Effects of climate change on stability of caisson breakwaters in different water depths Kyung-Duck Suh a,n , Seung-Woo Kim b , Soyeon Kim c , Sehyeon Cheon b a Department of Civil and Environmental Engineering & Engineering Research Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea b Department of Civil and Environmental Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea c Ocean Circulation and Climate Research Division, Korea Institute of Ocean Science & Technology, 787 Haean-ro, Sangnok-gu, Ansan-si, Gyeonggi-do 426-744, Republic of Korea article info Available online 19 March 2013 Keywords: Artificial neural network Caisson breakwater Climate change Sea-level rise Water depth Wave height abstract The effects of long-term sea-level rise and offshore wave-height increase due to climate change on the stability of caisson breakwaters constructed in different water depths are analyzed by using a time- dependent performance-based design method. An artificial neural network is combined with the wave transformation model to reduce the computation time in the Monte Carlo simulation. The breakwater is designed by the conventional safety-factor method, while its performance is evaluated by the expected sliding distance. In general, the stability of the breakwater is reduced if the climate change effects are included, but it shows different trends depending on water depth. Outside the surf zone, the effect of sea-level rise decreases with increasing water depth, whereas that of wave-height increase increases with water depth. Inside the surf zone, however, both effects decrease with decreasing water depth, with greater effect of wave-height increase than sea-level rise. In the design of a caisson breakwater of ordinary importance, it is not necessary to take into account the effect of sea-level rise, whereas the effect of wave-height increase should be taken into account if the breakwater is constructed far outside the surf zone. However, it should be noted that different results should be obtained if the breakwater were designed based on the expected sliding distance. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Recent rapid climate change is drawing the attention of coastal engineers to its effect on the stability of existing coastal struc- tures. It is also important to take its effect into account in the design of new structures. However, since the current design standards do not properly take into account the effects of climate change, it is difficult to cope with possible structural risks in the future. Moreover, since the current deterministic design method does not consider the uncertainties associated with the design variables, it cannot cope with future climate change which also involves great uncertainty. In addition, the current method which estimates the design variables based on the past environmental data is not suitable for taking into account the effect of rapidly changing coastal environment in the design of coastal structures of relatively long lifetime. Therefore, for properly taking into account the effects of climate change in the design of coastal structures, a probabilistic design method should be employed with accurately projected coastal environmental data for the future climate. During the past several decades, many studies have been conducted for the probabilistic design of vertical caisson break- waters. The papers presented in the books of Takayama (1994) and Kobayashi and Demirbilek (1995) describe the development of probabilistic design methods of vertical caisson breakwaters. Burcharth (1998) analyzed safety aspects mainly related to monolithic caisson structures, and presented a partial safety factor system for overall stability failure modes. Shimosako and Takahashi (2000) proposed the performance-based design method, which was improved later by including new concepts or design variables or by improving the calculation procedure (Goda and Takagi, 2000; Kim and Takayama, 2003; Hong et al., 2004; Esteban et al., 2007). Oumeraci et al. (2001) developed probabilistic design tools based on levels II and III reliability analyses and a partial safety factor system for vertical breakwaters. In this study, the performance-based design method is employed, in which the expected sliding distance (ESD) during the lifetime of the breakwater is calculated. There are several studies for the performance-based design method that can take into account the effects of climate change. Okayasu and Sakai Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/oceaneng Ocean Engineering 0029-8018/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.oceaneng.2013.02.017 n Corresponding author. Tel.: þ82 2 880 8760; fax: þ82 2 873 2684. E-mail address: kdsuh@snu.ac.kr (K.-D. Suh). Ocean Engineering 71 (2013) 103–112