Patterson, D.C. Sand Transport and Shoreline Evolution, Northern Gold Coast, Australia. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 147 – 151. Gold Coast, Australia, ISSN 0749.0208
A net onshore supply of sand appears to exist along the northern Gold Coast beaches, resulting from an offshore profile shape at depths between 12-20 m that is flatter than that expected for dynamic equilibrium, a residual feature from past northward migration of the Nerang River mouth. Analysis of survey data over the period 1966 to 2002 shows progressive depletion of the lower profile (depths > 7.5 m out to 20 m) due to onshore supply and a substantial gain in the sand volume in the upper part of the nearshore and beach profile (depths < 7.5 m). Additionally, this section of shoreline has been nourished with about 3.7 million cubic metres of sand over the period 1974 to 2000, including an estimated 0.75 million placed from building sites.
However, despite the beach nourishment undertaken, the total volume of sand in the profile along the 10km section of beach analysed is only about 0.3 million cubic metres greater in 2002 than in 1966, indicating a corresponding local increase in the alongshore loss of sand. The reported historical changes and analysis of the longshore sand transport regime suggests that the evolution of the alignment of shoreline of the Spit has been commensurate with such a local increase of about 80,000 m3/yr in the longshore transport rate north of Narrowneck, increasing to about 90,000 to 100,000 m3/yr due to more recent beach nourishment works. This was matched initially by equivalent losses into the Broadwater and, following Seaway development, by a ‘leakage’ of sand past the bypass system and growth of the river entrance bar.
Beach management considerations need to account for these processes. The assessment undertaken supports the strategy of back-passing sand from the Seaway to the beaches to overcome future depletion of the onshore supply and associated recession of the shoreline alignment.
