This study was conducted to evaluate the performance of two small-scale irrigation (SSI) schemes in the sub-humid Ethiopian highlands. Water application at the farm level was monitored using partial flume and the average flow velocity along the main canal was measured using the current meter. The infiltration measurement was conducted at the head, middle, and tail of the scheme within the command area using a double-ring infiltrometer. Soil samples were collected using an auger up to 60cm depth. Climatic and agronomic data were collected from the nearby meteorological station and woreda agricultural office, respectively. CROPWAT was used to determine the water requirement of crops.
The result showed that the average conveyance efficiency for the lined main canal was 90% and 92% for Mugie and Fesas SSI, respectively. The conveyance efficiency for the unlined main canal was in the order of 86% and 87% for Mugie and Fesas SSI. On the other hand, the average application efficiency and overall efficiency were found to be 56% and 51%, respectively, with storage efficiency of 50% for Mugie irrigation scheme. Similarly, the overall, application and storage efficiencies were found 50%, 54%, and 56%, respectively, for Fesas irrigation scheme. The relative irrigation and water supplies were 1.23 and 3.17, respectively, for Mugie SSI, while the supplies were 0.94 and 2.45, respectively, for Fesas SSI.
Conveyance efficiency for both Mugie and Fesas schemes was found below standard (95%) and overall efficacy was low as well (~50%). Failure of operating gates in the main canal, overtopping of water from the main canal due to canal siltation, and leakage through the main canals were the main causes for poor performance. Improvement measures are needed for both Mugie and Fesas irrigation schemes and institutional support is vital to improve and maintain the failure of infrastructures for better performance.