Coastal Engineering Aspects in the Design of the Seawall for Sydney Airport's Parallel Runway

Sydney's parallel Runway project incorporated major dredging and reclamation of some 15 million cubic metres of sand within Botany Bay and construction of over 7 km of seawall and river diversion works using reinforced soil technology. The paper focuses on the coastal engineering aspects in the development of the seawall to meet a number of criteria including minimisation of wave overtopping and wave spray carryover and security against wave scour at the wall foundation. The solution developed included an integral, curved wave deflector cast into the top panels of the seawall, a secondary wave barrier set 5 to 10m in from the seawall, an overtopping pavement between the seawall and the secondary barrier and various natural and proprietary forms of scour protection at the base of the wall. Investigations in developing the design included joint probability analysis of historical wind and tidal records to determine realistic design water level/wave height combinations; two dimensional laboratory wave flume testing to examine wave overtopping, wave spray carryover and base scour behaviour for the seawall; three dimensional laboratory wave basin testing to examine the effects of non-orthogonal wave action on the seawall; As a result of the testing and analysis, optimal seawall sections were developed for the different exposure conditions around the seawall. Since construction, the wall has been subjected to a number of medium level storm events and its performance to dare has vindicated the efforts put into this important aspect of the project.