Riverbed infiltration galleries

Channels take water from a riverbed to a collector well in the riverbank. They are often screens (slotted or perforated pipes) that are inserted horizontally into a riverbed, but also infiltration galleries can be made from channels with graded gravel as long as sediments are not washed into the collector well. Where screens are used, the screen diameter tends to be larger than that used normally for jetted/driven wells.

Suitable conditions

• Infiltration galleries are often installed in shallow or fine sediment beds where there is poor permeability or lack of sand depth – in this case, the length proves to be advantageous.
• They can also be sited in areas where riverbanks are too high to allow manual or motorized suction pumps to operate.
• There should be water remaining in the riverbed throughout the dry season.
• Make it in a degrading river section where there is no deposition, so there are coarser grains and no silt deposits blocking flow.

Advantages	Disadvantages/limitations
- Allows a method of water extraction where sand depth is shallow or where sediments are fine and have low permeability - Cheap where it can be done without shuttering	- Difficult to make deep enough to ensure water at all times. Laying deeper galleries involves digging deeper and preventing sand trenches from collapsing by using shuttering – this becomes a more involved and expensive process - Significant amount of work involved - Difficult to construct where riverbanks are not alluvial (where rock breaking techniques required) - Can clog up over time