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Water Portal / Rainwater Harvesting / Groundwater recharge / Bunds

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[[Image:bunds icon.png|right|80px]]
[[Image:Bund.JPG|thumb|right|200px| Near a bund wall. Photo courtesy of [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CGsQFjAI&url=http%3A%2F%2Fwww.arcworld.org/downloads/smart%2Fdownloads%2Fsmart%2520water20water%2520harvesting20harvesting.pdf&ei=NXNzT7CYEIiTiQKdxviYCw&usg=AFQjCNECS9O4gaRRQadp5dd4B5RDPxTwQA&sig2=QwWuUbra7my8Dpq5c_0baw ''Smart Water Harvesting Solutions]]]
[[Image:TrapezoidalBund.JPG|thumb|right|200px| Shape of a trapezoidal bund system with slope direction down. <br> Drawing: [http://www.fao.org/docrep/U3160E/u3160e07.htm#5.6%20trapezoidal%20bunds FAO: Water Harvesting.]]]
'''Bunds ''' (also called teras) are small barriers to runoff coming from external catchments (and possibly to a field where crops are to be grown). Bunds slow down water sheet flow on the ground surface and encourage infiltration (groundwater recharge) and soil moisture. There are different types of bunds. A rectangular type, where land is "bunded" on three sides, with the fourth side left open to capture runoff from an elevated area and a contour type, where bunds are created in rows along the contour of a hillside. The bunds consist of small stone or earthen walls. A small channel on the inside of the bunds is made to let the water run along. Excess water drains along the tips of the outer arms (rectangular type). These spillways may improve the efficiency and reduce maintenance costs of the teras. The base bund can be 50-300 meters long, while the arms are usually 20-100 meters long. Bunds are not generally built to eventually extract water, but rather to add soil moisture or contribute to groundwater recharge.
Bund design has to be adjusted according to local conditions. They can vary in design and include non-enclosed systems (e.g. trapezoidal bunds where water escapes around the edges), and enclosed systems (e.g. bunded fields where water enters via a channel and escapes from a spillway in the bund once the field is flooded). In certain site-specific examples, they are used to create small artificial glaciers which helps release melt water slowly, so as to adjust to short sowing seasons.
In West Africa the technology is widely used in valley bottoms.
===Suitable conditions===
* Locate bunds in natural runoff areas, preferably in sites already shaped by topography – indicators include seeing where water flows during flood times, and soil / vegetation types. The key is to approach each site individually and to work with natural topographical features – experience in the area will influence the design.
===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Lower crop yields. <br>
When a region with bunds floods, strengthen the existing bunds by raising them several feet, otherwise breaches are possible. This is especially important when bunds are used to protect crops or urban/residential areas.
===Construction, operations and maintenance===
[[Image:contourStonebund.JPG|thumb|right|200px| Contour stone bunding on a hillside. <br> Drawing: [http://www.saiplatform.org/uploads/Modules/Library/SAI%20Technical%20Brief%205%20%20The%20Importance%20of%20Soil%20to%20Water%20Use.pdf Water Conservation Technical Briefs.]]]
[[Image:stonebund.JPG|thumb|right|200px| Details of a stone bund.<br> Drawing: [http://www.saiplatform.org/uploads/Modules/Library/SAI%20Technical%20Brief%205%20%20The%20Importance%20of%20Soil%20to%20Water%20Use.pdf Water Conservation Technical Briefs.]]]
Stone bunds: There is limited, ongoing repair required as the stones are not vulnerable to erosion. However, silting behind the stone bunds requires that the stones to be relaid from time to time. Care must be taken that overtopping of the bunds does not lead to erosion on the downstream face, with subsequent gully formation and undercutting of the bund.
===Costs===
* Where stones are in short supply, there are increased costs associated with their acquisition and transport.
* Labour for construction: 6-16 days per hectare. Annual maintenance: 3-18 days per hectare.
* If bunds are formed in a terrace-like design, the labour required for construction is estimated at 150 to 350 person days/ha for terraces and cut off drains. The cost of these structures is approximately $60-460/ha.
==Field experiences== ==Manuals, videos, and links===
* [http://www.unep.or.jp/ietc/publications/techpublications/TechPub-8a Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa] or ([http://www.washdoc.info/docsearch/title/115176 alternative link]). United Nations Environment Programme (UNEP), Division of Technology, Industry and Economics.
* ARTICLE: [http://tribune.com.pk/story/205714/pre-flood-warnings-four-bunds-could-develop-breaches/ Pre-flood warnings: Four bunds could develop breaches.] July 9, 2011. The Express Tribune, Pakistan.
* Large wiki on water use for agriculture: [http://web.archive.org/web/20151025174729/http://agropedia.iitk.ac.in:80/ Agropedia] ===Acknowledgements===
* CARE Nederland, Desk Study: [[Resilient WASH systems in drought-prone areas]]. October, 2010.
* [http://www.washdoc.info/docsearch/title/169828 Smart Water Harvesting Solutions: Examples of innovative, low cost technologies for rain, fog, and runoff water and groundwater.] (or [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0CGsQFjAI&url=http%3A%2F%2Fwww.arcworld.org/downloads/smart%2Fdownloads%2Fsmart%2520water20water%2520harvesting20harvesting.pdf&ei=NXNzT7CYEIiTiQKdxviYCw&usg=AFQjCNECS9O4gaRRQadp5dd4B5RDPxTwQA&sig2=QwWuUbra7my8Dpq5c_0baw alternative link]) Netherlands Water Partnership, Aqua for All, Agromisa, et al., 2007.
* Rufino, L., [http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CFkQFjAB&url=http%3A%2F%2Fwww.saiplatform.org/uploads/Modules/Library/SAI%2Fuploads%2FModules%2FLibrary%2FSAI%2520Technical20Technical%2520Brief20Brief%25205205%252020%2520The20The%2520Importance20Importance%2520of20of%2520Soil20Soil%2520to20to%2520Water20Water%2520Use20Use.pdf&ei=gf91T6GYJ-jWiAK7zuGnDg&usg=AFQjCNFDyR4mjTVCcvvTt-9v4OrxAZQfDA&sig2=iMzgbW0eK395na_V_YA4Kw Water Conservation Technical Briefs: TB 2 – Rainwater Harvesting and Artificial Recharge to Groundwater]. Sustainable Agriculture Initiative (SAI). August, 2009.
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