Introduction to Basic Ground-Water Flow
 
By the earthDr!
 
DEWATERING THE WATER TABLE BY PUMPING GROUND WATER
 
The first figure is to illustrate the initial conditions before pumping starts. This figure is merely placed as
reference for comparison to the pumping condition of the second figure. A well is installed in a vertical orientation in the soil to pump ground water. Perforations are often made by cutting slots into the pipe at a right angle to the length of the pipe.

Ground water that seeps into the well screen (perforated pipe) can be pumped to the surface. When water is removed from a well, more ground water can seep through the slotted well screen replenishing those waters previously removed through pumpage. As water continues to seep through the well screen slots, the water level in the soil pores immediately surrounding the well are decreasing because there is now less water in the soil than before pumpage began. The soil immediately surrounding the well will not completely dry out, because there is gravity drainage of ground waters from the nearby, surrounding soils. The ground water levels are most depressed closest to the pumping well and least depressed farthest from the well. A steepening of the water table is depicted in the second figure due to removal of water from the well by pumpage and drainage of ground waters into the well from the nearby soils.

When we first start to pump a well, the water level in the well drops because the water isn't replaced fast enough by the water available from the surrounding soils.  There can be three impediments to flow of replacement water into the well:  there just  isn't sufficient water in storage within the soil pores; the rate of ground-water flow through the soil isn't sufficient to sustain the pumping rate; and/or the well screen is limiting to the seepage of water into the well.

The ground-water level is most depressed in the soil surrounding the well.  Obviously, water at a higher elevation will tend to flow to the depression of the water table caused by pumpage of ground water from the pumping  well.  This depression of the water table is illustrated in the figure to the left.

 
 
 
 
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