down to the surface of the water table • Must be deep enough to provide water even during dry seasons when the water table may drop

  18. Wells and Springs • Springs are formed where the water table meets the surface • Can be the result of a perched aquifer in which water accumulates on top of an impermeable layer that lies above the water table

  19. Artesian Formations • When an aquifer dips underground and is sandwiched between two layers of impermeable rocks • Gravity moves the water downward and creates pressure • When a well is drilled the pressure causes the water to rise up

  20. Hot Springs • When water comes up quickly through cracks from great depths below the surface • Groundwater may also become hot due to volcanic activity

  21. Geysers A hot spring that intermittently shoots columns of hot water and steam into the air • Formed from a tube that may extend hundreds of meters below the surface • The water becomes so hot that it expands and releases pressure through steam, pushing water out of the top

  22. 14.2 Conserving Groundwater

  23. Objectives • List the factors that affect a water budget • Describe the results of overuse of groundwater • Explain how groundwater becomes polluted

  24. Conserving Groundwater • 50% of drinking water in the United States comes from groundwater • Therefore, we must conserve and protect groundwater supplies

  25. Water Budgets Describe the income and spending of water for a region. • Income = rain or snow • Spending = water lost by runoff and evapotranspiration

  26. Water Budget Recharge: • When extra moisture that is not needed by plants soak into soil. • Leads to a moisture surplus

  27. Water Budget Surplus: • Occurs when rainfall is greater than the need for moisture and the soil water storage is filled • Water tables rises or water becomes part of stream runoff

  28. Water Budget Usage: • If the need for moisture > the rainfall, the plants can draw water from the soil water supply • If the need for moisture continues to be greater than the rainfall, all of the water available in the soil may be used up

  29. Water Budget Deficit: • Occurs when the need for moisture is greater than the rainfall and the soil water storage is gone.

  30. Groundwater Conservation • In many regions groundwater is being used faster than it can be replenished • Pollution threatens groundwater supplies

  31. Groundwater Pollution • Oil washed from roads • Nitrates from soil fertilizers • Pesticides • Farm Wastes • Sewage from septic tanks • Controversial drilling techniques such as fracking and other oil and gas extraction techniques • Fracking • http://www.cbsnews.com/video/watch/?id=7054210n

  32. Overuse of Groundwater • When groundwater supplies are depleted, the water table drops • Can cause many wells and springs to go dry

  33. 14.3 Groundwater and Geology Katchner Cavers, AZ

  34. Objectives • Explain how minerals become present in groundwater • Describe how groundwater deposits minerals • List three factors that can cause a spring to have a high mineral content • Describe the role that groundwater plays in the creation of caverns and karst topography

  35. Groundwater and Geology • By eroding and depositing rock minerals groundwater forms many distinctive geologic formations

  36. Mineral in Groundwater • When water evaporates it leaves behind impurities, therefore rainwater contains almost no dissolved mineral • Objective 1 - As groundwater seeps into soil and rock, it dissolves minerals that stay in the water. • Objective 3 - Type of rocks, distance groundwater travels underground, and the water’s temperature all effect the amount of minerals dissolved.

  37. Minerals in Groundwater • When groundwater contains large amounts of ions from dissolved minerals it is called hard water. • Calcium, magnesium, and iron ions found in hard water react with soap to form scum instead of suds. • Hard water can also leave deposits in pipes.

  38. Mineral Deposits by Groundwater • Geyser waters dissolve silica and deposit it on the surface. Creating a geyserite. • Petrified wood is formed when minerals dissolved in groundwater replace the decaying wood cells of buried trees. • Groundwater deposit also create the cement that holds sedimentary rocks together.

  39. Mineral Springs • Springs with a high concentration of mineral matter is called a mineral spring • Some of these spring areas have become health resorts (Hot Springs AK, Pagosa Springs, CO) • In desert regions alkali mineral springs may be poisonous. • Springs can also leave behind deposits. Calcite deposits are called travertine.

  40. Tonto Natural Bridge, AZ • It is believed to be the largest natural travertine bridge in the world. The bridge stands 183 feet high over a 400-foot long tunnel that measures 150 feet at its widest point

  41. Caverns • Limestone is a common bedrock that dissolves easily • When rainwater containing carbonic acid seeps into the ground limestone dissolves and forms caves. • Caves fill with water and slowly dissolves more limestone to create underground tunnels called caverns

  42. Caverns • When ground water drips from the roof of a limestone cave it slowly deposits calcite, creating stalactites • Underneath the stalactites where the water drips to the ground it forms stalagmites. • Sometimes stalactites and stalagmites meet to form columns.

  43. Karst Topography • In some regions, rainwater enters the ground through sinkholes. • Sinkholes are formed because carbon dioxide in the water has dissolved some of the rock beneath the surface. • Some sinkholes are shallow while others are deep enough to form ponds or lakes

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