__NOTOC__{{Language-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 trenches trch icon.png|right|80px]][[Image:Contour_Trench_hillcontour_trench.JPG|thumb|right|350px200px| Contour trenches on a hillsidetrench 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.
===Suitable conditions===
* Locate trenches in natural runoff areas, but not on slopes over 10%.
* Soil in vicinity needs to have sufficient infiltration capacity and potential sub-surface storage capacity.
* In areas which have very heavy storms it may be dangerous to prevent the water completely from flowing down a slope. Build waterways or drains at a slight angle (1⁄2 degree - 1 degree) so that excess water is safely channeled away.
{{procontable | proborder="1" cellpadding="5" cellspacing="0" align="center"|-! width="50%" style="background:#efefef;" | Advantages! style="background:#f0f8ff;" | Disadvantages|-| valign="top" | - Facilitates recharge into surrounding ground which in turn improves soil moisture <br>
- Improves agricultural productivity and grazing potential as well as increases water for livestock and therefore mitigates against drought <br> - Reduces soil erosion <br>
- Can assist recharge of shallow wells <br>
- Prevents pollutants from draining into water bodies <br>
- Gully plugs: no trench design required, just uses existing gully drainage pattern <br>
| convalign= "top" | - Recharge of groundwater is not certain according to local sub-surface conditions (geological layers blocking infiltration) <br>
- Trenches silt up and will need maintenance <br>
- Lack of understanding by landowners about advantages of contour trenches; difficult to convince them during the first year to give their land for trench construction <br>
- Costly and in-depth analysis of hydrology/runoff gullies <br>
- Recharge capacity/permeability information is needed, which is difficult to get if no in-depth rainfall data is available <br>
- Expensive cost of implementation where mechanical excavating machinery is used<br>|}}
===Resilience to changes in the environment===
====Drought====
'''Effects of drought''': Lower crop yields. <br>
Contour trenches specifically help control flooding and capture water from floods. If rain event is expected to be massive, plant vegetation along the outer edge of the contour to stabilise the trenches and prevent erosion.
===Construction, operations and maintenance===[[Image:Contour_Trench.JPG|thumb|right|300px200px|An example of contour trench in Kitenden, Vietnam. <br> Source: Westerveld Conservation Trust]]
In order to efficiently capture runoff in a catchment through appropriately sized trenches, the following information and analysis is needed:
* Catchment area, gathered from topographical maps
* Involvement of local people in the design of the project ensures that their participation continues.
===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.
* Labour: 1.5m3 per person per day manual earth movement.
===Field experiences===
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.sswm.info/sites/default/files/reference_attachments/PRAMANA%202007%20The%20Design%20of%20Contour%20Trenches%20in%20Vietnam.pdf The Design of Contour Trenches in Vietnam] Copyright by Kharis Erasta Reza Pramana Delft, The Netherlands, October 2007.
==Reference manuals, videos, and links==* Manual: [http://www.googlebebuffered.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCUQFjAA&url=http%3A%2F%2Fcitg.tudelft.nl%2Ffileadmin%2FFaculteit%2FCiTG%2FOver_de_faculteit%2FAfdelingen%2FAfdeling_watermanagement%2FSecties%2Fwaterhuishouding%2FLeerstoelen%2FWaterbeheer%2Fonderzoek%2FProjects%2FMsc_Research%2FCompleted%2F500_2005-2009%2Fdoc%2FKERP_Master_Thesis_Reportdownloads/sussman_contour_trenches.pdf&ei=IqhzT5jaCavs2AWy66T1Dg&usg=AFQjCNEDhvxYmEh7FJHIudcrGjPZwcB13Q&sig2=Y0Zz_BdLBGu0PoFBSN6qLg The Design of Manual: Contour Trenches in Vietnam] Copyright by Kharis Erasta Reza Pramana Delft, The Netherlands, October 2007- Using the "A" frame and how to make a contour trench.
* ManualLarge wiki on water use for agriculture: [http://wwwweb.googlearchive.comorg/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CC4QFjAA&url=/20151025174729/http%3A%2F%2Fwww://agropedia.bebufferediitk.com%2Fdownloads%2Fsussman_contour_trenchesac.pdf&ei=e6t0T7O6FMqRiALI26zDCQ&usg=AFQjCNF_0jYbzUhQaxznk2DZGMjztGnG7Q&sig2=uhbWzb4fop2OXOofo721mA Design Manualin: Contour Trenches80/ Agropedia] - Using the "A" frame and how to make a contour trench.
===Acknowledgements===* CARE Nederland, ''Desk Study : [[Resilient WASH systems in drought -prone areas]].'' October 2010.* Sussman, Daniel. [http://www.googlebebuffered.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CC4QFjAA&url=http%3A%2F%2Fwww.bebuffered.com%2Fdownloads%2Fsussman_contour_trenchesdownloads/sussman_contour_trenches.pdf&ei=e6t0T7O6FMqRiALI26zDCQ&usg=AFQjCNF_0jYbzUhQaxznk2DZGMjztGnG7Q&sig2=uhbWzb4fop2OXOofo721mA ''Design Manual: Contour Trenches'']. Bren School of Environmental Science and Management, University of California Santa Barbara. 2007.* [http://www.googlewashdoc.cominfo/docsearch/title/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 ''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.