Integrated Performance Assessment of the Gezira Irrigation Scheme

Technical, Agricultural, Institutional, and Socio-economic Perspectives

Abstract

The Gezira Scheme (GS) is considered one of the oldest irrigation systems in Africa and the Arab region. Moreover, it is the largest scheme (0.9 million ha) in the world under a single management. The irrigation network is 11,000 km long with 29,000 field channels. This paper evaluates the performance of the GS irrigation system after a century of operation, particularly given the serious deterioration over the past two decades, during which the system has failed to meet crop water requirements. The assessment draws on MOIWR sediment monitoring and desilting records for 1987-2005, HR Wallingford field measurements, and published technical efficiency and hydro-economic studies. This issue may be primarily attributed to the significant amounts of sediment entering the scheme each year and the mismanagement of the irrigation system. Inflowing sediment concentration rose from about 700 ppm in the 1930s to about 8,000 ppm in the 1990s; desilting now consumes more than 60% of O&M expenditure; and the scheme's debt grew from USD 34 million in 1999 to over USD 150 million by 2005. The consequence of this situation is water shortage in many areas of the scheme, while others experience flooding, leading to inequitable water distribution. This disparity leads to a decline in crop production and returns from the scheme. In light of these issues, a critical review of the irrigation system is warranted. The concept and procedure for designing and remodelling the silted canals to restore the original section are highlighted, based on the rich experience and performance of this irrigation system. It is concluded that aquatic weeds increase sedimentation, and the deposited sediment enhances aquatic weeds' growth, thereby reducing canal capacity. The impact of this on the socio-economic development of the scheme inhabitants is explained. The paper finally examines the possibility of maintaining stable regime conditions in the canals. It also reports on the future of irrigation system management and the possibility of achieving an efficient and effective system to improve crop production.