Hundreds of satellite images spanning over 25 years have been compiled to show the evolution of Greece’s ever-changing coastlines.
For decades, coastal areas have been subject to intense urbanisation and population growth. These areas are some of the most dynamic on Earth and, unfortunately, suffer from severe coastal hazards owing to storm activity and sea level rise. Monitoring coastal areas is key to understanding the evolution of coastal dynamics and in helping authorities protect these environments.
The Space for Shore project, funded by ESA, provides a variety of tools for coastal erosion monitoring using Earth observation products. The consortium is composed of technical experts from five European countries.
The results highlight the fragility of Greece’s coastline and indicate the likelihood of coastal erosion increasing in the coming years. Over the 1995—2020 period, around 40% of the coastlines analysed have shown ‘progradation’ which is the seaward growth of beaches caused by the progressive build-up of sediment. The team found that nearly 10% of the studied coastal areas are subject to erosion greater than 3 m per year.
Deltas, estuaries and capes appear to be the most exposed areas with retreat that can reach 30 m per year. Erosion at river mouths are especially of great concern as this signifies a sediment deficit and suggests critical and long-lasting consequences for coasts deprived of sediment input from rivers.
The high-frequency monitoring of nearshore bathymetry is key in sediment management and coastal engineering. The analysis shows that changes in the nearshore bottom slope, sandbar migration or even an overall increase in depth, are all worrying signs of sediment shortage that can forewarn or aggravate coastal erosion.
As an example, the team studied Zakynthos Island, particularly the Laganas coastal area. Given that the beaches are frequently watched by ecologists who closely monitor the migration of loggerhead sea turtles, they found it to crucial to observe the bathymetry and the waterline of the coast to record changes in its environmental impact.
Aurélie Dehouck, Head of i-Sea and coordinator of Space for Shore, commented, “Over the last 25 years, our analysis has revealed a strong variability in Greece’s coastlines, with extremely dynamic local changes.
“Through the Space for Shore project, a comprehensive set of in situ scientific measurements, combined with numerous retrospective remote sensing data were produced. Thus, an evidence-based up-to-date assessment framework for the extent of coastal erosion was provided, rendering it an extremely helpful and substantially incomparable toolkit to the coastal managers throughout the region, both for the present and future use,” commented Athanasios Nalmpantis from the Public Sector at the Region of Eastern Macedonia & Thrace.
On 22 January, the results of the Coastal Change from Space project were presented in an online webinar.
SCIENCE project was attended on 29th April 2021 with a vPiCO presentation to the NH6.8 session: Remote Sensing & Cultural Heritage of EGU General Assembly 2021 (19-30 April 2021).
Moreover, the SCIENCE project presentation was cited as follows: Tompolidi A.-M., Parcharidis I., Loupasakis C., Fragiadakis M., Soupios P., Grigorakou E., Achmet Z., Kalousi G., Eleftheriou V., Michalopoulou D., Christodoulopoulou R., Kanaki E., Mavromati D., Sythiakaki V., Elias P., and Gatsios T.: SpaCeborne SAR Interferometry as a Noninvasive tool to assess the vulnerability over Cultural hEritage sites (SCIENCE), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13397, https://doi.org/10.5194/egusphere-egu21-13397, 2021.
Also, supplementary material of the primary interferometric results of the SCIENCE project was uploaded on the virtual EGU platform and will be available until 31 May 2021 to all the participants of the symposium.
CASE STUDY: HERAKLION CITY WALLS IN CRETE, GREECE
Ιn the framework of the Heraklion City Walls case study (Fig.1) a variety of Persistent and Distributed Scatterers are combined aiming to produce highly accurate deformation maps (Persistent Scatterers & Distributed Scatterers Interferometry – PS/DS-InSAR) for predicting the vulnerability of the Venetian city walls to ground deformation in time and space.
The dataset that has been utilised is consisted of 175 Single Look Complex (SLC) images acquired by the Copernicus Sentinel-1A & B satellites in descending orbit for the time period from October 2014 to September 2020
For further information click here .
Watching out large-scale waterline and coastal changes in Greece
Terraspatium backed by i-Sea has processed hundreds of satellite images over the 1995-2020 period of time to perform the very first dataset describing the location and evolution of shoreline over time in Greece, which has been then turned into a preliminary coastal erosion assessment at the scale of the Peloponese, Eastern Macedonia and Thrace regions.
In Greece, as in every coastal mediterranean regions and similar enclosed seas where the tidal range is low, coastal erosion can be monitored by focusing on waterline temporal variations during low-energy wave conditions. Optical satellite archives (Landsat, Spot, Sentinel-2) have been processed using supervised classification algorithms to extract land/sea interface in a semi-automated user-controlled and robust way ensuring readiness for large database processing and method replicability at regional and national scales.
Changes in the waterline position are usually computed and estimated along regularly spaced profiles perpendicular to the coast highlighting hot spots of shoreline retreat which experience strong coastal dynamics or being particularly vulnerable to coastal erosion hazard.
A first demonstration of satellite-derived bathymetry has been made in Greece, here is an example obtained at Laganas Island, where the underwater topography has been retrieved up to depths of 30 m. This opens door to systematic monitoring of shallow water bathymetry changes over sandy areas suffering from coastal erosion and in complement to beach and shoreline monitoring with the overall objective of achieving a better understanding of coastal dynamics and sediment budgets.
From large-scale decadal variations in shoreline to yearly and storm impact assessment
Directly derived from satellite-based waterline time series, variations in shoreline position may be computed at every required time scale, as here along the Northern Peloponese coast where shoreline evolution was computed on a 5-year basis. The same has been done in other European regions at higher frequency (monthly) enabling catching storm impact and beach natural recovery in the months following storm events.
The results obtained during the project lifetime #25-year of shoreline change over more than 900 kms of coastline# testify how mature is the Space for Shore coastal erosion service and ready to play an active role in the future coastal monitoring infrastructure the Greek authorities has been thinking about…
“Through the Space for Shore project, a comprehensive set of in situ scientific measurements, combined with numerous retrospective remote sensing data were produced. Thus, an evidence-based up to date assessment framework for the extent of coastal erosion was provided, rendering it an extremely helpful and substantially incomparable toolkit to the coastal managers throughout the Region, both for present and future use.”
A. Nalmpantis (Region of Eastern Macedonia & Thrace)
“Outstanding first try, you set up the road for the coastal monitoring in Greece”.
Dr. T. Papadopoulos (Peloponnese Technology and Innovation Centre)
Years analysed : 25
Km monitored : >900
Sites of interest : 09
Products : 385
Here you can find the full Greek Case Study of Space for Shore project.