Estimation of Conveyance Losses of Wonji-Shoa Sugarcane Irrigation Scheme, Ethiopia

Abstract

To estimate the amount of conveyance losses through earthen canals and canal structures of Wonji-Shoa irrigation scheme, a study was conducted during irrigation season of 2010/2011. Current meter was used to collect discharge measurements from several locations and inflow-out flow technique was applied to estimate seepage and leakage losses. Seepages from fine textured or clay soils of selected primary, secondary, and tertiary canals while leakages from division structures, gates, broken canals and over flow on top of canals were determined. From the study, it was found that mean conveyance losses through seepage and leakages were 2,099.33 lit/day/m² or 12.36% and 48.82 lit/sec or 11.23%, respectively. Mean canal water velocity was 0.23 m/sec which is much below recommended value for fine textured soil. Even though seepage was related with discharge capacities of canals, it was aggravated by slow water velocity. Deformed and oversized canal conditions and poorly maintained water controlling structures were hampering smooth water flow of old aged canal networks of the scheme. To minimize the losses, rather than lining of selected canal by geomembrane, rehabilitating of the entire canal system is recommended as best option due to nature of canal system of Wonji Shoa irrigation scheme.

Keywords: conveyance, seepage, Wonji-Shoa, current-meter, Ethiopia