Performance evaluation of Dakawa irrigation scheme Morogoro Tanzania

Abstract

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.