ali komak panah - Associate Professor, faculty of civil and environmental engineering, Tarbiat Modares University, Tehran, Iran
Hamidreza rahmani - Phd candidate, faculty of civil and environmental engineering, Tarbiat Modares University,Tehran, Iran

In hydraulic structures which are located in a natu.ra.l environment, there is the possibility of system failure with increasing external forces acting on the structures. Stability and crest settlement of rockfill dams is a major factor in design which in some cases is very important (after construction and impoundment). Particle breakage in rockfill dams is the main cause of vertical deformations. Particle breakage changes resistance and deformation behavior of rockfill materials and this affects the performance of dams. Forembankment dams the highest risk of damage is caused by water overtopping over the dams. The purpose of this research is to study rockfrll dams settlement and Eeeboard height reduction that affect performance of dams, especially during the heavy flooding. Increasing in the probability of dams overtopping results in total destruction of the dam. In this research the overtopping risk analysis method has been studied and the effective parameters on overtopping risk analysis and the effect of particle breakage on overtopping risk of rockfill dams was investigated

particle breakage, rockf 1ll dams, overtopping risk, Mahabad dam