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Groundwater exploration

resistivity survey seismic survey, vertical distribution of gw

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Groundwater exploration

  1. 1. GroundwaterGroundwater
  2. 2. Hydrogeology Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) It is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers).
  3. 3. The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation.
  4. 4. • PrecipitationPrecipitation andand infiltrationinfiltration contribute tocontribute to groundwatergroundwater, which is stored, which is stored in underground reservoirsin underground reservoirs until it surfaces as a spring oruntil it surfaces as a spring or is drawn from a drawn from a well.
  5. 5. Infiltration:Infiltration: • process of waterprocess of water moving into themoving into the soil/groundsoil/ground • to penetrate,to penetrate, enter or gainenter or gain accessaccess
  6. 6. I. Water Beneath the SurfaceI. Water Beneath the Surface Groundwater:Groundwater: underground waterunderground water that fills almost all of thethat fills almost all of the pores/voidspores/voids in rocks andin rocks and sedimentsediment
  7. 7. AquiferAquifer:: a body ofa body of rockrock that can storethat can store water and also let water flow throughwater and also let water flow through
  8. 8. Think of an AQUIFERAQUIFER as a… • large, horizontal spongesponge that absorbs and transports water along its length
  9. 9. An aquifer is an underground layer of water- bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well. It is porous & permeable to the extent of maintaining a steady supply of sufficient amount of water to the wells or springs.
  10. 10. Occurrence of Groundwater in different terrains – •Weathered – pore spaces & voids/openings •Hard and Stratified rocks – cracks & fractures
  11. 11. Aquifer types • Aquifer • Aquiclude • Aquitard • Aquifuge Unconfined aquifer Confined aquifer( artesian) Perched
  12. 12. Aquifer : A saturated, permeable, geologic unit / formation or group of formations that can yield a significant amount ( sufficient quantity) of groundwater to be called as a source of supply. Aquiclude :A saturated geologic unit which yields inappreciable quantity of water to drain & through which there is inappreciable movement of water. Aquitard : A saturated, permeable, geologic unit / formation or group of formation which yield water in appreciable quantity to drain completely to an aquifer but through which appreciable leakage of water is possible. Aquifuge : A formation that does not store any water.
  13. 13. Unconfined
  14. 14. Unconfined aquifer • Ground water possesses a free surface open to the atmosphere • • Upper surface of the zone of saturation is called water table
  15. 15. Confined
  16. 16. Confined aquifer( artesian) • It is one in which ground water is confined under pressure by overlying & underlying aquitard or aquicludes. • Water level in wells rises above the top of the aquifer
  17. 17. Potentiometric Surface or Piezometric surface Represents the areal variation of the head of an aquifer
  18. 18. ad
  19. 19. City water systems can be considered to be artificial artesian systems.
  20. 20. ParametersParameters  Porosity  Permeability Specific yield & retention Transmissibility and Storage Coefficient
  21. 21. porosity Porosity “n” is the ratio of the voids to the total volume of an unconsolidated or consolidated material percentage of open spaces in a rock or sediment
  22. 22. Porosity:
  23. 23. FACTORS THAT INFLUENCEFACTORS THAT INFLUENCE POROSITY:POROSITY: (a) SORTING: amount of uniformity in particle size HIGH pore space LOW pore space
  24. 24. (b) SHAPE:(b) SHAPE: rounder particles = more porous (c) PACKING:(c) PACKING: loosely packed = more porous
  25. 25. Permeability: It is the property by virtue of which the rock/ geological formation allows water to travel through its pore spaces or other openings
  26. 26. 2. Permeability: how freely water flows through open spaces in a rock (the pores must be connected) Impermeable – water can NOT flow through
  27. 27. It is the measure of the quantity of water passing through a unit cross section in a unit time & 100 % hydraulic gradient.
  28. 28. Can something be porous butCan something be porous but impermeable?impermeable? • The cork end isThe cork end is red because thered because the grape juice wentgrape juice went into it. Does thisinto it. Does this mean it is porous?mean it is porous? • If you turn theIf you turn the bottle upside downbottle upside down will it leak? Is thewill it leak? Is the cork permeable?cork permeable?
  29. 29. A permeable rock is always porous but a porous rock may not always be permeable Porosity & permeability depend on width of fracture, frequency, distribution & orientation .
  30. 30. Fine grain sediments have the tendency to hold up water against the force of gravity Coarse grained well sorted sediments yield water readily In case of consolidated rocks, dimensions of secondary openings, joints, cavities largely control the specific yield. Specific retention depends on total interstitial surface in the rock.
  31. 31. B. Zones of GroundwaterB. Zones of Groundwater 1.1. Zone of Saturation:Zone of Saturation: the layer ofthe layer of ground where all the pores areground where all the pores are filled with water.filled with water.
  32. 32. 2.2. Water Table:Water Table: upper surface ofupper surface of the zone of saturationthe zone of saturation
  33. 33. 3.3. Zone of Aeration:Zone of Aeration: upper region,upper region, where water is both in the soil andwhere water is both in the soil and seeping down to the water table.seeping down to the water table.
  34. 34. Zone of Aeration ►
  35. 35. • Capillary Action: ability of water to rise UP the soil. • Smaller particle size = greater capillarity
  36. 36. Capillary Fringe:Capillary Fringe: middle layer,middle layer, between the water table and thebetween the water table and the zone of of aeration.
  37. 37. C. MOVEMENT OFC. MOVEMENT OF GROUNDWATERGROUNDWATER • Depends on: 1. Permeability of the aquifer • ↑ permeability = ↑ velocity 1. Gradient of the water table • Gradient = steepness of the slope • ↑ gradient = ↑ velocity
  38. 38. II. Wells and SpringsII. Wells and Springs • Water Table:Water Table: upper layer of rocksupper layer of rocks with all pores filled with water.with all pores filled with water.
  39. 39. A. Ordinary Well:A. Ordinary Well: A hole dugA hole dug below the water table which fillsbelow the water table which fills up with water.up with water.
  40. 40. Cone of Depression:Cone of Depression: lowered arealowered area of the water table due to pumpingof the water table due to pumping
  41. 41. B. Artesian Wells: water flows freely with no pumping • Underground water under pressure (between two impermeable rock layers) rises to the surface • Water is naturally filtered as it passes through porous rock and seeps to
  42. 42. III. Groundwater andIII. Groundwater and Chemical WeatheringChemical Weathering A.A. Caverns:Caverns: rocks rich in calciterocks rich in calcite (limestone) slowly dissolved(limestone) slowly dissolved by carbonic carbonic acid. • Hard water = many dissolvedHard water = many dissolved minerals (Ca, Mg, Fe)minerals (Ca, Mg, Fe) • Soft water = few dissolvedSoft water = few dissolved mineralsminerals
  43. 43. Luray Caverns, VA
  44. 44. • Formation of a CaveFormation of a Cave
  45. 45. 1. Stalactites:1. Stalactites: water withwater with dissolved calcite runs from adissolved calcite runs from a cave’scave’s ceilingceiling and solidifiesand solidifies downward.downward.
  46. 46. 2. Stalagmites:2. Stalagmites: calcite richcalcite rich water drips on the cave’swater drips on the cave’s floorfloor and builds upward.and builds upward.
  47. 47. If the twoIf the two connect,connect, then itthen it forms aforms a columncolumn..
  48. 48. 3. Natural3. Natural Bridge:Bridge: when thewhen the roof of a cavernroof of a cavern collapses incollapses in several placesseveral places leaving an arch-leaving an arch- shaped rock.shaped rock.
  49. 49. B. KARST TOPOGRAPHYB. KARST TOPOGRAPHY • regions where chemical weathering by groundwater is now visible at the surface • regions where it is humid and there are limestone formations near the surface • Virginia, Kentucky, Tennessee, Indiana, and Florida have Karst Topography
  50. 50. 1. Sinkholes1. Sinkholes (the main feature(the main feature of Karst Topography)of Karst Topography)
  51. 51. How do sinkholes form?How do sinkholes form? • Rain seeps through soil and absorbsRain seeps through soil and absorbs carbon dioxide and reacts with decayingcarbon dioxide and reacts with decaying vegetationvegetation • Acidic water is createdAcidic water is created • Water moves through spaces and cracksWater moves through spaces and cracks undergroundunderground • Limestone is slowly dissolved, creatingLimestone is slowly dissolved, creating network of cavities and voidsnetwork of cavities and voids • Pores and cracks enlargePores and cracks enlarge • Land surface above collapses or sinksLand surface above collapses or sinks
  52. 52. 2. Streams that disappear in2. Streams that disappear in the groundthe ground Like Lewis Creek in Staunton
  53. 53. 3. Caverns and Caves3. Caverns and Caves
  54. 54.