Evaluation of hydraulic and hydrologic factors influencing irrigation water use efficiency in the Gomit irrigation scheme, South Gondar, Ethiopia

Abstract

Hydrological and hydraulic factors are critical for controlling irrigation water use efficiency, which have influenced water availability, distribution, application, and crop productivity in irrigation projects. This study aimed to assess how hydrologic and hydraulic factors affect the efficiency of the irrigation water use in Ethiopia’s Gomit Irrigation project. To diagnose system inefficiencies, a mixed-methods approach was employed, combining inflow records, reservoir storage, canal hydraulic parameter measurements, soil water dynamics analysis, and crop water requirements. Aqua Crop model, empirical analyses, and statistical analyses were used as the data analysis tools. Hydraulic efficiency was computed as the ratio of water diverted into the canal to water delivered at the canal outlet. The finding revealed significant loss across soil and canal systems. The annual irrigation requirement value of 406.1 mm and infiltration from rainfall (10.6 mm) were offset by drainage loss (48.3 mm). The high evapotranspiration value of 593 mm created the net irrigation demand, highlighting the need for accurate water scheduling. The soil moisture level varies from 20 to 21.7% underscoring the importance of continuous monitoring to reduce crop stress. The performance of the canal was less than the design capacity, constrained by discharge (0.27 vs 4.275 m3/sec, hydraulic efficiency (0.4), and conveyance (74%) due to roughness, evaporation, and seepage. The inefficiencies have reduced the irrigated land by 1.4 ha (0.59 ha and 0.79 ha, respectively, due to seepage and evaporation), with peak losses occurring during the critical crop growth months. Furthermore, the reliability of the reservoir (75%) was restricted by the seasonal inflow variability, making water deficits of 2.22 m3/sec and 2.03 m3/sec in February and March, respectively. The salinity risk (0.45 dS/m) is an extra limiting factor for which improved drainage, along with salt-tolerant crops, should be considered. The result highlights the necessity for integrated management solutions. To evaluate irrigation system performance, water use efficiency has become a central concern, with metrics such as crop water productivity, conveyance efficiency, and net irrigation demand widely used to assess system performance.