Beach nourishments at Coolangatta Bay over the period 1987 – 2005 : Impacts and lessons

Erosion of the southern Gold Coast beaches (SE Queensland, Australia) was exacerbated after the extension of the Tweed River training walls in the early 1960s. To achieve the objective of restoring and maintaining beach amenity, significant nourishment works have been undertaken in Coolangatta Bay over the past 30 years. Particularly, under the Tweed River Entrance Sand Bypassing Project (TRESBP) since 1995, a number of nourishment campaigns and the implementation of a permanent sand bypass system in 2001 have resulted in significant changes of Coolangatta Bay morphology. The present case study investigates the influence of both wave climate and nourishment works on the area extending from the updrift Snapper Rocks area to downdrift Kirra Beach. SWAN spectral wave model is implemented at Coolangatta Bay area and forced by the global wave model WW3 to estimate wave forcing and the potential natural longshore drift entering in Coolangatta. Specific transects extracted from accurate bathymetric surveys are used to investigate and quantify Coolangatta Bay sedimentation for the period 1987-2005. A network of Argus video stations provides high sample rate information on the shoreline evolution. Results show that, over the past 10 years, Coolangatta Bay has infilled rapidly. Sedimentation reached up to 6 m in some areas between 1995 and 2005, with beach width increasing by 200 m at Kirra Beach. Rapid seaward shoreline migration is consistent with the intense over-pumping of sand relative to the natural potential to move sand alongshore. The nourishment strategy used during this project has successfully delivered large amounts of sand to the southern Gold Coast embayment, although it has been up to now controversial from many community perspectives. The artificial sand bypassing process proved to be much more efficient than depositing the dredged sand in the nearshore area which requires a significant period of low energy condition in order for the deposited sediment to migrate shoreward and weld to the shore. This case study confirms that, when carefully undertaken, sand bypassing is a sustainable and flexible soft engineering approach which can work in concert with natural processes. Bea h nourishments at Coolangatta Bay over the period 1987-2005: impa ts and lessons Bruno Castelle 1,4 Ian L. Turner 2 Xavier Bertin 3 Rodger Tomlinson 1 Email address: b. astelle epo .u-bordeaux1.fr (Bruno Castelle). 1 Gri th Centre for Coastal Management, Gold Coast Campus, Gri th University, PMB 50 Gold Coastal Mail Centre, Queensland 9726, Australia 2 Water Resear h Laboratory, S hool of Civil and Environmental Engineering, University of New South Wales, NSW 2093, Australia 3 National Civil Engineering Laboratory, Estuaries and Coastal Zones Division, 1700-066, Lisbon, Portugal 4 Université Bordeaux I, CNRS, UMR 5805-EPOC, Avenue des Fa ultés, Talen e, F-33405, Fran e Preprint submitted to Elsevier July 30, 2008 * Manuscript Click here to view linked References Abstra t Erosion of the southern Gold Coast bea hes (SE Queensland, Australia) was exa erbated after the extension of the Tweed River training walls in the early 1960s. To a hieve the obje tive of restoring and maintaining bea h amenity, signi ant nourishment works have been undertaken in Coolangatta Bay over the past 30 years. Parti ularly, under the Tweed River Entran e Sand Bypassing Proje t (TRESBP) sin e 1995, a number of nourishment ampaigns and the implementation of a permanent sand bypass system in 2001 have resulted in signi ant hanges of Coolangatta Bay morphology. The present ase study investigates the in uen e of both wave limate and nourishment works on the area extending from the updrift Snapper Ro ks area to downdrift Kirra Bea h. SWAN spe tral wave model is implemented at Coolangatta Bay area and for ed by the global wave model WW3 to estimate wave for ing and the potential natural longshore drift entering in Coolangatta. Spei transe ts extra ted from a urate bathymetri surveys are used to investigate and quantify Coolangatta Bay sedimentation for the period 1987-2005. A network of Argus video stations provides high sample rate information on the shoreline evolution. Results show that, over the past 10 years, Coolangatta Bay has in lled rapidly. Sedimentation rea hed up to 6 m in some areas between 1995 and 2005, with bea h width in reasing by 200 m at Kirra Bea h. Rapid seaward shoreline migration is onsistent with the intense over-pumping of sand relative to the natural potential to move sand alongshore. The nourishment strategy used during this proje t has su essfully delivered large amounts of sand to the southern Gold Coast embayment, although it has been up to now ontroversial from many ommunity perspe tives. The arti ial sand bypassing pro ess proved to be mu h more e ient than depositing the dredged sand in the nearshore area whi h requires a signi ant period of low energy ondition in order for the deposited sediment to migrate shoreward and Preprint submitted to Elsevier July 30, 2008 weld to the shore. This ase study on rms that, when arefully undertaken, sand bypassing is a sustainable and exible soft engineering approa h whi h an work in on ert with natural pro esses.