Impact of Brunswick River Mouth Training Walls on Adjacent Beaches, Brunswick Heads, New South Wales, Australia

River training walls have been built at scores of locations along the NSW coast and their impacts on shoreline change are still not fully understood. In this study, the Brunswick River entrance and adjacent beaches are selected for examination of the impact of the construction of major training walls. Thirteen sets of aerial photographs taken between 1947 and 1994 are used in a GIS approach to accurately determine the shoreline position, beach contours and sand volumes, and their changes in both time and space, and then to assess the contribution of both the structures and natural hydrodynamic conditions to large scale (years-decades and kilometres) beach changes. The impact of the training walls can be divided into four stages: natural conditions prior to their construction (pre 1959), major downdrift erosion and updrift accretion during and following the construction of the walls in 1959-1962 and 1966, diminishing impact of the walls between 1966 and 1987, and finally no apparent impact between 1987-1994. The impact extends horizontally about 8 km updrift and 17 km downdrift, and temporally up to 25 years.