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Conserving Groundwater

Objectives:

    1.    List the factors that affect a water budget.

    2.    Describe the results of overuse of groundwater.

    3.    Explain how groundwater becomes polluted.

    

Notes:

Roughly 50% of our drinking water currently comes from groundwater supplies.  It becomes more and more important to protect this resource as the population grows and our freshwater reservoirs recede.  Our conservation efforts are described by the water budget.

The water budget compares the amount of incoming water (recharge) to the amount of outgoing water (usage).  With all of the variables that affect the budget, weather is the controlling factor.  Other factors include:

Factors that contribute to discharge (usage)
human use
evapotranspiration
temperature
drought
Factors that influence recharge
land available to absorb the moisture
rain
duration
amount

time between rain

(waterknowledge.colostate.edu/ graphics/watbudg.gif)

(sofia.usgs.gov/publications/circular/ 1134/images/fig34th.gi)
Table 3. Preliminary estimates of natural water budget, in 1,000 acre-feet, for the lower east coast area, south Florida, 1980-89

[area, 5,814 square miles. From South Florida Water Management District, 1993]

Component Average annual
(Jan-Dec)
Wet season
(June-Oct)
Dry season
(Nov-May)
1980-81
(June-May)
1988-89
(June-May)
Rainfall 15,398 9,336 6,050 12,237 13,694
Evapotranspiration 11,729 5,668 6,024 11,359 11,285
Net groundwater outflow 298 150 151 274 289
Structure/tributary outflow 1,794 904 934 473 1,113
Structure/canal outflow 3,956 1,953 2,032 2,857 3,015
Wellfield pumpage 723 301 424 663 847
Net overland outflow 905 583 326 753 1,212
Changes in storage -338 +1,632 -1,937 -3,526 -1,971

 

When the water table rises we have a budget surplus.  An indication that a budget surplus may be present is when streams appear in the topography.   On the contrary, a deficit occurs as the usage is greater than the recharge.  In most populated areas we are in a deficit situation.  Factors contributing to overuse include:

over pumping of wells

can cause the water table to drop

may cause underground salinization of the aquifer rendering the pump unusable

compacting of soil over the subsided water table (subsidence)

reduces the porosity of the zone of aeration

additional causes are from the removal of oil from the land

  Reclamation efforts include:

allowing the water to enter drainage basins instead of being directed towards the sewer

water from sewers are being pumped back into holding ponds so it can be slowly reabsorbed 

Since recharging of the water takes place as rain seeps through the soil horizons, any polluting agent present is transported along with the water.  Pollutants include:

fertilizers

oil

farm wastes (nitrogen poisoning)

sewage from septic tanks and sewers

industrial wastes

diagram of potential pollution hazards, 21k GIF

www.gsi.ie/workgsi/groundwater/ karstbook/figures/fig11.gif)

 

 

 

 

 

 

 

Last modified: November 19, 2003