Avricultural water management

Agricultural Water Management 40 (1999) 101±105

The failure of adjustable irrigation technology, the options for change and the consequences for research
Lucas Horst1
Department of Irrigation and Soil & Water Conservation, Wageningen Agricultural University, The Netherlands

Abstract In response to the increasing awareness of the failings of the water division technology in many irrigationschemes, the options for changes in technology are discussed in the light of trends in water resources development. This leads to possible agendas for research. # 1999 Published by Elsevier Science B.V. All rights reserved.
Keywords: Flow regulation; Irrigation; Water division technology

1. Introduction Most irrigation systems in Asia, Africa and Latin America are designed to regulate andmeasure the flows at each point in the system, and are equipped with adjustable water division structures to achieve this, However, these structures require large numbers of trained staff for their operation and are often so complex that farmers have difficulty in knowing whether the flows are delivered according to the principles of allocation. Not surprisingly, these systems have for decades beendogged by a multitude of problems, including low performance, conflicts between farmers and management, farmers interfering with their operation, damaging of structures, illegal off-takes and corruption. Systems of this type continued to be designed during the last 50 years, while attempts were made to solve the problems by improving the management environment: restructuring management, training,organising farmers, etc. Only recently has the technology of adjustable structures been explicitly questioned. For example, Plusquellec et al. (1994), p. 5: ``Extended gravity irrigation schemes with manually operated gates and control structures rarely work, despite all efforts to improve irrigation management
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L. Horst / Agricultural Water Management 40 (1999) 101±105

and the capacity of staff'' and Burns (1993), p. 784: ``The myth of the efficient and equitable flow of valuable water, by gravity, from source through a large-scale public system of raised earth aqueducts presided overby an honest and competent bureaucracy manipulating thousands of gates continuously for just-on-time delivery to the root zones of plants needs to be discarded first.'' 2. Options for change There are three categories of water division technology:  adjustable technology  automatic technology  simplified technology Having recognised the failure of adjustable technology, two options remain open.2.1. Automation In the last decade, a number of experts have advocated introducing automation, i.e. systems controlled automatically, either hydraulically (by float-operated gates) or electronically, electro-mechanically, by microprocessors or computers. Fewer persons are generally required to operate and maintain such systems, but they must be highly skilled. Knowledge of computers, electronicsand mechanics is often essential. Apart form this staffing requirement, a more problematic constraint lies in the available water supply. Automation can generally only be implemented in projects in which unrestricted water demand is met by sufficient supply throughout the year. This technology is, therefore, unsuitable for run-of-the-river projects or for projects with restricted reservoircapacity. 2.2. Simplification Simplification can be obtained in two ways:  Allowing extra water for a less complicated delivery schedule ± additional operational requirements (AOR) (Meijer, 1992) ± results in simple operation and simple technologies: fixed (proportional division) or open±closed structures or modulator Á outlets (e.g. Neyrpic's module a masque). At first sight, AOR appear to have...