Dependent irrigation systems in Southeast Asia: Complication for irrigation performance improvements

Canal irrigation systems in Southeast Asia are being examined with a view to improving their performances. Some systems of medium size may, with their drainage water, be supporting small irrigation systems unknown to officials of water and land development agencies. With a decision to modify the water flow pattern of a medium-size system, the administrators who plan the modifications should learn whether such dependent systems occur. This paper suggests that dependent systems are more likely to have been created on gently sloping land cut by gullies and small, locally deep valleys than on land without such valleys. It also suggests that aerial photographs, satellite images, maps, and government records may not provide information on the locations of the systems, and that such information be sought instead from farmers.