The research team, led by Getachew Bereta Geremew and Lemita Berisha Urto of the Arba Minch Water Technology Institute at Arba Minch University, together with Aklilu Debissa Gidebo of the Wolaita Town Irrigation Development and Drainage Service Office, set out to answer a deceptively simple question: how well is the Lasho scheme actually performing, decades after it was commissioned? Rather than relying on farmers’ impressions or administrative records alone, the investigators applied a standard diagnostic framework built around three families of indicators: hydraulic performance, physical sustainability, and maintenance condition. Each family captures a different dimension of system health, and together they reveal whether a scheme is failing because of physics, management, or both.

Hydraulic performance indicators describe how faithfully a canal network delivers water in the amounts, at the times, and to the locations that crops require. The team measured discharge directly at three points along the main canal, at the head, middle, and tail reaches, using a 90-degree V-notch weir, a sharp-crested triangular structure whose stage-discharge relationship allows flow rate to be computed from a single water-level reading. They also recorded water surface elevations at 36 stations along the canal, comparing current levels against design levels to detect sediment buildup and channel roughness. Secondary data on climate, crops, and design specifications came from national government offices and were processed with CROPWAT 8.0, ArcGIS 10.3, and New_LocClim 10.1 software to establish how much water the scheme should have been delivering under local conditions.

The hydraulic results were sobering. Adequacy, a measure of whether delivered water matches crop water requirements, scored 0.79, below the 0.90 threshold generally considered good. Dependability, which reflects how consistently water arrives at the right time, scored just 0.202, far below the 0.80 benchmark for reliable delivery. Equity, which captures how fairly water is shared between head-end and tail-end users, scored 0.253, indicating that farmers at the downstream end receive dramatically less water than those near the intake. Efficiency, the ratio of water beneficially consumed to water delivered, was the only indicator to reach fair territory, at 0.70. The scheme as a whole experienced a 15 percent water deficiency, but the deficit was not evenly distributed: the tail reach suffered an 18.8 percent shortfall, the worst of any section.

Physical sustainability indicators tell a parallel story about the scheme’s capacity to keep serving its intended area. The team found that only 48 percent of the irrigable command area is currently being irrigated, meaning more than half of the land the canal was designed to water receives nothing from the system. The sustainability of the irrigated area itself stands at 60 percent, a figure that reflects both shrinking coverage and the gradual loss of infrastructure that once supported it. In practical terms, the scheme is operating at roughly half of its designed agricultural capacity, a gap that translates directly into lost harvests for a region where small-scale irrigation is a cornerstone of food security and poverty alleviation.

Maintenance indicators, the third diagnostic family, explain why the hydraulic and physical numbers have drifted so far from design intent. The water surface elevation ratio, computed by comparing current water levels at 36 stations against design elevations, came in at 0.72, a value that signals significant sedimentation and weed growth within the canal. When sediment accumulates on the canal bed, the water surface rises relative to the design level for any given discharge, reducing effective conveyance capacity and forcing operators to ration flow. Compounding this, only 62.22 percent of the scheme’s irrigation structures remained functional at the time of the survey, meaning nearly four in ten gates, drops, division boxes, or related components were broken, silted, or otherwise out of service.

The delivery performance ratio, a key water delivery indicator, scored 0.8, confirming that the main canal achieves only 80 percent of its design discharge. This single number ties together several failure modes: sedimentation has reduced the canal’s cross-sectional capacity, weed growth has increased hydraulic roughness, and structural decay has likely introduced leaks and obstructions along the route. The result is a network that cannot physically move the volume of water its designers intended, even when supply at the source is adequate. Because the deficit is worst at the tail reach, the scheme’s most distant farmers bear a disproportionate share of the burden, a pattern that erodes trust in water-sharing arrangements and can trigger conflict among users.

The authors attribute the scheme’s poor performance across most hydraulic indicators to a combination of technical problems, managerial issues, and operational constraints, rather than to any single cause. Technical failures include sediment accumulation, weed invasion, and the deterioration of control structures. Managerial weaknesses likely include inadequate maintenance scheduling and insufficient oversight of water allocation. Operational constraints may involve the capacity and incentives of water user associations, the community institutions responsible for day-to-day water distribution. This tripartite diagnosis matters because it implies that no single intervention, whether dredging the canal or repairing a gate, will restore full performance on its own; the system requires coordinated action across engineering, governance, and farmer engagement simultaneously.

The study’s conclusions point toward a specific set of urgent interventions: routine maintenance to clear sediment and weeds, structural rehabilitation to restore the roughly 38 percent of nonfunctional components, improved water management to raise dependability and equity, and stronger water user associations to enforce fair distribution and sustain upkeep over time. The authors also call for future research to prioritize long-term monitoring across multiple seasons, along with socio-economic and cost-effectiveness analyses of rehabilitation options, recognizing that a single-season snapshot cannot capture the full variability of rainfall, crop demand, and institutional capacity that shapes scheme performance year after year.

For the broader community of irrigation engineers, water managers, and policymakers, the Lasho case offers a methodological template as much as a warning. The combination of direct discharge measurement with a V-notch weir, systematic water surface elevation surveys at dozens of stations, and crop-water modeling with CROPWAT provides a replicable diagnostic toolkit that can be applied to thousands of similar schemes across Ethiopia and beyond. As climate variability intensifies pressure on water resources and food production, the ability to quantify exactly where and why an irrigation system is underperforming, rather than merely observing that crops are thirsty, becomes an essential step toward targeting scarce rehabilitation funds where they will do the most good. The Lasho scheme’s numbers, 0.79 adequacy, 0.202 dependability, 0.253 equity, 0.70 efficiency, 0.8 delivery performance, 0.72 water surface elevation ratio, and 62.22 percent structural functionality, now stand as a concrete baseline against which future repairs and reforms can be measured.

Subject of Research: Hydraulic performance and sustainability evaluation of the Lasho small-scale irrigation scheme in Wolaita Zone, Ethiopia

Article Title: Evaluation of hydraulic performance, physical sustainability and maintenance indicators of the Lasho small scale irrigation scheme in Wolaita Zone, Ethiopia

Article References: Geremew, G. B., Gidebo, A. D., & Urto, L. B. (2026). Evaluation of hydraulic performance, physical sustainability and maintenance indicators of the Lasho small scale irrigation scheme in Wolaita Zone, Ethiopia. Discover Sustainability. https://doi.org/10.1007/s43621-026-05028-1

Image Credits: AI Generated

DOI: 10.1007/s43621-026-05028-1

Keywords: irrigation, Ethiopia, hydraulic performance, water scarcity, sedimentation, water user associations, CROPWAT, sustainability, canal, food security, Evaluation, hydraulic