Water Portal / Rainwater Harvesting / Groundwater recharge / Contour ridges

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.

Suitable conditions

Contour ridges for crop production can be used under the following conditions:

• Field from flat up to 5.0%.
• Field Rainfall 350-700 mm.
• Area with rills or ondulations should be avoided.

The distance between the ridges should be adapted depending on rainfall amount.
This low cost technology has the potential to increase food security in below normal rainfall years.
The relatively low planting density discourages farmers, especially in a good year, and the technique does not work well on steep slopes.

Construction, operations and maintenance

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.

Minimal maintenance is required if the ridges are properly constructed initially. Maintenance involves reconstruction of any lines and ridges that might have collapsed.

Costs

With human labour, an estimated 32 person days/ha is required. Using machinery, the time requirement is reduced, but the costs are increased to an estimated US$100/ha. This technology is considered low cost, although the rate of its adoption has not been high.

Acknowledgements

• Rufino, L., Water Conservation Technical Briefs: TB 2 – Rainwater Harvesting and Artificial Recharge to Groundwater. Sustainable Agriculture Initiative (SAI). August 2009.