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Many irrigation schemes which have been built in Tanzania are performing below
standard. This situation has resulted in low scheme production. Major causes for poor
performance may vary between different schemes. However, a comprehensive
performance evaluation of these schemes may bring a common understanding on the way
to improve the performance and enhance crop productivity in the irrigation schemes. This
Study was conducted to evaluate the overall irrigation performance of a cooperate
irrigation scheme in Dakawa Irrigation Schemes. In this scheme, water abstraction weir
was designed and constructed along Wami river to deliver water to a main canal in a
typical cooperate irrigation schemes. Flows to each of the secondary canals were
measured using calibrated staff gauges. The discharge data along with climatic data was
used in computing overall irrigation performance, irrigation water supply, distribution
performance, productivity of land and water, equity of irrigation water supply, relative
water supply, relative irrigation supply, water delivery capacity and irrigation ratio.
Moreover, social economic survey was also conducted to assess financial self-sufficiency,
fee collection, relative water costs, technical knowledge of staff and sustainability of
irrigable area. Irrigation performance indicators were also used to compare performance
among different cultivated areas. Review of documents, key informant interviews, focus
group discussions and field measurements was administered to collect information on
irrigation and land use practiced by farmers. The results show that the main canal supplied
4160 l/s of water for irrigation to all secondary canals which uses 4003 l/s during the
cropping season to meet crop demand for the entire irrigation scheme. However, the
farmers at the head and middle reaches abstracted more water than they required and
consequently caused a shortage of water supply to farmers at the tail-end reach. The result
also shows that the overall coefficient of variation in the discharge of water to al
secondary canals was within the acceptable range which is 67%. This adequate
coefficient of variation was due to improvements done in the whole scheme area including
the pump house. The seasonal equity of water distribution in secondary canals in Dakawa
was considered fair because all eight secondary canals equity values were above 62.5
percent. The productivity of land and output per command area in the Dakawa scheme is 8
198 346 US$. High productivity could be attributed to use of high–level inputs including
sub-optimal cropping intensities. The relatively high values of output per irrigation supply
suggest that the efficiency with which water is being used in the scheme is high. From the
focus group discussion, it was found out that farmers still have limited understanding of
irrigation scheduling and irrigation water management, as a result, some areas were overirrigated
while others faced water shortage. This situation calls for more farmers training
to be conducted in the Dakawa Irrigation Scheme. Same actions may be considered to
other existing irrigation schemes in Tanzania. |
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