All plant components that assume safety functions to meet the safety goals as described in Section 2.5 must be protected in such a way that they continue to perform their safety

functions even in the event of extreme floods. This calls for a specific plant protection strategy which requires flood protection measures including structural protection measures.

Structural protection measures with their flood protection structures must in principle provide permanent flood protection against design water levels. Alternatively, tempo­rary flood protection measures may be included in the safety strategy if there is sufficient advance warning time. KTA 2207 [23] defines the design water level as the highest water level that can be expected with a probability in excess of 10~4p. a., in front of the protective structure or plant component to be protected.

The main protective measures, especially in coastal areas, include dykes enclosing plant components to be protected against floods. These can be divided into inland and sea dykes, depending on the differing design water levels involved with inland and coastal locations (see also Section 5.3).

Sea dykes are particularly important, as the flood risks involved may be assumed to be relatively high (Figure 4.7) (cf. [24]). For the governing storm flood water level, which consists of the storm flood water level plus wave impact, dykes must be designed to demonstrate a sufficient dyke height, allowing for possible minor wave overflows, and sufficient stability. These proofs are influenced significantly by dyke structure (mate­rial) and cross-section with its internal and external slope angle (geometry).

As well as dyke design verification proofs, there must also be a monitoring programme to review settlements at regular intervals, for example annually, which must be assumed as the settlement forecasts with the proofs. If settlements exceed permitted levels, repairs must be made, and as the storm flood risks are greater in autumn and winter, these can only be carried out during the summer months.