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Water Portal / Rainwater Harvesting / Groundwater recharge / Bunds

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{{Language-box|english_link=Water Portal / Rainwater Harvesting / Groundwater recharge / Bunds | french_link= Coming soon | spanish_link= Coming soon | hindi_link= वाटर पोर्टल / वर्षाजल संचयन / भूजल पुनर्भरण / पुस्ता या खेत-बन्धी | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= Coming soon | chinese_link=蓄水围 | indonesian_link= Pematang | japanese_link=堤防 }}__NOTOC__[[Image:bunds icon.png|right|80px]][[Image:Bund.JPG|thumb|right|350px200px| 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%2Fsmart20water%2520water%2520harvesting20harvesting.pdf&ei=NXNzT7CYEIiTiQKdxviYCw&usg=AFQjCNECS9O4gaRRQadp5dd4B5RDPxTwQA&sig2=QwWuUbra7my8Dpq5c_0baw ''Smart Water Harvesting Solutions]]][[Image:TrapezoidalBund.JPG|thumb|right|350px200px| 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.
{{procontable | proborder="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Can assist recharge of shallow wells <br>
- Can reduce salinity in groundwater <br>
- Reduces soil erosion <br>
- Higher crop returns in dryer years allow farmers to diversify income sources in normal years <br>
- The technology is simple to implement at the local level <br>
- Stone bunds (as opposed to other materials) do not readily wash away, so it is not vulnerable to unusual and variable intensity rainfall events. <br>| convalign= "top" | - High cost and effort involved in some earthworks, so poor or vulnerable families (e.g. single headed households) may struggle. A possible remedy: reduce donor dependency... use grain from harvests to pay off a loan that was used for the earthworks. Artificial glaciers in India were costing around $6,000 but it depends on the site. <br>
- Breached bunds will require repair work <br>
- Difficult to convince farmers of the gain to be had from using the techniques <br>
- Sedimentation within bunded areas means that bunds have to be regularly heightened <br>
- Popularity of the stone type of bund can result in shortages of stones, resulting in a higher cost for latecomers.<br>}|}
 ===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Lower crop yields. <br>
'''Underlying causes of effects''': Less water to crops from flooding. <br>
'''To increase resiliency of WASH system''': Drought-resistant & fast-growing crops; Diversify livelihoods of farmers.
 
More information on managing drought: [[Resilient WASH systems in drought-prone areas]].
====Floods====
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|350px200px| Contour stone bunding on a hillside. <br> Drawing: [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%2FSAI20Technical%2520Technical20Brief%2520Brief205%2520520%252020The%2520The20Importance%2520Importance20of%2520of20Soil%2520Soil20to%2520to20Water%2520Water%2520Use20Use.pdf&ei=gf91T6GYJ-jWiAK7zuGnDg&usg=AFQjCNFDyR4mjTVCcvvTt-9v4OrxAZQfDA&sig2=iMzgbW0eK395na_V_YA4Kw ''Water Conservation Technical Briefs.]]][[Image:stonebund.JPG|thumb|right|350px200px| Details of a stone bund.<br> Drawing: [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%2Fuploads20Technical%2FModules20Brief%2FLibrary205%2FSAI20%2520Technical20The%2520Brief20Importance%2520520of%252020Soil%2520The20to%2520Importance20Water%2520of%2520Soil%2520to%2520Water%2520Use20Use.pdf&ei=gf91T6GYJ-jWiAK7zuGnDg&usg=AFQjCNFDyR4mjTVCcvvTt-9v4OrxAZQfDA&sig2=iMzgbW0eK395na_V_YA4Kw ''Water Conservation Technical Briefs.]]] 
Local people should have a good degree of control in programme implementation, and the focus should be on appropriate techniques that can be operated and maintained using local resources. However, social/institutional constraints are not the only (or even primary) concern when building bunds – technical considerations are often overlooked. A few lessons learned are listed here which might apply generally:
* The erratic nature of rainfall intensity and lack of good rainfall data meant that designing bunds based on certain assumed runoff coefficients was difficult - sometimes runoff was vastly underestimated, and this was the reason for 90% failure rate of earthworks during the first 2 years of a large bund building programme where high runoff flows damaged bunds. Stone bunds (if stones are available) would work better.
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. * [http://www.fao.org/docrep/u3160e/u3160e00.HTM Water Harvesting: A Manual for the Design and Construction of Water Harvesting Schemes for Plant Production], FAO, Rome, 1991. * [http://www.fao.org/docrep/U3160E/u3160e07.htm#5.6%20trapezoidal%20bunds Water Harvesting Techniques], [http://www.fao.org/nr/nr-home/en/ FAO: Natural Resources Management and Environment Department]. * 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.
==Reference manuals, videos, and links==* [http://www.unep.orwashdoc.jpinfo/ietcdocsearch/publicationstitle/techpublications/TechPub-8a ''Sourcebook 169828 Smart Water Harvesting Solutions: Examples of Alternative Technologies innovative, low cost technologies for Freshwater Augumentation in Africa'']rain, United Nations Environment Programme (UNEP)fog, Division of Technology, Industry and Economics* [http://wwwrunoff water and groundwater.fao.org/docrep/u3160e/u3160e00.HTM ''Water Harvesting: A Manual for the Design and Construction of Water Harvesting Schemes for Plant Production''], FAO, Rome, 1991* (or [http://www.faoarcworld.org/docrepdownloads/U3160E/u3160e07.htm#5.6smart%20trapezoidal20water%20bunds ''20harvesting.pdf alternative link]) Netherlands Water Harvesting Techniques'']Partnership, Aqua for All, [http://www.fao.org/nr/nr-home/en/ FAO: Natural Resources Management and Environment Department].* Article: [http://tribune.com.pk/story/205714/pre-flood-warnings-four-bunds-could-develop-breaches/ Pre-flood warnings: Four bunds could develop breaches.] July 9Agromisa, 2011et al. The Express Tribune, Pakistan2007.
==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=9&ved=0CGsQFjAI&url=http%3A%2F%2Fwww.arcworld.org%2Fdownloads%2Fsmart%2520water%2520harvesting.pdf&ei=NXNzT7CYEIiTiQKdxviYCw&usg=AFQjCNECS9O4gaRRQadp5dd4B5RDPxTwQA&sig2=QwWuUbra7my8Dpq5c_0baw ''Smart Water Harvesting Solutions: Examples of innovative, low cost technologies for rain, fog, and runoff water and groundwater.''] 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%2FModules20Technical%2FLibrary20Brief%2FSAI205%2520Technical20%2520Brief20The%2520520Importance%252020of%2520The20Soil%2520Importance20to%2520of20Water%2520Soil%2520to%2520Water%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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