Surface Irrigation

• Water is delivered to the field from a canal, pipe outlet, or pump, without pressurised distribution across the field itself
• In basin irrigation, water floods a level, bunded area and infiltrates as it stands
• In border irrigation, water flows down a graded strip bounded by low ridges
• In furrow irrigation, water flows along shallow channels between crop rows (covered separately as its own method)
• Infiltration continues as water advances and, where applicable, recedes across the field

Surface irrigation suits fields that are level or can be economically graded, and it is closely associated with rice, where basin (paddy) flooding is integral to production, as well as with cereals and sugarcane grown under long-established canal irrigation systems. It is generally less practical on steep or highly uneven land without significant earthworks.

Surface irrigation efficiency varies widely depending on field levelling precision, the length of run, and management skill: a well-designed and well-managed system can perform reasonably well, while poor levelling or oversized fields often lead to uneven infiltration, with some areas over-watered and others under-watered.

Precision land levelling (including laser levelling), shorter field lengths, and careful control of inflow and cutoff timing are practices used to improve the uniformity and efficiency of surface irrigation.

Field preparation is central to surface irrigation performance: basins and border strips must be levelled and bunded to a consistent grade, and furrows or borders need periodic reshaping as they erode or fill in over time and between tillage operations.

• Laser or GPS-guided land levelling improves surface uniformity and reduces ponding or dry patches
• Field size and shape are matched to available flow rate so water can advance across the whole area in a reasonable time
• Tailwater (runoff from the low end of the field) may be collected and reused in some systems to reduce losses

Because water moves and ponds across the surface, surface irrigation on poorly drained or heavy soils can contribute to waterlogging and, over time in some settings, to secondary soil salinity if drainage is inadequate. Field preparation and maintenance — levelling, bunding, and channel upkeep — represent an ongoing labour or capital requirement.