Long-term datasets that record and quantify the variability, changes and trends in morphology observed at sandy beaches are rare. A monthly beach profile survey program that commenced in April 1976 at Narrabeen located on Sydney's Northern Beaches is one of a limited number of sites globally where on-going and uninterrupted beach monitoring now spans multiple decades.

In the 1970s and 1980s the growing database of beach surveys at Narrabeen was key to the pioneering work by Australian coastal geomorphologists that resulted in the formulation of a morphodynamic Beach State Model. This model remains today as the standard classification scheme used by coastal scientists worldwide to describe different natural beach states, their characteristic morphodynamic process signatures and associated wave and sediment environmental controls.

During the 1990s related studies at Narrabeen included a focus on surfzone rip currents and the emergence of new insight to the associated hazards to beach swimmers. At the turn of the 21st Century the record of beach changes at Narrabeen had extended to sufficient length that longer-term cycles and underlying trends in beach behaviour began to be revealed. This prompted significant new interest in the wider use of the Narrabeen survey dataset to further identify and explore potential linkages between regional-scale climatic forcing and sandy coastline response. At the same time, recognition within the research community that regional-scale wave climates can be expected to change and sea levels in the coming decades will continue to rise, helped strengthen the awareness of the fundamental importance of sustained coastline monitoring programs. In particular, the monthly observations from Narrabeen provided an all-too-rare data resource to calibrate and test new models aimed at developing better prediction tools of present and future variability and changes along sandy coastline worldwide.

The monthly beach profile survey program at Narrabeen reached its 40-year milestone in April 2016. Online access to this dataset now facilitates its unrestricted use by the international coastal research community. It is envisaged that open access to these data may provide additional stimulus to coastal morphodynamic modellers to develop, test and (it is hoped) significantly advance the next generation of beach erosion-recovery hindcasting and forecasting tools. It is also hoped that this website can be a useful educational resource for students and teachers. As a discipline, our ability to predict anticipated coastal changes in the context of a changing climate is presently in its relative infancy. In the meantime, as the current custodians of this unique resource, it is the intention that collection of monthly profile data at Narrabeen will continue for the foreseeable future and be provided here, as our contribution to generations who follow.

The beach monitoring program at Narrabeen can be divided into two distinct periods: the first three decades when a simple and traditional survey technique was employed; and from 2004 onwards when the monitoring program was significantly expanded, and the use of new and emerging survey technologies have been progressively implemented. A time-line and summary of the various survey methods employed is described below.

1976-2006: historical profile surveys

The years between 1976 and 2006 constitute the period of conventional profile line surveys undertaken by Professor Andrew Short and volunteers of the Coastal Studies Unit, University of Sydney, employing the Emery method. This simple, rapid and low-cost technique uses a measuring tape for cross-shore distance, and vertical elevation changes are calculated using line-of-sight between two graded rods and the horizon. Commencing with the landward rod on a fixed benchmark, the distance between the two rods is first measured using the measuring tape. The change in elevation between the two rods is then calculated by using the line-of-sight with the horizon and markings on the rods as a reference. This process is repeated at each subsequent measurement point along the entire length of the cross-shore profile line.

The Emery method for measuring beach profiles

The monitoring program during the 1970s based on this use of the Emery method initially comprised fortnightly cross-shore profile surveys at a total of fourteen profile lines along the embayment. Each profile line was surveyed at spring low tide from a fixed benchmark located in the stable dune area down to a swimming depth within (and sometimes beyond) the surf zone. This labour-intensive approach typically extended each surveyed profile to depths of 1 - 4 m below mean sea level, depending on the prevailing surf conditions. The cross-shore spacing of each measurement was 10 m.

Following the first few years of these fortnightly surveys at fourteen profile lines, a pragmatic decision was made to reduce and focus on-going effort to achieve monthly surveys at a lesser number of five representative profile lines. These five profiles that continue to the present day are numbered 1, 2, 4, 6 and 8 (north to south, hereafter identified as PF1, PF2, PF4, PF6 and PF8); their non-sequential numbering corresponds to the original numbering scheme when 14 profiles were surveyed. The seaward survey limit for each of these five representative profiles was also changed to the more easily achievable intersection with mean sea level (i.e., approximately wading depths). These early and pragmatic decisions to limit the number and cross-shore extent of each profile line are undoubtedly the key reasons why monthly surveys were subsequently achieved by the same personnel during the ensuing three decades.

2004-present: new survey techniques

Recognising the unique and growing value of the Narrabeen survey dataset worldwide, beginning in 2004 efforts were initiated by the UNSW Water Research Laboratory to secure, improve and expand the monitoring program into the future through the use of new survey technologies. This commenced in July 2004, with the decision to transition the historical profile line surveys from the Emery method to the use of high-accuracy RTK-GPS technology (vertical accuracy ≈ ± 0.03 cm). Following an 18-month validation period during which surveys were undertaken concurrently using the Emery method and RTK-GPS, the use of RTK-GPS as the standard survey method for the five profile lines was adopted in August 2006. The cross-shore resolution of each profile survey was also increased at this time from the original 10 m measurement spacing to near-continuous (i.e., approximately every 0.10 m cross-shore).

Narrabeen-Collaroy coastal monitoring team, 2015

At the same time as the use of RTK-GPS was implemented in early 2004, an Argus coastal imaging station was installed atop the 44 m high Flight Deck apartment building at South Narrabeen. Since this time, this station has continuously collected hourly daylight images of the southern sector of the beach from five separate cameras (the field of view encompassing PF6 and PF8). Automated algorithms are used to measure high-frequency shoreline variability and other beach and surfzone features.

Since 2004 several additional survey techniques have been progressively implemented at Narrabeen to complement the on-going monthly profile surveys detailed here, with the objective to build an expanded future dataset with which to gain greater understanding of beach morphodynamics at more detailed spatial and temporal resolutions. These techniques include:

Monthly three-dimensional RTK-GPS surveys of the entire subaerial beach using an all-terrain vehicle
A second Argus coastal imaging station installed at the northern end of the beach
Pre- and post-storm three-dimensional Airborne Lidar surveys of the entire beach and dune systems
A permanent fixed Lidar system scanning a single profile line day and night at a frequency of 5 Hz
Pre- and post-storm three-dimensional surveys of the entire beach and dune systems using an Unmanned Aerial Vehicle
Single and multi-beam bathymetric surveys of the surf zone and offshore bathymetry

The coastline of southeastern Australia includes over 700 embayed sandy beaches averaging 1.3 km in length separated by rocky headlands. The 3.6 km-long Narrabeen-Collaroy embayment (hereafter simply referred to as ‘Narrabeen’) is situated within the Northern Beaches region of metropolitan Sydney. Locally, the sandy beach that spans the entire embayment is referred to as Narrabeen beach towards the north and Collaroy beach in the south, with the small section of beach adjacent to the prominent headland at the extreme southern end called Fishermans beach (see right).

The beach sediments at Narrabeen were deposited as a regressive barrier in the mid- Holocene approximately 300 m landward of the present-day shoreline. The barrier subsequently prograded through a series of foredune ridges, with the most seaward ridge of the modern embayment dated at 3 ka. The granulometry is approximately uniform along the beach and characterized by fine to medium quartz sand (D50 ≈ 0.3 mm) with ~30% carbonate fragments. A lagoon now backs the northern half of the barrier and is connected to the ocean via a shallow narrow (~50 m-wide) inlet at the embayment’s northern extremity that intermittently opens and closes to the ocean.

The adjacent headlands and curvature of the embayment result in a distinctive alongshore wave energy gradient. Dissipative-intermediate beach conditions typically prevail in the north, transitioning to lower energy and intermediate-reflective beach conditions towards the south. The northern end of Narrabeen is characterised by single-bar rhythmic bar-beach (RBB) to transverse bar-rip (TBR) intermediate beach states and a subaerial berm that varies up to 80 m in width, backed by a vegetated foredune up to 9 m in height above mean sea level (MSL). At the southern end of the embayment urban development has encroached on to much of the foredunes, which reach only 3 to 4 m in height, and the beach consists of a berm that varies up to 60 m in width and a single-bar system that tends towards the lower energy low-tide terrace (LTT) and reflective beach states.

Tides are microtidal and semidiurnal with a mean spring tidal range of 1.3 m. The deepwater wave climate for the Sydney region is of moderate to high wave energy (mean Hs ≈ 1.6 m and Tp ≈ 10 s) and dominated by persistent long period swell waves from a SSE direction. These swell waves are generated from mid-latitude cyclones that propagate approximately 5-9 times per month across the southern Tasman Sea, south of mainland Australia. Superimposed on these background swell waves are storm events that are typically defined for this region by a significant wave height threshold of 3 m, corresponding to the 0.95 quantile. These storm waves are derived from a number of sources and directions: tropical cyclones from the northeast, east-coast lows from the east and intensified mid-latitude cyclones from the south. The wave climate exhibits a mild seasonal cycle, with high-energy mid-latitude cyclones and east-coast lows more prominent in the Austral winter months and low-energy short-period seas derived from local north-easterly sea-breezes more prominent in the Austral summer. At inter-annual time scales, the wave climate is influenced by the El Niño/Southern Oscillation (ENSO), with La Niña periods typically having a more energetic and easterly wave climate and El Niño periods a less energetic and more southerly wave climate.

The distinct wave energy gradient in the local shallow-water wave climate at Narrabeen is to a large degree a result of the sheltering of southerly waves by the 1.5 km Long Reef Point headland that forms the embayment’s southern extremity. Numerical wave modeling indicates breaking wave height is approximately 30% higher at the northern end compared to the southern end for average wave conditions. This situation is reversed, however, for northeast waves, with breaking wave heights approximately 30% larger in the south relative to the north. An equivalent reversal in the wave angle of incidence is also observed, with southerly waves resulting in northerly-directed alongshore currents and northeast waves resulting in southerly-directed alongshore currents.

Data Descriptor

In addition to the growing dataset of monthly beach profiles available at this web site, an archived dataset for the fixed period 1976 – 2014 is described and detailed in the accompanying peer-reviewed Data Descriptor paper, published in the journal 'Scientific Data' (Nature Publishing Group). This comprehensive dataset includes monthly subaerial profiles, bathymetries, and time-series of astronomical tide and offshore wave forcing transformed to the inshore location corresponding to each of the individual survey transects.

Acknowledgements

Since 2004 the continuing beach monitoring program has been funded by the Australian Research Council (Discovery and Linkage), Warringah Council, NSW Office of Environment and Heritage (OEH), SIMS Foundation, the UNSW School of Civil and Environmental Engineering and the UNSW Faculty of Engineering. OEH provided the bathymetry data included here. The Sydney waverider buoy data used for offshore to inshore wave transformation is funded by OEH and managed by Manly Hydraulics Laboratory. The SWAN lookup table to complete this transformation was initially created by Mr Ed Kearney. CSIRO (especially Dr Mark Hemer) is acknowledged for undertaking and providing the CAWCR wave hindcast dataset. Brad Morris of OEH provided the Sydney tide measurements for T_Tide analysis. Brett Miller at UNSW provided guidance on the creation of this website. And finally, we would like to thank all those individuals who have joined us on the beach to assist with the monthly surveys during the past 4 decades.

Overview

Historical Survey Program

1976-2006: historical profile surveys

2004-present: new survey techniques

Site Description

Data Descriptor

Acknowledgements