Design of coastal structures - transforming Bunbury waterfront

Bunbury is a major regional centre in Western Australia (WA). Due to significant regional population growth, Bunbury is experiencing a critical and growing shortage of maritime facilities for small vessels, both recreational and commercial. Stage 3 of the Transforming Bunbury's Waterfront (TBW) project includes a major redevelopment of the Department of Transport's Casuarina Boat Harbour. The coastal structures required to support this redevelopment included a new breakwater and marine precinct at the entrances to Casuarina Boat Harbour (Northern Breakwater), an eastern breakwater for Koombana Yacht Club and refurbishment of five existing rock armoured structures. The existing structures adjacent to Casuarina Boat Harbour are located within the historic Port of Bunbury, with the original port breakwaters constructed in the 1890s and then extended on at least six occasions. The structures on the ocean (west) side provide important protection from large Indian Ocean waves and have had limited maintenance over the years. The southern portion of the original port breakwater is known locally as the BP Seawall and has been buried by accreting sand dunes. Sand penetrometer and geophysical investigations were subsequently undertaken to determine the extent of refurbishment required. Designs for refurbishment of the old BP Groyne, which has fallen into disrepair, and the Outer Harbour Seawall, subject to significant wave overtopping, have also been undertaken. Within Koombana Bay, marine geotechnical investigations were undertaken to better determine the extent and composition of soft marine sediments overlying a submerged basalt layer. This has required a number of design responses for the Northern Breakwater in-terms of scour protection and future settlement. Designs for revetments protecting future residential and marine precincts inside Casuarina Harbour has required consideration of response to ground conditions, reuse of existing materials, adjacent development levels for coastal flooding and future sea level rise, and integration with marine structures and public recreational waterfront areas.