A breach in a flood defence will affect the downstream water levels in a riverine system, and therefore the flood risk of the system. The effect of this changed flood risk is used in an economical optimization to assess if this significantly changes the economically optimal safety targets of the flood defences in a riverine system. The impact of breaches on the flood risk and the economically optimal safety targets is modelled using simplified hydrodynamic relations and a number of conceptual case studies for small systems. Significant differences were found, but are limited to cases with a relatively high chance of breaching and/or high impact breaches. These differences seem to mostly affect the optimal heights of the flood defences, which means that including the effect of breaches can result in a different-optimal investment path.@en