EFFECT OF CHANGING IRRIGATION DELIVERY SCHEDULES DURING PERIODS OF LIMITED AVAILABILITY OF WATER

Changes in crop patterns between design and operation of irrigation sy stems, often lead to conditions where water supply is no longer suffic ient to match demand. Managers of irrigation systems are then induced to modify the delivery schedules. In the case of an Italian pressurize d irrigation system, the on-demand delivery was modified into restrict ed frequency demand delivery during peak periods by introducing a 3-da y rotation among the sectors within an irrigation district. This chang e in delivery schedules has been evaluated for the years 1991 and 1992 by comparing the measured daily discharges withdrawn in two districts when operating on demand and on restricted frequency demand. Results show that this practice does not necessarily achieve water savings and , in certain conditions, demand and over-irrigation. (C) 1995 Silsoe R esearch Institute