Tanzania Journal of Agricultural.Sciences. 2008 : 9 (1): 28 - 38
In Tanzania, irrigated land is less than 5% of the cultivated area much of which being
under traditional irrigation systems. Unfortunately, water in agriculture is indeed too often
misused and mismanaged due to lack of know-how of people and weakness of institutions.
This study therefore aimed at evaluating a simple approach for equitable distribution of
irrigation water using proportioning water division weirs with a view to improving system
performance in general. Five proportioning water division weirs were constructed along the
main canal to deliver water to eight branch canals of a typical farmer-managed irrigation
scheme. Flows to each of the branch canals were measured using calibrated staff gauges. The
discharge data along with climatic and crop data were used in the computation of various
irrigation performance indicators. Results showed productivity to be rather low, which was
attributed to low-level use of inputs including sub-optimal cropping intensities. The
relatively low values of output per unit irrigation supply suggest that the efficiency with
which water was being used in the scheme is rather low. Overall, equity of water supply (FE
= 0.14; AU = 0.52) appeared to be fair, which was an improvement over past experiences
before installation of the proportioning weirs. However, in spite of improvements in water
distribution, farmers still lacked basic understanding of irrigation scheduling which led to
some areas being over-irrigated while others faced water shortage.