Irrigation systems in Sri Lanka

Water requirement for rice cultivation in Sri Lanka is fulfilled through rainfall or irrigation.

When rainfall  is satisfactory to meet the water requirement during the season, crop is raised completely as rainfed. Crop acquires water directly from the rain or from seepage and run off from surrounding areas. There are no channels for distribution of water. Dykes are constructed and maintained to retain water and to prevent water leakages from the field.

In areas where adequate rainfall is not assured, supplementary irrigation is provided through distributary channel systems from tanks and anicuts. These irrigation networks essentially designed for rice cultivation are divided into two main categories based on command area namely

(1) Minor irrigation systems

• • Command and area is less than 80 ha
  • Both tank and anicut systems are included
  • Come within the justification of Department of Agrarian Development
  • As command area is comparatively smaller and distances of distributary channels  are shorter, a better  regulation can be expected
  • Water availability depends on the catchment area, rainfall tank capacity and the size of command area

(2) Major irrigation systems

• • command areas greater than 80 ha,
  • Both tanks (reservoir) and anicut systems
  • Come within the justification of either the Irrigation Department of Mahaweli Authority
  • Tanks and streams which are used for anicut systems depend on their own catchments for water in many systems
  • For some tanks, water is diverted from other catchments through trans-basin channels, by which water supply is more assured than the tanks which depend on their own catchments
  • Distributor channel systems are better equipped with control structures than in the minor irrigation schemes and  controlled water management practices have been introduced.
  • Water is issued mostly on a pre-scheduled rotation