Economically optimal safety targets for interdependent flood defences in a graph-based approach with an efficient evaluation of expected annual damage estimates

Abstract

Abstract. Flood defence systems can be seen as multiple interdependent flood defences. This paper advances an approach for finding an optimal configuration for flood defence systems based on an economic cost-benefit analysis with an arbitrary number of interdependent flood defences. The proposed approach is based on a graph algorithm and is, thanks to some beneficial properties of the application, able to represent large graphs with strongly reduced memory requirements. Furthermore, computational efficiency is achieved by delaying cost calculations until they are actually needed by the graph algorithm. This significantly reduces the required number of computationally expensive flood risk calculations. In this paper, we conduct a number of case studies to compare the optimal paths found by the proposed approach with the results of competing methods that generate identical results. The proposed approach is set up in a generic way and implements the shortest-path approach for optimising cost-benefit analyses of interdependent flood defences with computationally expensive flood risk calculations.

Impact of including interdependencies between multiple riverine flood defences on the economically optimal flood safety levels

“…A recent numerical method that is capable of optimising flood defence systems with multiple interdependent defences can be found in [14] and [21]. The study in [13] uses a similar approach as in [14] to optimise flood defence systems with multiple interdependent defences, but attempts to reduce the number of EAD calculations required by the numerical optimisation method.…”

“…Even if the system configuration does not change, the EAD can change due to temporal changes (see also Section 3.3 & 3.4). Using the numerical optimisation method of [13], the number of EAD calculations is reduced by only executing the calculation of the necessary estimates which are used by the optimisation routine (i.e. 'lazy evaluation').…”

“…A series of investments are needed to make sure that the defence remains at an optimal level from an economic point of view due to (over time) changing expected annual damages. Image reproduced from [13].…”

“…The work presented here builds upon previous work done in [15,16,13]. The general idea of performing an economic optimisation with EAD estimates based on hydrodynamic interactions between flood defences was also used [15], but with less types of hydrodynamic interactions and applied to a (different, simpler) coastal system.…”

“…[16] discusses some fundamental impacts of including riverine hydrodynamic interactions on an economic optimisation, but does this using an analytical economic optimisation and hypothetical, small riverine systems. The economic optimisation method discussed in [13] is applied here as part of the case study.…”