Risk Awareness – Key to a Sustainable Design Approach for Breakwater Armouring
Summary
In prosperous periods people tend to overestimate their capabilities and to accept significant risks. This is a widespread tendency, which led to the financial crisis in 2008. It can be seen back also in the variation in time of investments for flood protection schemes and affects last but not least the designing of breakwaters. A number of major breakwater damages occurred in the late 1970th and early 1980th (a.o. Sines, 1978; Arzew, 1980; Tripoli, 1981). In the period thereafter designers applied larger safety margins. However after more than 25 years without any spectacular failure of a major breakwater; often we see that many of the intuitively applied safety margins are disappearing. This tendency is supported by the new role of consulting engineers in EPC contracts and PPP's. Designers are working more closely with contractors; there is more focus on efficiency. This results in breakwater designs that are close to or right on the edge.
An important aspect in the design of breakwater armour is the determination of the design wave height. Commonly return periods of 50 or 100 years are used, although the lifetime of breakwaters may exceed 100 years. Despite the fact that a design wave height is used which may be exceeded several times during the lifetime of the structure, no safety factors are applied. This is in contrast to the safety factor approach of structural engineering. As a consequence, severe damage may occur if design wave heights are exceeded or if the effect of important design aspects has been underestimated or not considered.
The paper will address relevant design aspects that are not sufficiently covered by present design methodologies and their possible effect on the armour layer stability. Guidance will be provided on how these aspects should be considered in the armour layer design.