HYDRAULIC PERFORMANCE EVALUATION OF SMALL SCALE IRRIGATION SCHEME; CASE STUDY OF ALLAWUHA IRRIGATION SCHEME, NORTH WOLLO, ETHIOPIA

Abstract

Performance assessment in irrigation systems plays a vital role in identifying the gaps and applying mitigation measures. The possible benefits of the Allawuha irrigation scheme is scarcely understood, hence the objective of the study was evaluating the hydraulic performance of Allawuha small scale irrigation scheme. This study was carried out for a single irrigation season from February to June, 2016. Hydraulic performance of the scheme was evaluated by comparing irrigation water demand with actual supply, and using 10 internal process indicators classified under water delivery, utility of water supply and maintenance indicators. As per the result, deficit of supply has been advanced in April and May; hence actual irrigation water supply was 35.16 % in April and 25.53 in May more than the demand. However, supply was exceeding the demand by 60.47% during March. On average, irrigation water supply was observed in shortage of the requirement at the outlet point one, three and five, whereas in excess of the requirement at the outlet point two and four. The overall water delivery performance indicators; adequacy, dependability, equity and efficiency were found to be 0.56, 0.47, 0.0.22 and 0.96 respectively. According to these values, performance of water delivery canals was rated as poor in terms of adequacy and dependability; however it was good and fair in relation to efficiency and equity respectively. Utility of water supply indicators; deficiency, delivery performance ratio and equity ratio for head to tail were found to be 0.30, 0.63, and 2.73 respectively. These values indicate that, the performance of the main canal was declining from the intended and distribution of water between the head and tail was unfair. Maintenance indicators; water surface elevations ratio, effectiveness of infrastructure and sustainability of irrigated area were found to be 78%, 26.09% and 97.8% respectively. These values indicate that, actual water level as well as command area was reduced from initially designed, and a number of structures initially installed were becoming nonfunctional, then maintenance of the system is necessary. The results from this study are very clear to that of, non-proportionality of irrigation water demand with supply, poor temporal water delivery system, absence of frequent maintenance, and management aspects have been strongly affected the hydraulic performance of the schemes. Therefore, it is suggested that, frequent maintenance, optimal crop plan, and apply a strong water delivery plan are required to mitigate these problems