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  1. 1. Ground Water and Water Resources
  2. 2. Overview The supply of water available for use Groundwater aquifers examples of aquifers as resources Global distribution of water resources Pollution
  3. 3. Water Resources Very little of the earth’s water is available in a form directly utilizable by people; that is, as water resources. Most surface water resources come from surplus (SURPL) utilization Groundwater comprises a large percentage of freshwater resources
  4. 4. Groundwater Groundwater lies beneath the surface of the earth, but is affected by surface supply Groundwater is affected by changes to all of the earth’s spheres due to linkage through the hydrologic cycle Percolation
  5. 5. Groundwater Concepts Water percolates downward through permeable rock through the zone of aeration rock pores are unsaturated by water, many contain air Water then accumulates in the zone of saturation all rock pores contain water The water table is the upper surface of the zone of saturation its surface follows the contours of the ground above the water table controls the movement of surface water
  6. 6. Porosity describes the size, shape, arrangement, cementation, and compaction of subsurface material Permeable/Impermeable Whether or not a subsurface structure permits the flow of water Aquifer A layer of rock that is permeable to water flow in useable amounts unconsolidated aquifer: loose sand and gravel consolidated aquifer: porous rock, often sandstone or limestone Aquiclude A layer of rock that is impermeable to water flow in usable amounts
  7. 7. Confined Aquifer A layer of permeable rock between two impermeable layers An aquifer between two aquicludes Unconfined Aquifer An aquifer without an overlying aquiclude Perched Aquifer an aquifer created by a small aquiclude at a higher level than the water table
  8. 8. Intersections of the water table with the surface Springs: groundwater flows out of the ground Effluent streams: supplied by surrounding aquifer Influent streams: supply the local aquifer Artesian water Water in confined aquifers are under the pressure of their own weight, creating a pressure level (potentiometric surface), beneath this surface, water flows from the pressure of its weight
  9. 9. Aquifer recharge area Surface area where water enters an aquifer to recharge it. Differ for confined and unconfined aquifers Drawdown Lowering of the water table due to removal of water Occurs if rate of pumping or removal exceeds the horizontal flow of water in the aquifer Cone of depression The shape of the drawn down water table surrounding a well
  10. 10. Groundwater mining The act of removing water from an aquifer at a rate greater than its flow and recharge capacities Collapsing aquifers: water in aquifers often provide support for the porous rock, its removal could result in the rock collapsing, in which case the capacity of the aquifer is greatly reduced Seawater intrusion Contamination of an aquifer by seawater due to over-pumping the aquifer
  11. 11. High Plains Aquifer World’s largest known aquifer Charged from the meltwaters of retreating glaciers Only moderate precipitation today Heavy groundwater mining over the past 100 years, the last 50 especially 120,000 wells provide water for 14 million acres (170,000 wells in 1978), pumping 26 billion cubic meters of water per year Water table has dropped 30 meters over last 50 years, averaging a 2 meter drop per year since 1980. If mining stopped, it would take 1000 years to recharge Water used to irrigate grain crops (wheat, sorghum and corn, providing 40% of cattle feed) and cotton Projected: Half of the area (2/3 of Texas portion) destroyed by 2020.
  12. 12. The Middle East Groundwater supplies are rapidly being depleted Salt water incursion for tens of kilometers inland in Saudi Arabia Solutions: Desalinization plants 4000 in the world, 60% in Saudi Arabia Pipeline from Turkey
  13. 13. Global Water Resources Supply and demand for water are not evenly distributed over the world Supply is affected by climatic variability Demand is a product of: population (and growth) level of development agriculture relies on precipitation (PRECIP), augmented by irrigation (SURPL, ΔSTRG) industry relies more heavily on surplus water affluence accessibility Increased demand for water results in greater reliance on the utilization of surface and ground water (SURPL and STRG) can cause rivers to run dry (Colorado R., Yellow R.)
  14. 14. Pollution Groundwater flows at a slower rate than surface water Surface water contamination is quickly purged (elsewhere) Groundwater contamination is permanent and difficult to remediate Sources: industry, landfills, hazardous and toxic waste dumps, agriculture (herbicides, pesticides and fertilizer), septic tanks 10,000 suspected leaking gas tanks at service stations nationwide Surface water contamination concentrates pollutants downstream High cancer rates in New Orleans Dead Zone in Gulf of Mexico