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Large-scale irrigation schemes have not yielded the expected outcomes in Sub-Saharan Africa. In Mauritania, average land productivity of rice schemes lies between 3 and 3.5tha⁻¹ and irrigated land has progressively being abandoned. At the same time, there is new international attention towards interventions in large-scale irrigation in the Sahel. Spatial and temporal variability of production are main causes of low productivity of large-scale irrigation schemes in Mauritania and threats to their sustainability. The present paper focuses on the performance of three representative large-scale schemes located along the River Senegal by analysing intra-scheme variability with respect to yield and irrigation intensity using field observations and satellite images. A sample of tertiary canals was selected in each irrigation scheme for weekly surveys of irrigation processes and maintenance. Yield measurement, irrigation (II) and harvest intensity (HI), indicators of irrigation adequacy (IIA) and drainage adequacy (IDA) constituted the basis of this analysis. Semi-structured interviews with the different actors at the various management levels (farmers; cooperatives; union of cooperatives; state irrigation agency; and the private service provider managing the water delivery in one of the schemes) were held in order to gain information on irrigation and drainage infrastructure, organisation and management of the schemes, financial aspects and irrigated surface. Within each irrigation scheme, a great variability was detected with respect to irrigation intensity and yield. Irrigation intensity could vary as much as from 0 to 1 whilst yield could range from 0.4 to 7tha⁻¹ in a single scheme. The analysis of water distribution patterns at scheme level indicated that variability in irrigation supplies and drainage were main sources of variability of yields and irrigation intensity. Physical, technical, and organisational factors underlie non-uniform water distribution patterns. The understanding of the origins of patterns of variability is a first step towards a more realistic assessment of schemes’ sustainability and contribution to food security.
