Short note: Infiltration wells

Infiltration wells are shallow, open, circular wells dug in the bed or bank of a river (or near a lake) in permeable sand and gravel, to collect water that has been filtered through the bed or bank material. They are sunk in a group and joined to a common sump (jack) well by horizontal pipes or by a gallery, and the water is pumped from the sump.

Construction

• Wells of 3 to 4.5 m diameter are lined with brick masonry with open joints or with concrete rings having perforations (weep holes) in the lower part.
• The bottom is usually left open (not sealed) and covered with a graded gravel layer, so that water enters through the bottom as well as the sides. The wells are sunk a few metres below the water level.
• The top is covered above the highest flood level, with a manhole for access.
• Several wells are located in a line, 20 to 30 m apart, and connected to the collecting well by porous or siphon pipes.

 river ~~~~~~~~~~~~~
 =========================  bank
  [W1]   [W2]   [W3]
    \     |     /   siphon/pipe
     \    |    /
       [Sump well] ---> pump

Features

• The water is cleaner and clearer than the river water because it is filtered by the bed and bank sand.
• The yield is moderate and depends on the permeability of the soil and on the river level.
• The wells are cheap to build, but clogging reduces the yield with time, so periodic cleaning or development is needed.
• Used for small town and rural supplies, mostly in the Terai and along rivers.