1 PROBABILISTIC DESIGN AND RELIABILITY ANALYSIS OF COASTAL STRUCTURES-A VIETNAM CASE CONG- MAI VAN Water Resources University of Vietnam; 175 Tay Son, Dong Da, Hanoi, Vietnam & Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands HUNG- NGUYEN QUANG Water Resources University of Vietnam; 175 Tay Son, Dong Da, Hanoi, Vietnam HAN VRIJLING & PIETER VAN GELDER Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands In this paper the reliability analysis of sea flood defence systems and the probabilistic approach of the design of the sea flood defences are outlined. The application of probabilistic design methods offers the designer a way to unify the design of engineering structures, processes and management systems. For this reason there is a growing interest in the use of these methods in the design and safety analysis of civil engineering system including coastal flood defences. In this paper these methods are critical reviewed. The so-call probabilistic safety assessment and reliability based design models are developed and applied to a coastal flood defence system in Nam Dinh, Vietnam. An accurate safety assessment of the existing coastal defence system and a set of reliability based solution are, therefore, of large importance for rehabilitating coastal flood defences of the considered case study area. In accordance with present situation and analysis results, the coastal flood defences in Nam Dinh is not strong enough to withstand the actual sea boundary condition and ensure the safety for protected areas in views of present socio-economic development. As part of knowledge transfers, the analysis results could contribute to fundamental base for long-term planning rehabilitation of the sea defences in Vietnam. 1. Introduction Use of probabilistic design methods is increasing in civil engineering design in general and hydraulic/coastal engineering in particular. In order to undertake an effective design and assessment of the overall reliability of a coastal structure it is essential to have a thorough knowledge and understanding of all possible failure modes in the design stage. Last few decades effort has been devoted to improving our knowledge of how the structure system fails and the probabilistic design concepts have been increasingly proposed and applied to the field of hydraulic/coastal engineering (see e.g. the concept, method and application in Bakker & Vrijling 1980; Vrijling et al. (1998); Voortman (2002); and Oumeraci et al. (2001)). However, gaps in knowledge still remain in widening applications of the probabilistic approach in design and safety assessment of coastal structures i.e. estimating the appropriate statistical distributions of the sea loads acting on the structures; investigating the appropriate characterization of failure mechanisms of coastal structures; description of the structure system as a whole and