Groundwater and Wells

1
Groundwater and Wells

• Well is a hole bored into the zone of
  saturation and is the most common way of
  removing groundwater.

Reference Tarbuck and Lutgens text Pages
109 - 113
2
Groundwater and Wells

• In order to study wells, we must first
  investigate two terms Aqiufer and Aquiclude.

3
Groundwater and Wells
2) Aquiclude
impermeable layers such as clay and shale that
slow down or prevent water movement.
4
Surface Wells

• Wells act as reservoirs in which groundwater is
  stored.

• Some uses of water from wells are irrigation
  of farmland, industrial purposes, and drinking
  water.

• Water levels in wells are controlled by the
  position of the water table. The level of the
  water table depends on

1) Season (wet season and dry season)
2) Water withdrawal
5
Surface Wells
1) Season (wet season and dry season)

• Water table drops during the dry season and
  rises during the wet season. For this reason
  surface wells must be bored deep within the zone
  of saturation.

• Shallow wells may run dry if water table drops.

6
Surface Wells
2) Water withdrawal

• When water is pumped from the ground faster
  than it can be replenished, the water table
  drops in that area and a Cone of Depression
  results.

• Cone of depression is often found in areas
  where water is pumped for industrial uses and
  irrigation of farmland.

7
Artesian Wells
Water Recharge
Water Table (Pressure Surface)
Impermeable Aquiclude
Permeable Aquifer

• In artesian systems groundwater rises above the
  level where it was initially encountered.

Two conditions must exist

• Water must be within an inclined aquifer (Blue
  area) where one end is exposed at the surface
  where it can receive water.
• Impermeable layers (aquicludes) exist below and
  above the aquifer to prevent the water from
  escaping.

8
Artesian Wells
Water Recharge
Water Table (Pressure Surface)
Impermeable Aquiclude
Permeable Aquifer

• When the aquiclude above the aquifer is tapped
  (a hole drilled through), the weight of the
  water above will cause the water to rise up
  through the aquiclude where it tries to reach
  the water table or pressure surface.

• Same principle as a raised garden hose with a
  hole.

9
Sample Problem
With the aid of diagrams, explain the effect of a
drought on the water table.
Answer Water table lowers during a drought (dry
season) because the rate of withdrawal is greater
than the rate of recharge. Groundwater will move
out of the ground and in to streams and ponds.