Fig 1.
Study area topography and key placenames.
A) Elevation above sea-level from the NASA Digital Elevation Model (DEM [29]) and overlaid with local fluvial systems as represented by the HydroSHEDS Free Flowing Rivers dataset [30] B) Geological map of the study area (modified from [27]).
Table 1.
List of VHR images and associated metadata per study site.
Fig 2.
Shoreline change for the wider Apollonia area (Landsat: 1985–2020).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI as obtained from Landsat imagery. Quantified LRR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Label Apollonia indicates the ancient site. Basemap: Sentinel-2 (from the Copernicus Program; 2020 annual composite created using GEE).
Table 2.
Summary DSAS results based on Landsat imagery for wider areas around Apollonia, Ptolemais and Tocra.
Fig 3.
Shoreline change for the wider Ptolemais area (Landsat: 1985–2020).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI as obtained from Landsat imagery. Quantified LRR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Label Ptolemais indicates the ancient site. Basemap: Sentinel-2 (from the Copernicus Program; 2020 annual composite created using GEE).
Fig 4.
Shoreline change for the wider Tocra area (Landsat: 1985–2020).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI as obtained from Landsat imagery. Quantified LRR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Label Tocra indicates the ancient site. Basemap: Sentinel-2 (from the Copernicus Program; 2020 annual composite created using GEE).
Fig 5.
Shoreline change for the Apollonia (VHR images).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI as obtained from VHR imagery. Quantified LRR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Shoreline proxy is the backshore cliff. A) Full times series: 1949–2019; B) Recent: 2010–2019 and C) Historic to recent: 1949–2010. Basemap: ©Maxar (7/11/2019), provided by European Space Imaging.
Table 3.
Summary DSAS results based on VHR imagery for Apollonia.
Fig 6.
Erosion examples at Apollonia from historic map and VHR imagery.
A) Close-up of the incipient tombolo’s western side and adjacent shoreline (VHR image: ©Maxar [7/11/2019], provided by European Space Imaging). Earlier positions of the eroding backshore scarp are superimposed. Note difference in former scarp positions on the tombolo versus the more stable coastline to the west. B) Excerpt from the Beecheys’ map of Apollonia [6], georeferenced and co-registered to a recent VHR satellite image. Red line marks location of the backshore scarp from the 2019 VHR image. Orange and yellow arrows respectively mark locations where extensive and minor coastal change are suggested by the VHR image–historic map comparison.
Fig 7.
Shoreline change for southwest of Ptolemais (VHR images).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI, or EPR and 90% ECI as obtained from VHR imagery. Quantified LRR or EPR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Shoreline proxy is the waterline. A) Full times series: 1974–2016; B) Recent: 2009–2016 and C) Historic to recent: 1974–2009. Basemap: ©Maxar (25/04/2016), provided by European Space Imaging.
Fig 8.
Shoreline change for Ptolemais headland and to the northeast (VHR images).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI, or EPR and 90% ECI as obtained from VHR imagery. Quantified LRR or EPR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Shoreline proxy is the waterline. A) Full times series: 1974–2016; B) Recent: 2009–2016 and C) Historic to recent: 1974–2009. Basemap: ©Maxar (25/04/2016), provided by European Space Imaging.
Table 4.
Summary DSAS results based on VHR imagery for southwest of Ptolemais headland.
Table 5.
Summary DSAS results based on VHR imagery for Ptolemais headland and to the northeast.
Fig 9.
Examples of coastal change around Ptolemais from VHR images.
For both examples the digitized 2009 backshore cliff/scarp (yellow) and 1974 waterline (red) are superimposed onto the 2016 VHR image (©Maxar (25/04/2016), provided by European Space Imaging). A) Southwest of Ptolemais showing extensive beach and cliffline retreat. Arrow indicates an unnaturally straight cliffline suggestive of human modification. Also shown are possible traces of recent sand mining on the beach. B) Northeast of Ptolemais showing loss of a former spit, recent structures built around the ancient harbour and possible backshore erosion.
Fig 10.
Shoreline change for Tocra (VHR images).
DSAS shoreline change transects classified into statistically significant categories based on LRR and 90% LCI, or EPR and 90% ECI as obtained from VHR imagery. Quantified LRR or EPR (metres/year) is plotted on the inset graph with negative values (red) indicating erosion/retreat and positive values (blue) indicating accretion/advance. Shoreline proxy is the backshore cliff. A) Full times series: 1974–2020; B) Recent: 2010–2020 and C) Historic to recent: 1974–2010. Basemap: ©Maxar (21/03/2020), provided by European Space Imaging.
Table 6.
Summary DSAS results based on VHR imagery for Tocra.
Fig 11.
Shoreline forecasts for Apollonia based on recent LRR from VHR images.
Text shows generalized magnitude of retreat for the backshore cliffline relative to 2019 for different sections of coastline and for 2032 (red) and 2042 (blue). Values only refer to erosion/retreat not advance/accretion: Zones with 0 values show where stability/advance has also been forecast. Values in brackets show the maximum retreat based on the uncertainty bands. Archaeological structures/material forecast to be at risk are annotated. Basemap: ©Maxar (7/11/2019), provided by European Space Imaging.
Fig 12.
Present-day erosion impacts at Apollonia.
A) Erosion of the Roman road (decumanus) in front of the Byzantine installations. B) eroding edge in front of the Byzantine Installations and Roman bath. C) eroding edge in front of the insula. Also indicated is the stretch of backshore where undocumented buildings and mosaics are eroding out. D) Example of a mosaic floor exposed by backshore erosion (photos A and D: 2019, S. Buyadem; photos B and C: 2021, F. El-Gumati).
Fig 13.
Shoreline forecasts for Ptolemais based on recent LRR from VHR images.
A) area southwest and B) northeast of Ptolemais headland. Text shows generalized magnitude of retreat for the backshore cliffline relative to 2019 for different sections of coastline and for 2032 (red) and 2042 (blue). Values only refer to erosion/retreat not advance/accretion: Zones with 0 values show where stability/advance has also been forecast. Values in brackets show the maximum retreat based on the uncertainty bands. Archaeological structures/material forecast to be at risk are also annotated. Basemap: ©Maxar (25/04/2016), provided by European Space Imaging.
Fig 14.
Present-day erosion impacts at and near Ptolemais.
A) Eroding cliffline west of Ptolemais. B) Blocks/structural material eroding out of the cliffline. C) industrial features (warehouses?) exposed by wave action east of the Ptolemais headland. D) Exposed mosaic floors east of the headland (photos A and B 2021: CCS Survey; photos C and D 2022: S. Buyadem).
Fig 15.
Shoreline forecasts for Tocra based on recent LRR from VHR images.
Text shows generalized magnitude of retreat for the backshore cliffline relative to 2019 for different sections of coastline and for 2032 (red) and 2042 (blue). Values only refer to erosion/retreat not advance/accretion: Zones with 0 values show where stability/advance has also been forecast. Values in brackets show the maximum retreat based on the uncertainty bands. Archaeological structures/material forecast to be at risk are also annotated. Basemap: ©Maxar (21/03/2020), provided by European Space Imaging.
Fig 16.
Present-day erosion impacts at Tocra.
A) Roofed cistern documented in 2004; now largely destroyed. B) walls, silo and building, not visible in 2004 and since exposed by coastal erosion. C) Shore-normal walls exposed post-2004 by coastal erosion. D) Part of the defensive perimeter wall, now exposed (all photos: 2022, S. Buyadem).
Fig 17.
Comparison of Tocra in 1974 from KH-9 image with waterlines from the last decade superimposed.
Note the near total loss of the beach in the central part of the site and reduction of the beach in the western part (both indicated by white arrows). Outside these two areas, the remaining waterlines are broadly stable with slight differences resulting from waves/tides at the time of image acquisition. KH-9 image provided by USGS [80].