Beach nourishment pattern-placement along the Gold Coast

The City of Gold Coast beach nourishment project placed 3 million m3 of sand from its offshore sand reserves into the surf-zone, along 10km of coastline. The nourishment consisted of the placement of individual artificial sand banks or a ‘sand pattern’. Weekly placement instructions were informed by a Beach Nourishment Framework. The Framework was a decision support system (computer program) which allowed continuous and systematic assessment of over 350 placement boxes to balance operational, morphological, social and environmental outcomes. Numerical modelling of sand patterns, weather forecasts, and surveys were considered in preparing the placement schedule. The resulting placement was performed in a complex sequence by dredge rainbowing in the surf-zone and by hopper release onto the bar. The dredge moved up and down the coast fortnightly. This innovative methodology allowed regular feeding of the sand patterns, to reduce beach use interruptions and to safeguard nourishment production. The sand pattern placement increased the beach profile in stages, providing sand to the nearshore progressively to maintain desirable beach amenity, and also to promote positive surfing outcomes. The pattern placement created short-lived bars and long-lived nearshore coastal deposits. At a larger-scale, the nourishment pattern included a range of A-frames, rhythmic patterns, nearshore sandbanks, and bomboras which were consistent with beach protection objectives. At a small-scale, the monitoring of “fresh” and “weathered” sand patterns (from daily multibeam surveys and regular LiDAR survey), allowed detailed observations of the evolution of the surf-zone and of the beach during the nourishment campaign. The motion of sand within the sand patterns was driven by wave-generated turbulences. Sand transport during the nourishment works was dominated by cross-shore profile evolution. Longshore transport contributed to lateral sand diffusion and triggered the movement of sand to the intertidal beach