Water in the life of human beings is like a two sided medallion. In one side of the medallion the demand for water lies which includes domestic, industrial, agricultural and recreational use of water resources. The better these demands are satisfied, the better a life on earth will a human being has. The problem about the first side of the medallion is that water is not always available in the desired quantity (e.g. droughts) and quality (e.g. pollutants). In the other side of the medallion, the undesired abundance of water (floods) lies. The problem about the second side of the medallion is that when water is uncontrollably abundant especially for short time periods, it causes loss of human lives and great damage to properties. Turkey, which is one of the most populated countries in Europe, deeply faces the two problems defined above. Cities like Izmit are rapidly growing and water demand and disastrous effects of abundant water in these cities are increasing. This study intends to apply a hydrologic model to Yuvacik Basin which shall be used as a decision support tool for the operation and maintenance of Yuvacik Dam.