Shoreline changes at Gomishan Lagoon in light of Caspian Sea’s water level fluctuations

The shifting of coastlines under the influence of hydrodynamic factors and the increase in sea level have caused serious damage to economic, social, and environmental infrastructure, and the rapid fluctuations in the Caspian Sea water level since the 20th century have created unfavorable conditions for the environment of coastal areas . The main objective was to assess the severity of changes in the shores of Gomishan Lagoon during a period coinciding with the decrease in the Caspian Sea water level during the years 1995–2019. Morphological conditions were investigated using field observations and satellite image analysis. The intensity of coastline displacement was calculated by processing multi–time belonging to the years (1995–2019) GIS environment and using Digital Shoreline Analysis System (DSAS). Based on shoreline movement, the study area was classified into three groups according to shoreline changes (high, medium, and low). The results show that the northern extremities of Gomishan Lagoon have the highest amount of shoreline displacement and the amount of shoreline displacement gradually decreases in the central and southern areas.## The only exception is the negative movement of the shoreline, overlooking the mouth of Gorganrud River, which has retreated landward by 150 cm in 24 years, to 878 m. The average annual displacement of the coastline in the study area was 195 m, with maximum and minimum displacements of 344 m and –37 m, respectively. Additionally, the coastline retreats approximately 50 m each year at the mouth of Gorgan River.