Coastal system evolution along the southeastern Caspian Sea coast using satellite image analysis: response to the sea level fall during 1994–2015

The southeastern segment of the Caspian Sea (CS) along the Iranian coast, which has a very gentle inner shelf slope, underwent rapid beach evolution in response to water level changes. Based on satellite altimetry data, the CS basin has experienced an accelerated water level fall drop in recent years, leading to an increase in the rate of shoreline changes. The shoreline dynamics and morphodynamics of the Amirabad coastal zone, Gorgan Bay, Miankaleh Spit, and Gomishan Lagoon are evaluated here to determine morphological changes of the study area. Landsat-TM/ETM+/OLI moderate spatial resolution products were acquired at unequal intervals between 1994 and 2015 to monitor the coastal changes using Geographic Information System (GIS) tools. The Digital Shoreline Analysis System (DSAS), a GIS software extension, has been used for estimation of the shoreline rate of change through several approaches, including End Point Rate (EPR), Linear Regression Rate (LRR), and Weighted Linear Regression (WLR). The results show that both Gorgan Bay and Gomishan Lagoon have significantly decreased in size during recent years, mainly due to the fall of the CS water level. Results also show that water level drop of the CS, along with net eastward littoral transport, resulted in the growing of the Miankaleh Spit. Further analysis based on the wave climate in the southeast CS and net estimated longshore sediment transport indicates that the littoral drift contributed to ~ 6% of the total annual elongation of the Miankaleh Spit during the study period.