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Groundwater Science, James Beach

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Groundwater Science, James Beach

  1. 1. Groundwater Science Aquifers Wells etc.James Beach, PGLBG-Guyton Associates
  2. 2. Special thanks to Robert Mace of TWDB for many slides
  3. 3. Outline• big picture• technical definitions (sorta)• flow in aquifers• pumping an aquifer• miscellaneous important stuff
  4. 4. Groundwater in the World From Freeze and Cherry (1979)
  5. 5. Major aquifers
  6. 6. Minor aquifers
  7. 7. Texas groundwater factoids• 60% of the water used in Texas• 81% of groundwater is used for irrigation• groundwater provides 39% of water to cities
  8. 8. groundwater use in Texas (1937 to 2003)
  9. 9. TECHNICAL DEFINITIONS
  10. 10. Definitions• Aquifer• Aquitard/confining layer• Vadose zone/unsaturated zone• Water table• Recharge• Water level• Unconfined aquifer• Confined aquifer
  11. 11. what is an aquifer?• an aquifer is geologic media that can yield economically usable amounts of water.
  12. 12. Porous Media
  13. 13. Hickory Aquifer, sandstone
  14. 14. Edwards-Trinity (Plateau) Aquifer, limestone
  15. 15. Ogallala Aquifer, sand and gravel
  16. 16. what is an aquitard?• an aquitard is geologic media that can not yield economically usable amounts of water.
  17. 17. what is a confining layer?• A confining layer is an aquitard that bounds an aquifer.
  18. 18. the unsaturated zone Unsaturated zone
  19. 19. the water table Unsaturated zone
  20. 20. recharge
  21. 21. recharge – typical
  22. 22. recharge – not typical
  23. 23. the water level
  24. 24. water flows down gradient(to lower potential energy)
  25. 25. Groundwater Flowpaths (TOP view)
  26. 26. Groundwater Flowpaths (SIDE view) Flat Ground LocalRegional SpringSprings With Hills and Topography
  27. 27. unconfined aquifer• An unconfined aquifer is an aquifer that is bounded by a confining layer at its bottom but not at its top.
  28. 28. an unconfined aquifer
  29. 29. confined (or “artesian”) aquifer
  30. 30. Flowing “artesian” well
  31. 31. Catfish Farm WellFlowed 24,000 gpm July, 1991
  32. 32. catfish farm wellEdwards aquifer• flowing well at 40,000 gpm• 1/4 of San Antonio’s use• 9% of Annual Recharge• world’s largest artesian wellNational Geographic (1993)
  33. 33. confined or unconfined?
  34. 34. confined or unconfined?
  35. 35. same aquifer: unconfined and confined
  36. 36. Major aquifers
  37. 37. same location: confined and unconfined aquifers
  38. 38. Confined/Dipping Aquifer Warning: Not to Scale
  39. 39. Confined/Dipping Aquifer
  40. 40. Edwards
  41. 41. Gulf Coast
  42. 42. Carrizo-Wilcox
  43. 43. Carrizo Aquifer
  44. 44. Leaky Aquifers Water Table is Higher Semi-Confined water level is lower
  45. 45. Why do you care?Unconfined Confined
  46. 46. FLOW IN AQUIFERS
  47. 47. fundamentals
  48. 48. what is permeability? hydraulic conductivity ? transmissivity?• Terms that describe the ease with which water flows through geologic media.
  49. 49. What determines flow? Flow = KA dh / dl• Hydraulic properties• Water level variation• Aquifer geometry
  50. 50. Trinity cross-section 2400 A 2200 Edwards Group 2000 1800 Upper Trinity aquifer 1600 SE model boundary 1400 Guadalupe Middle Trinity aquifer River Canyon 1200 Lake 1000 No flow 800 No flow A’ 600 Recharge Groundwater flow Edwards aquifer Pumping (BFZ) 400 Drain Cross-formational flow Spring flow 200 Surface water-groundwater interaction 0 5 10 15 misea level
  51. 51. water flows down gradient(to lower potential energy)
  52. 52. PUMPING AN AQUIFER
  53. 53. pumping a well: unconfined
  54. 54. pumping a well: confined Aquifer may not be depleted Pressure is decreased
  55. 55. what is storativity?• Storage properties describe the amount of water released from an aquifer when water level drops• Confined : “storativity”• Unconfined : “specific yield”
  56. 56. Storage yields from aquifers• Unconfined aquifers 0.01 to 0.3• Confined aquifers 0.005 to 0.00005
  57. 57. Simple regional flow (sand)
  58. 58. Simple regional flow + well
  59. 59. Drawdown caused by well
  60. 60. Drawdown caused by well
  61. 61. Groundwater movement to well After 50 years
  62. 62. Groundwater movement to well After 100 years
  63. 63. MISCELLANEOUS IMPORTANTSTUFF
  64. 64. Miscellaneous• spring and stream impact• droughts and groundwater• long-term impacts• water quality
  65. 65. Springflow Impact Edwards AquiferHigh correlation
  66. 66. • Observed springflow increase following several wet winter months
  67. 67. Outcrop Well Pumping Well Middle Wilcox or Simsboro Aquifer OutcropPage 71
  68. 68. Outcrop and Downdip Hydrographs in Brazos and Robertson Counties Outcrop WellDepth to Water (feet) Pumping Well State Well Number, Screened Interval Page 72
  69. 69. Total water level declines in the major aquifers
  70. 70. Water level declines800600400 Paluxy200 Woodbine 0 Lower Trinity-200 1880 1920 1960 2000 Year
  71. 71. Depth to Water (feet) 400 350 300 250 200 150 100 50 0 Jan-45 Jan-47 Jan-49 Jan-51 Jan-53 Jan-55 Jan-57 Jan-59 Jan-61 Jan-63 Jan-65 Jan-67 Jan-69 Jan-71 Jan-73 Jan-75 Jan-77 Jan-79 Jan-81 Jan-83 Jan-85 Jan-87 Jan-89 Jan-91 Jan-93 Jan-95Static Water Levels in Carrizo Aquifer Wells (Angelina and Nacogdoches Counties) Jan-97 Jan-99 Water Levels in Carrizo Wells
  72. 72. Water Quality ~40,000 wells Deep saline units not included
  73. 73. Water Quality Edwards Aquifer
  74. 74. Drought Sensitivity - Major
  75. 75. Minor
  76. 76. Drought and Groundwater• Most aquifers are drought tolerant• Higher than usual water level declines in drought can be caused by increased pumping• Important to discern between local short- term and regional long-term impacts
  77. 77. Take Home1. Laws of physics are constant – however – geology, aquifers and groundwater can vary significantly over short distances2. Good science is critical for developing appropriate rules and management3. Good science takes time and money

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