The exploitation of the structures (planes, engines) and of the infrastructures (dams, nuclear thermal power stations) with a very high cost of realization and a significant working life must be done with a risk of damages and failures reduced and controlled. This paper proposes a case study for the risk assessment of a hydraulic structure under random contingencies effects by using reliability and vulnerability measures. The reliability which can be defined as the probability that the system will remain in a non-failure state, and vulnerability which represents the system's susceptibility to failure have been investigated in this paper. Our study provides a helpful approach for an effective utilization and combination of reliability and vulnerability indices to improve the functioning and security, and to take an adequate decision on the system state.