Historical charts, soundings and surfaces (DEMs) of western Victoria, Australia
Description
This data repository hosts the georeferenced nautical charts, digitised soundings, converted soundings (Australian Height Datum 1994), surface masks and interpolated surfaces (DEMs) of seven historical surveys conducted in western Victoria during the 19th century. These charts produced by H. J. Stanley, J. Barrow and J. B Mason for Portland Bay (1854, 1869 and 1972), Port Fairy (1870), Lady Bay-Warrnambool (1870) and Apollo Bay (1868 and 1889), were obtained in digital format from the State Library Victoria (www.slv.vic.gov.au). For specific characteristics of individual charts refer to Table 1. These nautical charts provide an unique historical perspective of the coast during the time of the surveys. These datasets were used by the author and collaborators to understand sedimentary dynamics and quantify human alterations in the coastal zone, by comparing their surfaces to contemporary Multibeam Echosounding (MBES) bathymetry and Light Detection and Ranging (LiDAR) data. The georeferenced nautical charts and interpolated surfaces are in Geotiff format, and the digitised soundings, converted soundings and surface masks are in shapefile format. Files are compressed and organised in sub-folders inside specific charts.
Files
Steps to reproduce
Georeferencing of historical charts was conducted with a minimum of four and a maximum of 11 ground control points (Table 2). Due to poor representation of the coastline and land features within the Portland Bay 1854 and 1872 charts, high RMSEs of 25.7 m and 17.5 m, respectively, were obtained. The lowest RMSEs (1.6 m) was obtained for the Port Fairy 1870 chart. Area covered by the digitised depth points ranged from 1.2 km2 (Apollo Bay 1889) to 76 km2 (Portland Bay 1854). Minimum and maximum depths in original charts units were 0.167 (1/6) of a foot (Port Fairy 1870 and Lady Bay 1870) and 31 fathoms (Apollo Bay 1868), respectively. Following digitisation of individual sounding points and tabulation of values, the original sounding units were converted to meters (1 fathom = 1.829 m and 1 foot = 0.305 m). Then, a vertical datum transformation was conducted using AusCoastVDT v1.20 (SeaGIS, 2019). Vertical separation grid file 25092019.VDTGrid was used for these transformations. This converted all depths in the original chart datums to the Australian Height Datum (AHD) 1994. For that, the vertical datum of LWST, LWOST and the unknown datum of Portland Bay 1854 and Apollo Bay 1868 charts were considered equivalent to Mean Low Water Springs (MLWS), whereas the HWF&C datum of Portland Bay 1872 and Lady Bay 1870 were considered equivalent to Mean High Water Springs (MHWS). Datum transformation yielded a maximum difference of 0.83 m between the original vertical datum and AHD 1994. DEMs for each historical chart were created by interpolating individual sounding depths in ArcMap v.10.7 using the Inverse Distance Weighted (IDW) tool with a variable search radius for 12 sample points (default) and 10 m pixel size. A mask delimiting the sounding area in each chart was used to define the extent of the interpolations. These masks excluded major unsurveyed intertidal and subaerial areas such as islands, rock reefs and non-existent man-made structures (breakwater, wharf, viaduct) in the 19th century.