__NOTOC__ <small{{Language-title box|english_link=Water Portal />Rainwater Harvesting / Groundwater recharge / Contour trenches | french_link= Coming soon | spanish_link= Trincheras de contorno | hindi_link= वाटर पोर्टल / वर्षाजल संचयन / भूजल पुनर्भरण / समोच्च-कंटूर खत्तियाँ | malayalam_link= Coming soon | tamil_link= Coming soon | korean_link= Coming soon | chinese_link=等高沟 | indonesian_link= Parit kontur | japanese_link= 水のポータル サイト / 雨水貯留 / 地下水涵養 / 等高線濠}}
[[Image:contour trch icon.png|right|80px]]
[[Image:contour_trench.JPG|thumb|right|200px| Contour trench under construction and measuring contours with hose pipes. Photo: WTC.]]
At its simplest, '''contour trench ''' construction is an extension of the practice of plowing fields at a right angle to the slope. Contour trenches are ditches dug along a hillside in such a way that they follow a contour and run perpendicular to the flow of water. The soil excavated from the ditch is used to form a berm (a narrow shelf) on the downhill edge of the ditch. The berm can be planted with permanent vegetation (native grasses, legumes) to stabilize the soil and for the roots and foliage in order to trap any sediment that would overflow from the trench in heavy rainfall events.
Contour trenches are not irrigation channels, rather they are used to slow down and attract runoff water, which then infiltrates into the soil. Small scale contour trenches can also be used within field level. The water that infiltrates can be used as soil moisture for crops cultivated after a rainfall event, directly for pumped irrigation, or extracted from shallow wells in the area.
===Costs===
* In Vietnam, after trenches were completed farmers were discussing ways to access low-cost loans with long-time repaymentconditions so that they could replicate the technology. Access to finance therefore seems to be important in scaling up this technology.
* Cost of excavation in Vietnam was around 1,000 Euro per hectare.
* Materials: US$2.6/m3 or US$4,100/ha.
Experience from Vietnam showed that in 5 out of 7 shallow wells that were near the trenches with water tables of between 3 and 18 metres below ground level, showed an increase in water levels after rainfall events of over 60mm because of infiltration from the contour trenches. It seems that recharge of groundwater is not certain according to local sub-surface conditions – in Vietnam, water levels in 2 out of the 7 wells near the trenches were unaffected. This is probably due to certain geological layers blocking infiltration. So it is always a possibility that trenches will not affect water levels.
[http://web.archive.org/web/20151019103949/http://www.ektitli.org/2011/11/21/successful-water-conservation-in-awalkhed-village-nasik/ Successful Water Conservation in Awalkhed Village, Nasik.]
===Manuals, videos, and links===
* Manual: [http://www.bebuffered.com/downloads/sussman_contour_trenches.pdf Design Manual: Contour Trenches] - Using the "A" frame and how to make a contour trench.
* 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.
* Sussman, Daniel. [http://www.bebuffered.com/downloads/sussman_contour_trenches.pdf Design Manual: Contour Trenches]. Bren School of Environmental Science and Management, University of California Santa Barbara. 2007.
* [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.arcworld.org/downloads/smart%20water%20harvesting.pdf alternative link]) Netherlands Water Partnership, Aqua for All, Agromisa, et al. 2007.
