In the previous chapter we looked at the historical use of flood defenses for defensive purposes. Adversaries on the other hand will want to break through these defenses. In this chapter we will research events in the more recent history of the Second World War. Offensive actions during Second World War show that there can be many reasons for attacking flood defenses like levees and dams. These Second World War attacks give us an impression of the vulnerability of flood defenses, and the forces needed to breach them. This in turn tells us something about the effectiveness of offensive weapons in relation to flood defenses. It may also give us an indication of possible protective measures such as strengthening or defensive redesign.
In the previous chapters we discussed various flood defense and flood barrier constructions, following a historic footpath according to the year that the barrier was completed and became operational. This approach helped us to step-by- step broaden our insight in the technological progress in flood barrier construction. At the same time, we started developing our flood defense vulnerability and attack-type tables for various types of flood barrier. In order to be able to look at these vulnerabilities form a wider perspective, we looked at the use of water for defensive purposes, and the effects of flood defenses under attack. This approach helped us to better understand the safety risks and security threats associated with flood defenses and flood barriers.
In the previous chapters we looked at flood defenses from different perspectives. In our historic overview we saw flood defense systems growing both in size and technical complexity. The most recent development however is that flood barriers tend to get smaller and simpler in design (but with advanced technology being used). We assume that both size and complexity increase the chance of safety risks. We gave an overview of such safety risks in several flood defense vulnerability tables. Structural weaknesses in, and vulnerabilities of, flood defenses may be exploited by possible attackers. By adding such security risks to our vulnerability tables, and then assessing the impact of specific attack types to vulnerable parts of the flood defense, the (safety-related) vulnerability tables become (security-related) attack vulnerability tables. In this chapter we will further discuss the concept of (security) risk, cascading (security) risks and how the occurrence of a security threat and the connection with effects and consequences can be presented in a bowtie diagram. We also introduce new risk variables that transform our attack vulnerability tables into attack-type tables that help us draft a complete attack scenario and calculate the probability and effectiveness of various attack types. With this approach we hope to link thorough vulnerability analyses with security risk analyses that can be effectively used in security practice.