CONVEYANCE AND WATER USE EFFICIENCY IN THIRTY YEARS OLD IRRIGATION SCHEME: ESTABLISHING BASELINE INFORMATION TO REVITALIZE THE MEKI-ZIWAY IRRIGATION SCHEME

Abstract

Meki-Ziway Irrigation Scheme is a pumped-gravity irrigation scheme established in 1986. The scheme is currently characterized by poor on-farm and off-farm irrigation water management. Irrigation performance assessment has not been carried out for Meki-Ziway irrigation scheme in Ethiopia since its operation. In this study, the conveyance system and irrigation practice was evaluated at field level. The main pump discharge was measured in two ways, (i) by measuring the duration which is required to fill the stilling basin: (ii) using current meter to measure the velocity of the water. The conveyance efficiency of the main canal was determined by estimating discharge at three reaches. On farm field application was evaluated in four farm plots with three replicas in each plot. Furrow inflow rate, cutoff time and soil moisture content in the root zone of crops was monitored. Inflow rate was measured using bucket method while soil moisture content before and after irrigation application was measured by using a portable soil moisture sensor. The soil moisture also monitored at daily time intervals over a period of 25 days. The instrument was calibrated by laboratory result. The monitoring was conducted in two periods: in a time when there was a better water availability and in a time when there was water scarcity. The extent, need and effect of new water users were investigated through household survey and necessary data measurement. These new users were not a part of the scheme originally. The result shows that the main pump is being operated at a mean discharge of 512.046 l/s. the mean conveyance efficiency of the main canal is 43.83% while the efficiency of the secondary canal is 89.72%. Many of the secondary and tertiary canals are poorly maintained and many of the structures are dysfunctional. The study result also shows that only 45.44% to 74.24% (mean value 58.06%) of the applied irrigation water amount is stored in the crop root zone while the remaining is lost by deep percolation and runoff. The result varies across farm plots, replicas and irrigation event. Analysis of the continuous soil moisture records indicates that amount of water stored in the rote zone varies with the location of the farm plots. Farm plots at the canal head, which have good access to water, were mostly irrigated up to the soil saturation level and their moisture level hardly drops below the permanent wilting point. For farm plots which are located far from the canal head, the soil moisture content drops below the permanent wilting point for a number of consecutive days due to limited access to irrigation water. There is no appropriate water allocation system in the scheme that would ensure equity across the reaches. Overall, there is a strong need to rehabilitate the physical infrastructure of the scheme by considering the new users and enhance farmer’s knowledge of crop yield response to water application. Future interventions should provide incentives to farmers to improve the current irrigation efficiency levels. There should introduce appropriate water allocation system in the scheme that would ensure equity across the reaches