Draw a neat diagram showing different types of aquifers. Indicate and explain the various types of wells that result from these aquifers?


AquifersAquifers are divided into two types:

  1. Unconfined
  2. Confined

An unconfined aquifer is often shallow, and the vadose zone above it primarily contains permeable material. The top of the aquifer is the water table. The water table moves up and down on a seasonal basis. It is highest during the wet season owing to higher recharge and lower pumping rates (e.g., no irrigation), and lowest during the dry season because of limited recharge and higher use (e.g., a high rate of irrigation).

Confined aquifers may be shallow or deep, and are characterized by being separated from the surface by low-permeability strata (e.g., geologic layers) that confines the groundwater below it. In a confined aquifer, groundwater is generally under pressure. This water pressure may vary seasonally, similar to the water table in an unconfined aquifer.

Because groundwater in a confined aquifer is under pressure, it will rise in a well bore above the level of the aquifer penetrated by that well. One way to visualize this is to squeeze a milk or juice pouch that is punctured at the top by a straw. If the straw fits firmly into the squeezed pouch, the liquid will rise up into the straw, above its level inside the pouch.

Artesian and flowing artesian wells are typical of wells drilled into confined aquifers. An artesian well is one in which the groundwater rises above the level of the penetrated aquifer. The water in an artesian well will rise to an elevation at which the pressure of the water in the aquifer is matched by the pressure reflected by the elevation of the water in the well; this level is known as the hydrostatic level. If groundwater reaches all the way to the surface under its own pressure, the well is called a flowing artesian well.

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