A percolation pit, in its most low-tech form, is a simple hole dug into the ground. It facilitates groundwater recharge through infiltration of surface runoff into the soil or rock.

Differences to contour trenches:

  • Better water storage capability due to greater depth.
  • Better stability due to the circular walls, allows for application on steeper slopes than are recommended for contour trenches.[1]

For achieving a significant effect, several pits are placed across an area and are planted with appropriate plant species. Applied on a sufficient scale, this method can trigger reforestation – reviving perennial streams and creating springs along the way. In contrast to conventional reforestation, this does not involve planting a forest tree by tree; it merely helps nature across a threshold it can not (quickly enough) pass on its own.

The method was developed by Sachidanand Bhart. He adapted the old habit in his native region in the Himalayas of building a chal/khal – a 6-8m wide hole to conserve rain water for use in summers for fodder and animals – to the demands of reforestation around his home village.[2]

Field of application

Reforestation with percolation pits lends itself particularly well to steep terrain above human dwellings in a climate with irregular patterns of precipitation, where it increases water retention and reduces erosion. At the level of the dwellings, the gained groundwater can be utilised by complementing the system with larger retention basins and irrigation canals.[3]

Although the only publicised deployment appears to be in the Himalayas, the method should be adaptable to other areas – provided that the thickness of the soil and sediment layer is sufficient to dig holes.

Worldwide, there really is no shortage of hills and mountains suffering from runoff and erosion. Reestablishing forests as far upstream as possible is a smart thing to do; they will more easily spread downward than vice versa. All ecosystems located downstream will benefit from improved water supply and reduced peak water-levels during floods.

Implementation

Dimensions and layout

Pits are placed on the slopes, not along the drain lines that are moist anyway.[1] Starting with small 30 cm deep ones dug two meters apart just below the ridge,[3] sizes increase up to about 1.25 m in depth and diameter further downward[1] – with distances increasing as well.

Pictures and videos linked below in the References and External links sections give a good impression of the layout.

Plants

Planting grass immediately downhill of the pits secures their edges and prevents soil from being washed away.[1] That grass can be harvested as fodder,[4] regularly cutting it will also keep the sod dense and less prone to erosion.

Trees planted around the edges will benefit from water retained by the pit and in turn provide shade, stabilise the soil and increase its capacity to absorb water. Thereby, trees and the pit develop a mutually beneficial relationship.[1] Tree species selected should be adapted to the climate, i.e. usually local ones. Broad leaved trees are great for providing shade,[4] fruit and nut trees can be chosen to grow a food forest.

These at first distinct islands of vegetation will form the initial nuclei, more and more plants will "crystallize" around them until they merge and form a continuous ground cover.

Community support

To highlight the importance of community support and of keeping external stakeholders out of the game, a few quotes from Sachidanand Bhart:

Implementation isn’t that difficult but getting the support of the villagers to sustain this effort, is hard.[1]
The reason it has succeeded is simple. Education. No, not schools and

related education but education of the people. Creating awareness among

them and making them understand the benefits.[1]
Also, they knew I had nothing to gain. I was not getting paid for this.

This made it easier for them to trust me and to believe that I only had

their interests at heart.[1]
[...] I refused as I thought that if a flood of money comes in, then

our work will be washed away. The World Bank official sent a reply saying that after meeting you, I realised the India is the land of Gautam Buddha and of

Gandhi.[4]
Our work was based on people's hard work and a responsibility towards their forest. If money comes in, the feeling of responsibility would be lost.[5]

Local autonomy with regard to land use and water management is crucial. Once these rights are in dispute, people will not engage in such a long-term project.[6]

Case study

The method was developed and deployed in the Himalayas in and around the village Ufrenkhal (also Ufrain Khal,[7] Ufreikhal,[3] Uffrain Khal[5] or Ufrainkhal [OpenStreetMaps]) in the Pauri Garhwal district of the Indian state Uttarakhand.

Conditions

The village lies at an altitude of around 1900 m and receives a generous 1300 mm of rain annually,[4] although not regularly distributed over time.[8]

Once an abundant source of timber, the region's riches were exported on a large scale since the 1960s,[7] leaving a harsh terrain with scarce natural resources.[9] If any, government-planted pine forests are prevalent. Their roots, however, do not excel in preventing erosion and the pines easily catch fire.[4][5]

Scale and time frame

As of 2013, digging and planting started 35 years ago,[1] How many pits were dug is not all too clear, numbers given vary between 5,000[4] and 20,000.[5]

Results

The villagers have created "the best and thickest forests in the state",[7] thereby revived a perennial stream discharging 3 litres per minute near its source, along with countless springs. The water is used for irrigation and for drinking.[1]

Over 40 villages adopted the method.[1] Especially women are benefiting since it is mostly them managing home and fields while men are absent working in the plains.[7] Thanks to their lush forests, there is no need for them to collect firewood in other villages' forests any more.[5]

See also

References

Template:Reflist

External links

  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Cite error: Invalid <ref> tag; no text was provided for refs named create_river
  2. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named amazing
  3. ↑ 3.0 3.1 3.2 Cite error: Invalid <ref> tag; no text was provided for refs named profile
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Cite error: Invalid <ref> tag; no text was provided for refs named own_words
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Cite error: Invalid <ref> tag; no text was provided for refs named hindu
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named sisyphus
  7. ↑ 7.0 7.1 7.2 7.3 Cite error: Invalid <ref> tag; no text was provided for refs named dead_rock
  8. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named harvest
  9. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named celebrating
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