Water resources of the dry Haramaya Lake Basin have been used for agriculture and water supply purposes in unsustainable manner. Since the disappearance of the lake, agricultural area has expanded to the dry lake and farmers started to irregularly pump water out of the basin ground water. This coupled with the inefficient irrigation has caused further pressure on the depleting water resource of the basin. Hence, this study was carried out to review and evaluate the existing irrigation water management practices and develop alternative intervention for optimum irrigation water withdrawal from the Lake basin. Field measurements, interviews and focal group discussion were made to collect primary and secondary data related to soil, crop, metrological, and irrigation parameters. The irrigation water withdrawal under the existing condition was estimated considering the pumping rate, irrigation duration and interval and area irrigated. In addition, CROPWAT software was used to determine the water requirement of crops for ET (evapotranspiration) based irrigation system. For all crops, the applied irrigation water under the traditional irrigation was well above the recommended rate. A reduction in applied irrigation depth of 60% (minimum) and 79% (maximum) was obtained by shifting from the traditional irrigation system into the ET based irrigation system. The water productivity was increased by 230% for carrot and by 75% for tomato in the ET based irrigation system as compared to the traditional irrigation system. Similarly, with the ET based irrigation system, the average water withdrawal per hectare of land was decreased by 56% (from 9336 to 4051.4 m-3.ha). This study, therefore, urges for immediate intervention in replacing the existing traditional system to the ET based irrigation system.
Key Word: CROPWAT, Over irrigation, Traditional water productivity, Water withdrawal