Natural or unintended breaching can be catastrophic, causing loss of human lives and damage to infrastructures, buildings and natural habitats. Quantitative understand-ing of coastal barrier breaching is therefore of great importance to vulnerability as-sessment of protection works as well as to spatial planning against flooding hazards. The main objective of the present research is to develop a reliable process-based nu-merical model of coastal barrier breaching, which is capable of simulating both the breach initiation during storm surges and the barrier breaching due to overflow. The model is limited to homogeneous coastal sand barriers or similar types only, such as sand-dikes and sand dunes. The newly-developed model is referred to as a site model, i.e. the simulation domain is restricted to a representative cross-section of a barrier and the question where in plan a breach will occur is not answered by the model.