The Ethiopian government is involved in the development of massive irrigation projects forrnsugar production in different parts of the country. One of these schemes is the Wolkayiternsugar development project, located in the western zone of the Tigray region. It is planned tornutilize the runoff of the Zarema River, which is a major tributary of the Tekeze river basin.rnTo achieve this objective, a dam has been built across river Zarema, which would enablernirrigation of more than 40,000 ha of land. The Sugar cane which is estimated to be cultivatedrnaround 40,000 ha of land is to be utilized as raw material for Welkit sugar factory which hasrna capacity of 24,000 TCD.rnThe objective of the study is to develop operation modeling for the Zarema May Day Damrnreservoir. The input data consider for the model are daily inflow, monthly irrigation, andrnmonthly reservoir surface evaporation, and Zarema May Day Dam physical data.rnThe reservoir operation modeling was done using Zarema river inflow source options. Thernhigh Simien mountain range ensures relatively high runoff in the river Zarema at the damrnsit. The annual average runoff is around 1300Mm3.rnThe seasonal flow regime is characterized by an important average monthly flow,rnparticularly in July (169 m3/s) and August (225 m3/s), whereas the period from October tornMay exhibits a monthly average lower than the annual mean.rnThe reservoir operation modeling has been developed using two cases of inflow and threerndifferent scenarios, which has the same operation zone but differ irrigation area in Ha. Andrnalso reservoir operation guide curve and each year reservoir pool level were established.