HEC-ResSim is selected as the reservoir simulation model. The main motivation of the study is to provide the necessary amount of water without excessively increasing the risk of downstream flooding. The study is divided into two basic operations; long term operation for daily water supply and short term operation for hourly flood protection. Three different approaches are tested using 2007 – 2011 data and the combined method is selected as the most suitable method for daily decisions.... Decisions for the effective management of water resources are getting more important due to continuously increasing population and water demand. Yuvac?k Dam Basin, located in the Marmara region of Turkey with 258 km2 drainage area, has high flood potential due to its steep topography, rainy climate and snowmelt contribution. Effective operation of Yuvac?k Dam Reservoir is a challenging task due to its relatively small reservoir capacity with 51.2 hm3 despite the annual need of 142 hm3 water demand.