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Groundwater. Importance of Groundwater. Supplies 40\% of U.S. public drinking water. Almost all rural residents Agriculture can be dependent on groundwater for irrigation. Shapes the land surface (e.g. sinkholes, mudslides). Fig. 17.3. Occurrence of Groundwater.

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importance of groundwater
Importance of Groundwater
  • Supplies 40% of U.S. public drinking water.
    • Almost all rural residents
  • Agriculture can be dependent on groundwater for irrigation.
  • Shapes the land surface (e.g. sinkholes, mudslides).

Fig. 17.3

occurrence of groundwater
Occurrence of Groundwater
  • Found everywhere below the surface, in all rock/sediment types.
  • Stored in and flows through pores spaces.

Fig. 17.5

Fig. 17.5

occurrence of groundwater1
Occurrence of Groundwater
  • The watertable is the boundary between the unsaturated and saturated zones.

Unsat. – pores filled with air and water

Sat. – pores filled with only water

Fig. 17.6

occurrence of groundwater2
Occurrence of Groundwater
  • Most surface water bodies (i.e. streams, lakes) occur where water table insects the land surface.

Quarries/mines must be dewatered while operating.

Fig. 17.4

movement of groundwater
Movement of Groundwater
  • Precipitation infiltrates, flows through unsat. zone to water table.
  • Groundwater flows from higher to lower elevations (velocity – cm to m per day).

Fig. 17.17

water table fluctuations
Water Table Fluctuations
  • The water table is continually rising and falling.
    • rises when precipitation infiltrates
    • falls as water discharges to streams

Fig. 17.13

water table fluctuations1
The water table also drops when water is pumped from wells.Water Table Fluctuations
  • Shallow wells go dry during dry periods.
  • water table drops below bottom of the well.
effects of pumping groundwater1
Effects of Pumping Groundwater
  • Groundwater can be pumped out faster than it recharges.
    • water table drops, aquifer yields less water

Fig. 17.13

effects of pumping groundwater2
Effects of Pumping Groundwater

Fig. 17.14

  • High Plains Aquifer:
    • Low recharge rate
    • High pumping rate (agriculture)
    • Max. water table drop is >50 m (160 ft.)
    • Half of aquifer has been drained
effects of pumping groundwater3
Effects of Pumping Groundwater

Fig. 17.33

  • Land subsidence:
  • Water in pores supports grains, resists compaction.
  • Dewatering pores allows compaction.
  • Compaction lowers land surface elevation (subsidence).
effects of pumping groundwater4
Effects of Pumping Groundwater
  • Land subsidence fissures in Arizona caused by groundwater pumping.

Fig. 17.15

effects of pumping groundwater5
Effects of Pumping Groundwater

Fig. 17.33

  • Salt water intrusion:
  • Near coasts, groundwater at depth is salty.
  • Pumping fresh water may eventually draw salt water into a well.
groundwater and landscapes
Groundwater and Landscapes
  • Limestone is easily dissolved by groundwater.
  • Sinkholes – where surface rocks collapse into the void left after limestone dissolves.

Fig. 17.36

groundwater and landscapes1
Groundwater and Landscapes
  • Groundwater flows along joints, dissolves limestone.
  • Eventually, caves form and sinkholes form when cave roof collapses.

Fig. 17.36

groundwater and landscapes2
Groundwater and Landscapes
  • Sinkhole damage in Florida.
groundwater and landscapes3
Groundwater and Landscapes
  • Areas in the U.S. where rocks are easily dissolved.

Fig. 17.36