A multi-decade dataset of monthly beach profile surveys and inshore wave forcing at Narrabeen, Australia

Abstract

Long-term observational datasets that record and quantify variability, changes and trends in beach morphology at sandy coastlines together with the accompanying wave climate are rare. A monthly beach profile survey program commenced in April 1976 at Narrabeen located on Sydney’s Northern Beaches in southeast Australia is one of just a handful of sites worldwide where on-going and uninterrupted beach monitoring now spans multiple decades. With the Narrabeen survey program reaching its 40-year milestone in April 2016, it is timely that free and unrestricted use of these data be facilitated to support the next advances in beach erosion-recovery modelling. The archived dataset detailed here includes the monthly subaerial profiles, available bathymetry for each survey transect extending seawards to 20 m water depth, and time-series of ocean astronomical tide and inshore wave forcing at 10 m water depths, the latter corresponding to the location of individual survey transects. In addition, on-going access to the results of the continuing monthly survey program is described.

The June 2016 Australian East Coast Low: Importance of Wave Direction for Coastal Erosion Assessment

“…Long-term beach monitoring [15] also shows that the 2016 storm led to the largest eroded subaerial beach volume at Narrabeen-Collaroy since recording began in 1976. Erosion of the subaerial beach was not explicitly modelled here because of insufficient information on the pre-storm beach condition.…”

“…This is based on the Subaerial Beach Volume Index (SVI), a ratio of the dry beach volume relative to the long-term mean [15]. Prior to the April 2015 event, the beach was close to the mean state (SVI + 2.6), but after the storm it had been reduced to −24.9 (a net change of 27.5).…”

“…Pre-and post-storm beach surveys (above the water line) were undertaken at Narrabeen-Collaroy by University of New South Wales as part of a long-term beach monitoring program [15]. Shore-normal transects were surveyed at five locations along the beach using GPS, each extending from the dune behind the beach down to the water line.…”

“…A mosaic of best-available bathymetries was used to generate a seabed topography in the model, including the pre-storm hydrographic survey undertaken at Narrabeen-Collaroy [21]. Bathymetric data also included a series of The coastal planform and elevation of the subaerial beach was idealized using the pre-storm cross-shore profile data from the Narrabeen beach monitoring program [15], and recent aerial photography. The dry beach was included in the model to provide a sediment source for storm cut and for flooding and drying at the shoreline.…”

“…Beach erosion and accretion trends have been monitored here since 1976 [15] and have been shown to be synchronous with other beach compartments along the NSW coast [16,17]. Despite being well recognised as an erosion hot spot, the shorefront of Collaroy is characterised by a legacy of inappropriate development into the active beach zone [18].…”