Long-term spatial and temporal shoreline changes of the Evinos River delta, Gulf of Patras, Western Greece

This study deals with the long-term shoreline displacement of the Evinos River delta in Western Greece using various geospatial data sets from different sources. The comparison between the extracted coastlines allowed us to identify segments where the delta progrades and parts of the delta that are being eroded over the periods 1945-1969 and 1969-2015. Coastal area variations giving land losses or gains of the most active sectors of the delta associated with changes in shoreline position were calculated over the periods 1993-2002 and 2002-2018 using Landsat TM satellite images. The results showed that nearly 46% of the Evinos delta is in retreat. Erosion is essentially affecting the eastern deltaic shoreline with retreat rates commonly reaching up to 8 m/yr in places. In addition, the area of the artificially closed pre-1959 mouth of the river has retreated at an average rate of 14 m/yr over the past 57 years. The old natural mouth of the river (depicted in a map of 1885) at Akra Evinou (Cape Evinos) has retreated up to 350 m (5 m/yr) over the last 71 years. West of the active river mouth, mobile elongated features such as sand spits and barriers are formed by deposition of sediment produced by the erosion of the abandoned eastern delta coastline. The main natural cause of the long-term Evinos River delta coastline displacements is the nearshore current activity induced by the dominant incoming wind generated waves. Land loss of the active part of the delta (at rates up to 16,797 m2/yr) has been recorded over the period 2002-2018. This generalized erosion can be attributed to human activities that include: the construction of a dam in the upper reaches of the catchment that dramatically decreased the suspended sediment concentrations in the delta, the extensive sand and gravel mining in the distributary channel, and a small earth dam constructed at the apex of the delta for irrigation purposes.