These challenges have been analysed in more depth in the OECD Guidelines for Cost-effective Agri-environmental Measures, with several recommendations that are sufficiently general to apply to the domain of flood risk mitigation (OECD, 2010b). Uncertainty in outcome is certainly undesirable for objectives such as bird conservation, but becomes socially unacceptable when it is about flood risks that can cause huge damages in cities, as well as injuries and loss of life. This may appear to give the advantage to structural measures which, despite their limitations and defaults, could offer more safety.