Canal irrigation at night

Abstract

Most canal irrigation water in South and Southeast Asia and elsewhere continues to flow at night and much is badly used or wasted. Yet what happens to water at night is a neglected subject, a matter for anecdotes more than analysis. Darkness, cold, fear, normal working hours, and desire for sleep deter irrigation staff, farmers and labourers from activities at night. At the farm level, irrigation at night entails extra labour and costs. It requires smaller streamflows and well shaped fields. Paddy and trees are the easiest crops to irrigate, and younger, lower and more thinly spread crops are usually easier than those which are older, taller and denser. On the lower parts of main systems, control at night often passes informally from irrigation staff to irrigators. Potential productivity of water at night is slightly raised by lower evaporation losses, but this gain is negligible compared with losses from breaks in channels, inefficient water application, and wasted water flowing into drains. Reuse of night drainage water lower down sometimes makes waste less wasteful than it appears. Equity effects at night are mixed: some farmers poach at the expense of others, but some get water at night who are denied it during the day. Night irrigation increases costs and inconvenience to small farmers, but raises labourers' incomes. Flooding and waterlogging can result from uncontrolled water flows at night. Practical implications are of two types: a)reducing irrigation at night, especially where water can be saved and stored by regulating releases from main reservoirs; in storage or by travelling in canals; by use of intermediate reservoirs; by pondage on-farm; or as groundwater. Care is needed in analysing what is waste and what is water saved. b)improving irrigation at night — by making flows predictable and manageable; by improving convenience and efficiency including lighting, ease of movement and field shaping; by choosing easy crops; by zoning for night flows; and by phasing for short nights, warmth and visibility. The potential for better performance on canal irrigation systems is probably large. It is hoped that this paper will encourage and provoke system managers, designers and researchers to explore the practical potential of this neglected subject about which much more needs to be known. Canal irrigation at night is too important to remain a blind spot any longer. B.C. Punmia & Pande Brij Basi Lal,Irrigation and Water Power Engineering, 7th ed., 1983, p. 48 The magnitude of waste involved in not irrigating at night is so huge that savings from other sophistications in the field of water management like the lining of watercourses etc. pale into insignificance. S.P. Malhotra, 1983. Night irrigation and what we know about it is truly a blank page in our books. Gabriel J. Tibor, 1985.