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 water delivery performance of the physical structures in Allawuha irrigation scheme was not clearly understood so far; 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 assessing irrigation water supply versus demand and using 10 internal process indicators classified under water delivery and maintenance indicators. As per the results, deficit in supply was observed during April and May, which was 35.16 and 25.53% respectively. However, supply was exceeding the demand by 60.47% during March. The highest spatial deficit was observed at the last outlet point and the lowest at the first outlet point. The overall water delivery performance of the canal in relation to adequacy, dependability, equity and efficiency were found to be 0.56, 0.47, 0.22 and 0.96 respectively. Therefore, water delivery performance of the canals was poor in terms of adequacy and dependability; however it was good and fair for efficiency and equity respectively. Similarly, delivery performance ratio and equity ratio for head to tail were found to be 0.74 and 2.73 respectively. These values indicate, the existing performance of the main canal was declined as compared with the intended and also management of delivery was poor from head to tail reach of the system. Maintenance indicators like water surface elevations ratio, effectiveness of infrastructure and sustainability of irrigated area were found to be 78%, 28.13% 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 become nonfunctional. Based on the results from this study non-proportionality of irrigation water demand with supply, poor water delivery system, absence of frequent maintenance, and the management aspects were problems strongly affecting the hydraulic performance of the scheme. Therefore, it is suggested that, frequent maintenance, optimal crop plan, and apply a strong water delivery plan are required to mitigate these problems.