Risk assessment of some revetments in Southwest Wales, United Kingdom

The new risk assessment model in which the second-order reliability method and the importance sampling Monte Carlo (ISMC) simulations were interrelated was implemented to Wiseman's Bridge, Newport, and Broadhaven revetments in the Pembrokeshire Coast National Park, southwest Wales, United Kingdom. The tidal range of the site and the storm surge were randomly generated at the first stage of ISMC simulation from the probability distributions describing the phenomena. At the second stage, the damage probability was predicted by approximating the limit-state surface by a quadratic one having the identical curvature at the design point. Newport and Broadhaven revetments were safe, but the revetment at Wiseman's Bridge needed strong maintenance. The risk assessment model reflected the effect of water level changes (circa 6 m above ordnance datum) on the reliability of rubble mound revetments by simulating the environmental conditions at the sites. As the uncertainties inherent in design parameters were extensive, such as variations associated with wave data, tidal range and storm surge, it was suggested to determine the reliability of revetments by using Monte Carlo simulation methods. On the other hand, such hard engineering structures in a National Park Coast where the emphasis is on natural beauty are questionable, especially when they protect just two buildings, such as the Wiseman's Bridge revetment. It is ironic that pebble beaches abound in the area, and these are probably the best protection that can be given both to nature and structures.