ICE - Institution of Civil Engineers - Virtual Library

In risk assessment, the second-order reliability method (SORM) and the conditional expectation Monte Carlo (CEMC) simulation were inter-related in order to analyse the safety of Brean and Newton revetments on the south and north coasts of the Inner Bristol Channel, South Wales, UK. In the CEMC simulation, storm surge and wave height were generated as correlated random variables with probability distributions describing the phenomena. Then, damage probability was predicted by approximating the limit state surface by a quadratic one having the identical curvature at the design point. It was found that revetment reliability was sensitive to tidal range, storm surge and wave data. Brean revetment was found to be safe, whereas maintenance works were required during the service life of Newton revetment. The model introduced a new technique into the reliability assessment of revetments subject to large tidal ranges and its predictions satisfactorily reflected the safety/damage conditions of the structures at the site

The removal of sediment from estuaries by maintenance dredging has the potential to be detrimental to habitats such as saltmarshes. This paper examines the case for environmental reparation with respect to maintenance dredging activities in two estuaries within the western Solent in England. These two examples suggest that the detrimental impacts of maintenance dredging and requirement for beneficial use schemes may have been overstated in some areas of the UK. The examples also demonstrate that beneficial use schemes themselves can potentially have deleterious impacts on estuary systems and therefore should not be viewed as a universal panacea for estuary management.

The wash produced by a ship's rotating propeller is known to cause scouring of the seabed. The design of suitable armour units to prevent such scouring requires an understanding of the velocities within the wash. Key to predicting velocity at any position within the wash is an accurate method for determining the maximum velocity as the wash exits the propeller. This value is known as the efflux velocity. This paper details a study that was undertaken to provide a means by which a more accurate estimation of this velocity can be obtained.

Ship effects at the bankline are most significant in confined channels and many ship channels contain a shallow berm on one or both sides of the channel. The shallow berm has a large impact on the ship effects at the bank-line. The dominant ship effects in confined channels are caused by the displacement effects of the ship and include long-period effects of drawdown, return velocity, transverse stern wave, and surge. Ships generally operate at 80–90% of limit speed and the displacement effects of the ship vary significantly with speed in this range. Analytical/empirical methods cannot address ship effects where shallow berms exist or complex channels. A numerical model, HIVEL2D, is used to determine ship effects in complex confined channels. Model-prototype comparisons show agreement of long-period effects such as drawdown. An empirical relationship is developed for determining surge magnitude but is limited to the waterway on which it was developed until additional data can be collected.