Contour ridges, sometimes called contour furrows or micro watersheds, are used for crop production. Ridges follow the contour at a spacing of usually 1 to 2 metres. Runoff is collected from the uncultivated strip between ridges and stored in a furrow just above the ridges. Crops are planted on both sides of the furrow.
The yield of runoff from the very short catchment lengths is extremely efficient and when designed and constructed correctly there should be no loss of runoff out of the system. Another advantage is an even crop growth due to the fact that each plant has approximately the same contributing catchment area.
==Suitable conditions==
This low cost technology has the potential to increase food security in below normal rainfall years.<br>
The relatively low planting density discourages farmers, especially in a good year, and the technique does not work well on steep slopes.
Contour ridges are limited to areas with relatively high rainfall, as the amount of harvested runoff is comparatively small due to the small catchment area.
==Construction, operations and maintenance==
[[Image:ContourRidgeDrawing.JPG|thumb|right|300px| Contour ridge in Kenya. Photo: SAI.]]
The overall layout consists of parallel, or almost parallel, earth ridges approximately on the contour at a spacing of between one and two metres. Soil is excavated and placed downslope to form a ridge, and the excavated furrow above the ridge collects runoff from the catchment strip between ridges. Small earth ties in the furrow are provided every few metres to ensure an even storage of runoff. A diversion ditch may be necessary to protect the system against runoff from outside.
Ridges need only be as high as necessary to prevent overtopping by runoff. As the runoff is harvested only from a small strip between the ridges, a height of 15 -20 cm is sufficient. If bunds are spaced at more than 2 metres, the ridge height must be increased.
The cultivated area is not easy to define. It is a common practice to assume a 50 cm strip with the furrow at its centre. Crops are planted within this zone, and use the runoff concentrated in the furrow. Thus for a typical distance of 1.5 m between ridges, the C:CA ratio is 2:1; that is a catchment strip of one metre and a cultivated strip of half a metre. A distance of 2 metres between ridges would give a 3:1 ratio. The C:CA ratio can be adjusted by increasing or decreasing the distance between the ridges.
Minimal maintenance is required if the ridges are properly constructed initially. Maintenance involves reconstruction of any lines and ridges that might have collapsed.
==Reference manuals, videos, and links==
* [http://www.fao.org/docrep/U3160E/u3160e07.htm 5.Water Harvesting Techniques.] FAO.
==Acknowledgements==
* 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%2Fuploads%2FModules%2FLibrary%2FSAI%2520Technical%2520Brief%25205%2520%2520The%2520Importance%2520of%2520Soil%2520to%2520Water%2520Use.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.
