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

Abstract

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.

Climate controls on longshore sediment transport

“…As observed on other wave-dominated coasts, a strong seasonal signal in the shoreline is present (Davidson and Turner, 2009). Net longshore transport for the region is frequently quoted as 500,000 m 3 /yr to the north (Dyson et al, 2002;Patterson, 2007;Castelle et al, 2009), referring to the seminal studies completed by Delft Hydraulics Laboratory (DHL, 1970(DHL, , 1992. However, spatial and temporal variations in this estimate are present due to spatial variation in wave exposure and sediment supply (Patterson, 2007).…”

“…The Tweed River by-passing system transports sand from Letitia Spit, New South Wales (Fig. 1, ETA 08) to several sites between Duranbah Beach and Kirra Point, Queensland, depending on prevailing beach conditions (Dyson et al, 2002;Castelle et al, 2009 coast. An artificial reef is located offshore of Narrowneck at ETA 67 to provide additional shoreline protection and additional surfing amenity (Turner, 2006) .…”

“…Both the Nerang and 5 Tweed River entrances have training walls that disrupt the longshore transport such that sand by-passing systems have been installed at both sites. Historical pumping rates vary between 400,000 m 3 /yr and 800,000 m 3 /yr (Patterson, 2007;Castelle et al, 2009). The Tweed River by-passing system transports sand from Letitia Spit, New South Wales (Fig.…”

Climat de houle et caractéristiques morpho-sédimentaires du littoral de Bouknadel-Kénitra (Maroc)

“…Afin d'estimer la quantité de sable transporté le long de la plage, nous nous sommes basés sur la formulation proposée par KACZMAREK et al (2005). Cette formule a été choisie en raison de son nombre limité des paramètres ajustables et aussi parce qu'elle a été utilisée et validée par BERTIN et al (2008) et CASTELLE et al (2009 …”

“…où est l'angle d'incidence des vagues au point de déferlement, est l'indice de déferlement de BATTJES & JANSSEN (1978), k v une constante empirique fixée à 2,9 (BERTIN et al, 2008 ;CASTELLE et al, 2009). Les conditions au point de déferlement (H b , ) sont déterminées à partir de la loi de Snell-Descartes combinée à la formule de RATTANAPITIKON & SHIBAYANA (2000).…”