Infiltration galleries include horizontally laid screens (slotted or perforated pipes, typically 75-300mm PVC) in a river bank or river bed. Water flows from the sediment into the drainpipe and from there into a collector well in the river bank. Typical yields are about 15L/min/meter screen.
Size - from a few meters to 1-2 km – defines costs. In Kenya, a 72m of PVC pipe of 160mm PVC pipe may cost about USD1,200. Additional costs include construction and maintenance expenses for the extraction well in the river bank.
Infiltration galleries can be implemented from small community-scale to a larger user group level. It can be managed either by a community committee or another local authority. Since maintenance is minimal, institutional requirements are limited.
Location is important as surface water source contaminations may increase the need for purification and construction affects people downstream. Animal husbandry or municipality should be downstream from construction to avoid organic contamination. Upstream activities can still be source of contamination.
Installation at least at 1.5m below ground surface and still 1m within saturated zone during dry season. Installation includes: excavating trench, laying gravel layer, pipe and gravel covering, filling the trench again. Occasionally, pipe can clog and needs cleaning.
The extracted surface water is likely to be contaminated. Lack of central water purification necessitates household-level treatment/disinfection. Social friction is possible if level of water extraction significantly reduces available water downstream.
No relevant remarks for Infiltration galleries and drains.
Akvopedia - Riverbed infiltration galleries
SSWM - Bank Filtration
WHO - Infiltration galleries