Water Portal / Rainwater Harvesting / Groundwater recharge / Bunds

Bunds (also called teras) are small barriers to runoff coming from external catchments (and possibly to a field where crops are to be grown). This plot of land is "bunded" on three sides, with the fourth side left open to capture runoff from an elevated area. Bunds slow down sheet flow on the ground surface and encourage infiltration (groundwater recharge) and soil moisture. The bunds consist of small stone or earthen walls constructed along the contour of a plot of land. Bunds also trap sediment and prevent erosion or land degradation. 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. 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.

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.

Teras show higher crop returns in dryer years and allow farmers to diversify income sources in normal years. In West Africa the technology is widely used in valley bottoms.