Sustainability of rainwater harvesting in enhancing water productivity in various biophysical and socioeconomic conditions of SSA is a key in large scale livelihood improvement. A study was undertaken in Makanya catchment of rural Tanzania to assess sustainability of storage type of rainwater harvesting systems including microdam, dug out pond, sub-surface runoff harvesting tank and rooftop rainwater harvesting system. The increasing population in upstream areas of the catchment has forced use of RWH systems for streams and river water abstraction. The agricultural intensification in hillslopes has affected the water availability for downstream uses. Rainfall variability, runoff quality and quantity, local skills and investment capacity, labour availability and institutional support influence sustainability of rainwater harvesting systems.
A methodology for assessing irrigation system performance was developed by the then International Irrigation Management Institute (IIMI, now IWMI) in the 1990s in Burkina Faso. It was applied successfully to small-scale reservoir-based irrigation schemes (50-150 ha). The current study was carried out on two larger river-diversion irrigation systems in the south-west of the country, namely Vallée du Kou (1200 ha) and Karfiguéla (350 ha), in order to analyse and verify:• the applicability of the methodology to large-scale river-diversion schemes with more complex hydraulic networks and greater economic activities;• the relevance of the performance indicators used and the constraints pertaining to the acquisition of the basic data required for their determination;• the scope for adoption and application of the methodology by farmers' organizations for routine performance monitoring.The methodology seems well suited for large-scale irrigation systems, but its adoption by farmers' organizations has to be facilitated and accompanied by adequate training and the close involvement of the system managers. The indicators requiring the manipulation of a few physical elements can be determined relatively easily. Those involving water measurements are more difficult to calculate. The study makes a critical analysis of some indicators and demonstrates the evidence of the necessity to select among the indicators with regard to the irrigation system context.Ceux basés sur les quantités d'eau sont difficiles à obtenir. L'étude fait une analyse critique de certains indicateurs et met en évidence la nécessité d'adapter le choix des indicateurs au contexte du système irrigué.• the value of the production was calculated by multiplying the average paddy price per kilogram by the total block production; 308 Y. DEMBELE ET AL.
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