[[Image:Bund.JPG|thumb|right|400px350px| Near a bund wall. Photo courtesy of [http://www.google.com/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 ''Smart Water Harvesting Solutions]]][[Image:TrapezoidalBund.JPG|thumb|right|400px350px| Shape of a trapezoidal bund system with slope direction down.]]
Bunds (also called teras) are small barriers to runoff coming from external catchments (and possibly to a field where crops are to be grown). Bunds slow down water sheet flow on the ground surface and encourage infiltration (groundwater recharge) and soil moisture. There are different types of bunds. A rectangular type, where land is "bunded" on three sides, with the fourth side left open to capture runoff from an elevated area and a contour type, where bunds are created in rows along the contour of a hillside. The bunds consist of small stone or earthen walls. 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 (rectangular type). 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. Bunds are not generally built to eventually extract water, but rather to add soil moisture or contribute to groundwater recharge.
==Construction, operations and maintenance==
[[Image:contourStonebund.JPG|thumb|right|400px350px| Contour stone bunding on a hillside.]][[Image:stonebund.JPG|thumb|right|400px350px| Details of a stone bund.]]
Local people should have a good degree of control in programme implementation, and the focus should be on appropriate techniques that can be operated and maintained using local resources. However, social/institutional constraints are not the only (or even primary) concern when building bunds – technical considerations are often overlooked. A few lessons learned are listed here which might apply generally:
* The erratic nature of rainfall intensity and lack of good rainfall data meant that designing bunds based on certain assumed runoff coefficients was difficult - sometimes runoff was vastly underestimated, and this was the reason for 90% failure rate of earthworks during the first 2 years of a large bund building programme where high runoff flows damaged bunds. Stone bunds (if stones are available) would work better.