Chapter Fifteen Groundwater

1. Chapter FifteenGroundwater

2. Groundwater • Earth’s hydrosphere extends from top of atmosphere to ~ 10 km (6 mi) below the Earth’s surface. Groundwater, 0.6% of world’s water, accounts for 97% of Earth’s supply of unfrozen water. • Surface waters from rivers, lakes or precipitation enter the ground under the influence of gravity • The amount of water that enters the ground depends on the topography, geologic composition and vegetation • The surface water will percolate downwards until it reaches a zone where all the pore spaces are saturated with water

3. Factors affecting infiltration

4. Moisture through tree

5. Surface distribution of water

6. Movement and Distribution of GW • Water bound to clay minerals • Zone of aeration: unsaturated zone • Zone of Saturation • Water Table: Upper surface of the zone of saturation • Capillary Fringe: Lower part of the aeration zone – range from few tens of cm to several meters

7. Groundwater Movement • For groundwater to flow- need porous and permeable materials • Porosity is the percent of pore spaces in relation to the total soil/rock/sediment volume (Primary Porosity: Porosity that develops as a rock forms; Secondary Porosity: Develops after a rock has formed) • Permeability is a measure of the ability of rock/sediment to transmit fluid • Groundwater flow occurs when there is a hydraulic gradient • Hydraulic conductivity is the ability to transmit groundwater. Typical groundwater flow is slow ~0.5 – 1.5 cm/day (0.2 - 0.6 in/day). The slow movement stores the water making it available to humans.

8. The subsurface distribution of water

9. Primary porosity of sedimentary rocks

10. Pore connection and Permeability

11. Pore connection and Permeability – contd.

12. Hydraulic gradient

13. Variations in water table depth

14. Water Table configuration

15. Perched water pools

16. Tapping Groundwater aquifer • Groundwater depth is a reflection of local topography and prevailing climate • Aquifers are permeable water-bearing bodies of geologic materials • Unconfined and Confined aquifers • Aquiclude and Aquitard • Artesian flow- water flows to the surface from wells without pumping • Potentiometric surface • Natural Springs • Geysers- intermittent surface emission of hot water/steam

17. How groundwater flows • Groundwater flow potential • Gravity • Pressure from overlying water and rocks • Hydraulic Gradient: Difference in potential / distance • Hydraulic conductivity: Measure of conductivity – size, shape & degree of sorting of its grains – coarse, well-rounded, well-sorted and gravel – high conductivity • Darcy’s principle (19th Century): Rate at which water flows is a difference in potential a hydraulic conductivity

18. Groundwater flow – contd. • Mesuring the Rate of GW Flow: • Dye injection method • Carbon –14 dating method Groundwater Flow Rate: Average: 0.5 to 1.5 cm/day Fastest: 100 m / day

19. Composite Landscape

20. Artesian aquifer

21. Desert Oases

22. Municipal water tower

23. Natural springs

24. Natural springs – contd.

25. Geysers

26. Locating groundwater and features associated with pumping • Locating Groundwater • Mapping • Water table from well records, lake, river levels, drilling test holes • Features Associated with Pumping • Cone of depression- local depression in water around pumping well • Subsidence- compressed land due to aquifer depletion • Salt water intrusion- due to over pumping along coast line • Greater demand for water- leads to groundwater depletion and introduction of pollutant • Solutions- enhance recharge, water transfer, conservation, desalinization, and use of iceberg

27. Search for Groundwater • Characteristics of the Water Table: • Depends on Typical depth • Relationship to topography • Response to Climatic Fluctuations AQUIFERS: • Aquifer: Permeable, water-bearing bodies of geological material • Unconfined aquifer: Not overlain by impermeable cap tock • Confined Aquifer: Found in greater depths, between aquiclude (impermeable rock layers) and Aquitard

28. Search for water

29. Overuse of groundwater

30. Water table around a well

31. The effect of development on a water table

32. Subsidence in a coastal area

33. Subsidence in a coastal area – contd.

34. Groundwater contamination / purification • Natural occurring solutes- Chlorine, Arsenic, Mercury, and Selenium • Manufacturing contaminants- from household products: cans of paint, solvent, cleanser etc. • Natural Groundwater Purification • Filtration- adhere to clay particles • Decomposition- some decompose completely by oxidation • Bacteria action- organic solids consumed by microorganis

35. Saltwater intrusion

36. Salt water intrusion – contd.

37. Stratigraphy of Yucca Mountain

38. Landfill sites

39. Landfill sites – contd.

40. Products of Groundwater • Karsts • Water reacts with carbon dioxide to form weak carbonic acid which then attacks limestone • H2O + CO2 => H2CO3 + CaCO3 => Ca++ HCO3– • Caves- natural underground cavities and most common geological product of limestone dissolution • Cave deposits- spelotherms are deposits on cave surfaces in a variety of forms: travertine, Stalactite, Stalagmite, banded draperies or drip curtains • Growth of spelotherm- depends on the solution and porosity of surface material, climate, topography, and vegetation

41. State 1 of cave formation

42. State 2 of Cave formation

43. Stalactite, stalagmite and travertine

44. Cave formation

45. Speleothem growth and climate

46. Rise and fall of sea level

47. Karsts Topography Surface expression of the geology of dissolved limestone and work of near surface water • Cave and Karsts landscapes are extremely sensitive- so need to be protected • Landform • Sinkholes-circular surface depression • Disappearing Streams- flow through sinkholes may emerge as spring several kilometers away • Natural Bridge- series of neighboring sinkholes expand and join together

48. Worldwide distribution of karst landform

49. Typical landforms associated with karst topography