ali ebrahimzadeh - Ph.D. Candidate, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
mahdi zarghami - Professor, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
vahid nourani - Professor, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Risk assessment ofthe hydraulic structures is one of the serious concerns of researchers especially in earth dams. Using uncertainty and risk analysis, it is possible to use uncertain parameters in mathematical equations for designing. This paper considers the different uncertainties related to flood and wind with various return periods and uses system dynamics to evaluate overtopping risk on earth dams in order to mitigate this risk and then increase the earth darn s operational Iife. In order to evaluate risk in proposed model, we use Monte-Carlo simulation (MCS) method with different iterations. In this research, system dynamics is used as a simulation OF overtopping risk in the Hajilarchay dam, Northwestem Iran. The results show the effectiveness of system dynamics in earth dams overtopping risk assessment with different parameters effecting the overtopping risk. Moreover, opening the bottom outlet of the Hajilarchay dam could cause 12 percent reduction in overtopping risk. Also overtopping risk obtained from the Monte- Carlo simulation is one to two percent greater than Latin hypercube sampling and with less simulation running time. It can be concluded that system dynamic is very effective tool for evaluation and calculation of overtopping risk of dams and is easier and faster than other common numerical methods like Programming

Earth dam, Overtopping risk, System dynamics, Uncertainty, Return period