__NOTOC__{{Language-box|english_link= Water Portal / Rainwater Harvesting / Groundwater recharge / Infiltration wells | french_link= Coming soon | spanish_link= Coming soon | hindi_link= वाटर पोर्टल / वर्षाजल संचयन / भूजल पुनर्भरण / रिसन-इन्फिल्ट्रेशन कुंए | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= Coming soon | chinese_link=渗井 | indonesian_link= Coming soon | japanese_link= Coming soon }}[[Image:infiltration wells.png|right|80px]][[Image:InfiltrationWell.JPG|thumb|right|250px200px|Infiltration well in Madagascar. Eric Fewster, BushProof.]]__NOTOC__ Also called interception wells, these '''infiltration wells''' are shallow wells which put (or draw ) water into (or from ) a natural aquifer outside of a riverbed, but which have a partial lining. They can be used to either drain a catchment area or recharge groundwater, especially where recharge of the aquifer is low due to low rock/soil permeability (the well penetrates through this). Infiltration wells do not have to have a direct inlet (although they can have one). Without an inletWater extraction, they can become a larger hole and be filled with porous natural materials to increase the ground's infiltration capacity andhowever, in most cases, have is a coiled drain between the soil surface and the underground piping. Rockssecondary activity, coarse wood chips or straw can be used as filtering material. Wells made of straw are constructed like permeable trenches and do not have a coiled drain, which can limit their infiltration capacity. Water extraction can the water levels will be done with [[Handpumps]] or [[Small lower and efficient motor pumps]]. Handpump cylinders the amount extracted will need to physically be able to fit inside the screen that has been installedmore limited.
Infiltration wells do not have to have a direct inlet (although they can have one). Without an inlet, they can become a larger hole and be filled with porous natural materials to increase the ground's infiltration capacity and, in most cases, have a coiled drain between the soil surface and the underground piping. This coiled drain is perforated to allow water inside where it can flow more quickly out of the drain. It acts as a security for high rainstorm runoff events that might rain too much water to effectively infiltrate into the well or aquifer. Rocks, coarse wood chips or straw can be used as filtering material. Wells made of straw are constructed like permeable trenches and do not have a coiled drain, which can limit their infiltration capacity. Water extraction can be done with [[Handpumps]] or [[Small and efficient motor pumps]]. Handpump cylinders will need to physically be able to fit inside the screen that has been installed. ===Suitable conditions===
* Site where water table is within 5 metres of ground surface, and where soils are stable.
* Site where water demand is low, e.g. for small communities.
For medium size sand with an average porosity, the distance equivalent to 25 days is around 30 metres, but this can increase to over 100 metres for coarser sediments. However, the distance from contamination to water intake can reduce significantly where the screen intake is at a sufficient depth – this is due to greater variation of aquifer properties in vertical directions than lateral, meaning that a borehole with handpump could be placed very close to a latrine with low risk. However, screen depth must increase with increased extraction rate.
{{procontable | proborder="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Lower cost than making a fully lined well due to less lining needed <br>
- Speedier construction compared to fully lined well <br>
- Good for low-yielding aquifers<br>
- Since it's a lower tech option, villagers can participate easier, therefore less supervision required<br>
| convalign= "top" | - Not much water is available for extraction (as compared with a traditional well)- Cannot easily access intake for maintenance or in case of problems<br>
- No possibility to line as you dig, therefore more safety concerns if soil is not stable<br>
}|}
===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Less recharge of aquifer due to less rainfall; Increasing population & water demand; Size of aquifers – e.g. limited sand volume; Wells not sunk deep enough into water table; Incorrect siting; Graded gravel around pipe not correctly done.
'''To increase resiliency of WASH system''': Increase volume through construction of groundwater dam; Sink wells/pipes deeper; De-water wells during caissoning within the water table; Construct during the latter half of the dry season; Site in riverbeds that are dry for part of the year, where water remains in the riverbed throughout the dry season; Increase flow by use of porous concrete & perforated pointed steel pipes driven horizontally into the aquifer (riverbed wells) and graded gravel (infiltration galleries & jetted wells); Site in a degrading river section where there is no deposition (infiltration galleries); Put graded gravel around pipes to minimize clogging and increase flow.
More information on managing drought: [[Resilient WASH systems in drought-prone areas]]. ===Construction, operations and maintenance===
'''General advice on cement''': A common cause of cracks in structures and linings (e.g. in tanks, dams, waterways, wells) is errors in mixing and applying the cement. First of all, it is important that only pure ingredients are used: clean water, clean sand, clean rocks. The materials have to be mixed very thoroughly. Secondly, the amount of water during mixing needs to minimal: the concrete or cement needs to be just workable, on the dry side even, and not fluid. Thirdly, it is essential that during curing the cement or concrete is kept moist at all times, for at least a week. Structures should be covered with plastic, large leaves or other materials during the curing period, and kept wet regularly.
'''Specific advice''':====Construction====[[Image:StrawInfiltrationWell.jpg|thumb|right|300px200px|Infiltration well filled with straw. <br> Source : Georges Lamarre (MAPAQ)]]
* Construction involves digging a hole to the water table in stable soil that has no risk of collapsing. Digging should not go deeper than 5 metres for safety reasons.
* Digging continues inside the water table but due to the low yield of the aquifer, digging can proceed only without buckets for de-watering purposes.
====Rock or wood chip infiltration wells====
[[Image:WoodChipInfiltrationWell.jpg|thumb|right|300px200px|Infiltration well filled with rock or wood chips - soil not tilled. For more options like this see [httphttps://www.googleagrireseau.comnet/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.agrireseau.qc.ca%2Freferences%2F6%2FFiches_MAPAQreferences/6/Fiches_MAPAQ-AAC_Erosion%2FPuitsdInfiltration_EN_web/PuitsdInfiltration_EN_web.pdf&ei=2OiFT6SyH5HJiQKPpoXmDQ&usg=AFQjCNHB9NNqUldcGONNvh-vZjj2chsjQA&sig2=aX6lmpw7gCOou3UhFHg0RQ Infiltration wells Factsheet].]]
A hole measuring 1 to 1.5 m in diameter and approximately 1 m deep is excavated at the location selected for the infiltration well.
If the well is constructed with rock in sandy or loamy soil, the bottom and sides of the excavation can be covered with a geotextile membrane (of the Texel 7609 or 7612 type). This membrane will prevent lateral clogging by the rock and is attached to the drain with drainage adhesive tape where the drain crosses it. The membrane is cut 30 cm below the surface of the soil if the soil is to be tilled above the well once installation is complete. Otherwise, the membrane can extend up to the soil surface. Note that no geotextile membrane is used in wood-chip wells.
Where the erosion rate is high and the risk of clogging is significant, it is preferable that the soil above the infiltration well not be tilled. A minimum radius of 3 m around the well is therefore grassed over to filter the soil particles and create a buffer zone between the tilled soil and the infiltration well. The well can also be covered with rock (e.g. clean 100- mm rock) to finalize the installation.
'''Permeability of some types of rock (meters/day)'''<br>
{|border="1" cellpadding="5"
|-
! scope="col" |Type of rock
! scope="col" |Permeability
(m/d)
|-
|gravel
|100 - 1000
|-
|mixed sand and gravel
|50 - 100
|-
|coarse sand
|20 - 100
|-
|fine sand
|1 - 5
|-
|fractured or weathered rock
|0 - 30
|-
|sandstone
|0.1 - 1.0
|-
|clay
|0.01 - 0.05
|-
|shale
|negligible
|-
|limestone
|negligible
|-
|solid rock
|negligible
|}
====Maintenance====
Lastly, infiltration wells and separate drain outlets must be inspected frequently to evaluate the condition of the structures as well as their efficiency in improving surface drainage and reducing erosion problems.
==Costs== ==Field experiences== ==Reference manualsManuals, videos, and links===* Video: [http://youtuwww.beindiawaterportal.org/Ywarticles/well-revival-effort-sees-many-nySGtZzM Infiltration wells other- An overview (English)benefits Well revival effort sees many other benefits]]. Pan Himalayan Grassroots Development FoundationA community drive to revive wells in Mokhla talab near Udaipur results in water security for longer periods of time as well as making leaders out of women.* Video: [http://youtu.be/FTmw2mlXIv0 Infiltration wells - Construction details (Hindi), Part 1]www. Pan Himalayan Grassroots Development Foundationindiawaterportal.* Video: [http:org/articles/youtu.be/ERwDsMHN_Vg Infiltration experiments-community-wells Experiments with 'community wells - Construction details (Hindi)'] Mobilized farmers in Dhule, Maharashtra, Part 2]. Pan Himalayan Grassroots Development Foundationshow how communities can use groundwater as a common resource in an organised and collective manner.* [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.agrireseau.qc.ca%2Freferences%2F6%2FFiches_MAPAQ/references/6/Fiches_MAPAQ-AAC_Erosion%2FPuitsdInfiltration_EN_web/PuitsdInfiltration_EN_web.pdf&ei=2OiFT6SyH5HJiQKPpoXmDQ&usg=AFQjCNHB9NNqUldcGONNvh-vZjj2chsjQA&sig2=aX6lmpw7gCOou3UhFHg0RQ Infiltration wells Factsheet]. Agriculture and Agri-Food Canada (AAFC) and the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec (MAPAQ).* [http://www.samsamwater.com/library/Artificial_groundwater_recharge_for_water_supply_of_medium-size_communities_in_developing_countries.pdf ARTIFICIAL GROUNDWATER RECHARGE FOR WATER SUPPLY OF MEDIUM-SIZE COMMUNITIES IN DEVELOPING COUNTRIES.] E.H. Hofkes and J.T. Visscher. December, 1986.
===Acknowledgements===* CARE Nederland, ''Desk Study : [[Resilient WASH systems in drought -prone areas'']]. October 2010.* [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.agrireseau.qc.ca%2Freferences%2F6%2FFiches_MAPAQ/references/6/Fiches_MAPAQ-AAC_Erosion%2FPuitsdInfiltration_EN_web/PuitsdInfiltration_EN_web.pdf&ei=2OiFT6SyH5HJiQKPpoXmDQ&usg=AFQjCNHB9NNqUldcGONNvh-vZjj2chsjQA&sig2=aX6lmpw7gCOou3UhFHg0RQ Infiltration wells Factsheet]. Agriculture and Agri-Food Canada (AAFC) and the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec (MAPAQ).