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Authors

Mitchell D. Harley
Raimundo Ibaceta
Ian L. Turner
Kristen D. Splinter
Melissa A. Bracs
Yarran Doherty
Nashwan Matheen
Jason Middleton
Matthew S. Phillips
Kilian Vos
Andrew D. Short

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Corresponding Author

Mitchell D. Harley
School of Civil and Environmental Engineering
UNSW Sydney
Sydney, NSW, Australia

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Geographic Coverage

• Location: Narrabeen‑Collaroy Beach, New South Wales, Australia
• Approximate coordinates: 33.7° S, 151.3° E
• Beach length: ~3.6 km embayed sandy beach

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Temporal Coverage

• Start: 1930
• End: 2021
• Temporal resolution: sub‑daily to multi-decadal (method dependent)

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Data Files Included

1. Narrabeen_Shoreline_Dataset_v2.csv

Primary dataset containing all shoreline observations.

Each row represents a single shoreline point in space and time.

Columns

1. Row_ID
   Unique identifier for each shoreline data point.
2. Alongshore_location_s_m
   Alongshore distance from the northern end of the beach, defined relative to a logarithmic spiral fit of the embayment planform.
3. Shoreline_position_p_m
   Cross‑shore shoreline position relative to the logarithmic spiral reference line. This is the primary variable for shoreline‑change analysis.
4. Survey_method
   Codename identifying the technique used to derive the shoreline point.
5. Datetime_AEST
   Local date and time of shoreline measurement in ISO 8601 format (yyyy-MM-ddTHH:mm:ss+10:00). Local time is Australian Eastern Standard Time (AEST; UTC + 10). Where the acquisition time was unavailable or not meaningful (e.g. shorelines derived from observations spanning a tidal cycle), a nominal time of 12:00:00 AEST has been assigned. Refer to Time_flag.
6. Eastings_m
   Easting coordinate in GDA94 / MGA Zone 56 (EPSG:28356).
7. Northings_m
   Northing coordinate in GDA94 / MGA Zone 56 (EPSG:28356).
8. Bias_m
   Estimated cross-shore bias relative to the corresponding high-accuracy validation dataset (Bias = survey method − validation dataset).
9. Std_m
   Estimated cross-shore positional uncertainty expressed as the standard deviation relative to the validation dataset.
10. RMSE_m
    Estimated cross-shore positional uncertainty expressed as the root mean square error relative to the validation dataset.
11. Time_flag
    Flag indicating whether the acquisition time is known (Time_flag = 0) or assumed as 12:00:00 AEST (Time_flag = 1).
12. Interp_flag
    Flag indicating whether the shoreline point was derived directly from measurements (Interp_flag = 0) or by alongshore interpolation from sparse measurements (Interp_flag = 1).
13. Profile_ID
    Identifier indicating whether the shoreline point coincides with one of the five historical profile transects (PF1, PF2, PF4, PF6, PF8) or the fixed lidar transect (PFLD). Set to NA otherwise.

Version v1 represents the original dataset.

Version v2 includes ARGUS data between 2014-2021 at alongshore locations >3000m missing in v1. Also includes updated column names and merged datetime format for improved machine readability

Further versions and their changes will be documented.

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2. Bias‑Corrected ERA5 Wave Data

Bias_Corrected_ERA5_Waves_Sydney.csv

This file contains hourly deepwater wave conditions derived from the ERA5 global reanalysis and bias‑corrected using measured data from the Sydney directional waverider buoy. The data span 1940–2021 and represent conditions at the ERA5 node closest to Sydney.

Columns

1. Datetime_AEST
   Local date and time in AEST following ISO 8601 format (yyyy-MM-ddTHH:mm:ss+10:00)
2. Hsig_m
   Significant wave height (Hs), expressed in metres.
3. Tp_s
   Peak wave period, expressed in seconds.
4. Wdir_degTN
   Mean wave direction, expressed in degrees true north, following the oceanographic convention (direction waves propagate from).
5. Flag
   Indicator describing the directional regime used for bias correction. Flag = 0 indicates raw ERA5 wave directions between 30° and 210°, corresponding to the dominant onshore-directed wave sector at Narrabeen-Collaroy. Flag = 1 indicates raw ERA5 wave directions outside this range, corresponding to offshore-directed or highly oblique waves where ERA5 resolution effects are more pronounced. Both flag categories have been bias-corrected, but using different correction schemes.

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3. Astronomical Tide Data

Astronomical_Tide_Sydney.csv

This file contains astronomical tide levels for Sydney at 15‑minute intervals, spanning 1930–2021. The data are derived from harmonic analysis of long‑term tide gauge records and are intended to support shoreline derivation and tidal correction.

Columns

1. Datetime_AEST
   Local date and time in AEST following ISO 8601 format (yyyy-MM-ddTHH:mm:ss+10:00)
2. Tide_level_mAHD
   Astronomical tide elevation in metres relative to Australian Height Datum (AHD). Values represent predicted tidal variability only and do not include meteorological residuals such as storm surge, coastal trapped waves or atmospheric pressure effects. Note that 0 m AHD approximately corresponds to mean sea level.

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4. Cross-shore Transect Files

Narrabeen_Transects_Alongshore.csv
Narrabeen_Transects_Alongshore.geojson
Narrabeen_Transects_Profiles.csv
Narrabeen_Transects_Profiles.geojson

These files define the origins (p = 0) and orientations of each cross-shore transect used in the Narrabeen–Collaroy shoreline dataset. Transects are oriented approximately shore-normal (using the log-spiral fit of the beach planform) and are referenced by alongshore distance.

The two sets of files refer to transects spaced every 4 m alongshore (from s = 100 to s = 3600) in the same spacing as that of the shoreline dataset and a second set containing the 5 historical profile lines (PF1, PF2, PF4, PF6 and PF8) as well as the transect of the continuously scanning lidar (PFLD).

The CSV files contain tabulated transect coordinates in MGA94 / Zone 56 (EPSG:28356), while the GeoJSON files provide equivalent information as LineString geometries for direct use in GIS software (e.g. QGIS). 

Columns

1. Label
   Label string associated with the transect
2. Alongshore_location_s_m
   Alongshore distance of the transect in metres, measured relative to the dataset origin.
3. p0m_Eastings_m
   Easting coordinate (EPSG:28356) of the landward (origin) point of the transect, coinciding with the cross-shore distance p = 0 m.
4. p0m_Northings_m
   Northing coordinate (EPSG:28356) of the landward (origin) point of the transect, coinciding with the cross-shore distance p = 0 m.
5. p200m_Eastings_m
   Easting coordinate (EPSG:28356) of a seaward (p = 200 m) point along the transect that helps define the transect orientation.
6. p200m_Northings_m
   Northing coordinate (EPSG:28356) of a seaward (p = 200 m) point of the transect that helps define the transect orientation.

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5. Intertidal beach face slope

Narrabeen_Intertidal_Slopes.csv

This file contains intertidal beach face slope values (m) along the beach, derived from QUADBIKE three-dimensional survey data between 2005 and 2016.

Columns

1. Alongshore_location_s_m
   Alongshore distance of the transect in metres, measured relative to the dataset origin.
2. Datetime_AEST
   Alongshore distance of the transect in metres, measured relative to the dataset origin.
3. m_slope
   Intertidal beach face slope m, defined by a linear fit at each alongshore location between 0 m AHD and 1.2 m AHD, following https://doi.org/10.1002/2014JF003390.

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Survey Methods

Shoreline positions are derived from thirteen monitoring techniques, grouped as follows:

Shorelines from Instantaneous Waterlines

AIRPHOTO, NEARMAP, COASTSAT, PLANETSCOPE, COASTSNAP

Shorelines from Intertidal Waterlines

ARGUS, ARGUSNN

Shorelines from Elevation Data

EMERYPFS, RTKPFS, RTKSTORM, FIXEDLIDAR, QUADBIKE, AIRLIDAR

All shoreline positions correspond to a fixed elevation of 0.7 m AHD, approximately equivalent to mean high-water springs at this micro-tidal site. Elevations from source datasets referenced to ellipsoidal heights were transformed to the Australian Height Datum (AHD) using AUSGEOID09.

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Coordinate Reference Systems

• Horizontal CRS: GDA94 / MGA Zone 56 (EPSG:28356)
• Derived CRS: Alongshore–cross‑shore (s, p) system based on a logarithmic‑spiral fit to the embayment planform (https://doi.org/10.1016/j.coastaleng.2007.07.001)

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Data Quality and Validation

Shoreline positional accuracy varies by method and alongshore location. Accuracy metrics (bias, standard deviation, RMSE) are quantified through comparisons with high‑accuracy reference datasets (RTK‑GNSS and airborne lidar), using same‑day or temporally constrained observations. Location‑specific uncertainty estimates are retained in the dataset.

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Usage Notes

Each shoreline monitoring technique involves trade‑offs between temporal resolution, accuracy, spatial coverage, and record length. Users are encouraged to:

• Combine multiple methods to resolve both storm‑scale and long‑term variability
• Use high‑frequency datasets (e.g. ARGUS, FIXEDLIDAR) for event‑scale studies
• Use long‑term datasets (e.g. AIRPHOTO, EMERYPFS/RTKPFS) for multi‑decadal trend analysis

Interpolated shorelines derived from transect data are explicitly flagged.

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Relationship to Existing Datasets

Cross‑shore positions in this dataset are referenced to a logarithmic‑spiral origin, differing from the benchmark‑referenced origin used in the long‑running Narrabeen beach profile dataset (https://doi.org/10.5061/dryad.28g01). Published offsets must be applied before datasets are combined.

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Code Availability

Example Jupyter notebooks demonstrating data access, filtering, and visualisation are available at:
https://github.com/mitchharley/Narrabeen-Shorelines

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Citation

Users must cite both this Dryad dataset and the associated Scientific Data Data Descriptor when using these data.

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License

This dataset is distributed under the license specified in the Dryad repository record.