Performance Analysis of the Doho Rice Irrigation Scheme in Uganda

Abstract

The study analyzed the performance of Doho Rice Irrigation Scheme (DRIS), the largest public irrigation scheme in Uganda, using (1) water supply indicators comprising relative water supply (RWS), relative irrigation supply (RIS), and water delivery capacity (WDC) related to water supply from the system in relation to scheme crop water demand for the 2018–2019 growing season; and (2) water balance ratios of conveyance, distribution, application, and storage related to water utilization efficiency during the same period. Primary field data were collected in 2021 through measurements of canal water flows at different system levels, and measurement of field level soil properties and moisture contents. Climate data from Uganda National Meteorological Authority, Tororo station, were analyzed using commercially available software to compute the crop water and irrigation requirements of paddy rice. From the analyses of the water supply indicators, the result of the ratios of RWS, RIS, and WDC were, respectively, 2.82, 9.04, and 2.28, whereas conveyance, distribution, field application, and storage efficiencies were, respectively, 80.7%, 78.4%, 71.6%, and 87.5%, with an overall scheme efficiency of 57.8%. RWS and RIS values higher than one mean DRIS has plenteous water supply, sufficient to meet crop water demand. In particular, a RWS value of 2.82 shows adequate supply relative to demand. The RIS value of 9.04, significantly higher than the ideal value of one, suggests notable inefficiencies in water usage within the DRIS. Also, the WDC value of 2.28 shows that the canal capacity was not a limiting factor to meeting the peak consumptive requirement. Despite this plenteous supply, analysis of efficiency shows that the water was not particularly efficiently distributed nor efficiently applied, even though the storage efficiency was high. Methodological lessons from the study emphasize more data collection intensity and more adequate data treatment to gain more comprehensive insights into irrigation system performance.