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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., Hydraulic Structures and Flood Risk

In many parts of the world, flooding is a big risk. There are numerous strategies to reduce flood risk. The amount of flood risk reduction strategies grows exponentially with the amount of possible measures that can be implemented and possible timings when measures can be implemented. In this paper, the use of a financial method called “equivalent annual cost” (EAC) is assessed to reduce that number of strategies and evaluate cost-optimal strategies. The use of EAC allows the comparison between short-term and long-term measures by expressing them into an annual interest weighted expected expenditure. As soon as a measure has to be implemented (i.e. the annual risk becomes too large or the safety standards are exceeded), the EAC for all combinations of measures is determined and the combination is implemented with the lowest EAC. This almost leads to cost-optimal flood risk reduction strategies that, by manual optimization, can be improved further. A case study has also been performed in the Hollandsche IJssel which proved the use of EAC. Here it has led to cost-optimal flood risk reduction strategies. The method is tested in one case and it is recommended to apply and test it in other cases as well., Integral Design and Management, Hydraulic Structures and Flood Risk

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., Hydraulic Structures and Flood Risk

In many parts of the world, flooding is a big risk. There are numerous strategies to reduce flood risk. The amount of flood risk reduction strategies grows exponentially with the amount of possible measures that can be implemented and possible timings when measures can be implemented. In this paper, the use of a financial method called “equivalent annual cost” (EAC) is assessed to reduce that number of strategies and evaluate cost-optimal strategies. The use of EAC allows the comparison between short-term and long-term measures by expressing them into an annual interest weighted expected expenditure. As soon as a measure has to be implemented (i.e. the annual risk becomes too large or the safety standards are exceeded), the EAC for all combinations of measures is determined and the combination is implemented with the lowest EAC. This almost leads to cost-optimal flood risk reduction strategies that, by manual optimization, can be improved further. A case study has also been performed in the Hollandsche IJssel which proved the use of EAC. Here it has led to cost-optimal flood risk reduction strategies. The method is tested in one case and it is recommended to apply and test it in other cases as well., Integral Design & Management, Hydraulic Structures and Flood Risk