Abstract : Despite considerable scientific progress in the field of Design, Construction, Operation and Maintenance of dams using safe and secure methods, nonetheless the study of dam breakings is still on the agenda of managers and experts of the field .In fact study of dams breaking in some countries are inseparable parts of the safety of dams. Perhaps the most important reason for these studies is the great danger associated with the breaking of dams and assessing the related dangers, to say the least. Floods resulting from breaking of dams are the most disastrous events in the last two centuries.In this kind of flood, considerable volume of water in a short period of time runs at the downstream and makes great waves at the end of the river and since most rivers don't have the capacity needed to pass the flood safely, the wave of the flood will eventually divert from the main rout and threatens the cities, villages and facilities on the way. In general the purpose of dam breaking studies is to complete a chain of safety measures concerning dams. In fact these studies are the last link to this chain.And in this case the main purpose of this research is numerical simulation resulting from breaking of Yamchi dam and its most important end result is mapping out the flooded area and detecting some important specifications of the flood water such as Depth, Speed, Time of reaching the flood to the designated points, Residing and Receding time of the flood in the flooded area. In other words the main goal of this research is to develop a quantity based effect of dam breaking to assess the probability of dangers facing important facilities at the base of dams and assessing the risks involved in order to prioritize an emergency action plan of Operation, Maintenance and Research activities.Yamchi soil dam is located at the upper city area of Ardabil on Balkhloochay River. After investigating the history of Dam breaking worldwide especially soil dams, two mechanisms of overtapping and piping was considered for Yamchi soil dam. In these studies different scenarios of Yamchi dam breaking is simulated and the results were evaluated.The evaluted scenarios in these studies are as follows:
1. Breaking of Yamchi dam in a flooding day at the maximum possible strength of the flood (Overtapping).
2. Probable dam breaking in a sunny day with the mechanism of Piping.
3. Probable dam breaking at the time of flooding with return period of 10000 years at the location of dam (overtapping).
The result of Simulation indicates that of three scenarios probable in the case of Yumchi Dam breaking (Overtapping, Piping in a sunny day, and 10000 years return flooding), The scenario of overtapping is the worst scenario for breaking of Yamchi dam and would cause the break of Almas diversion dam as well.