Shoreline changes at Fereydounkenar Port in light of Caspian Sea’s water level fluctuations

Abstract

Water level fluctuations of the seas have long been recognized as one of the driving factors influencing the shoreline position. In comparison with open seas, due to some distinctive features, the Caspian Sea (the largest inland sea on the earth) experiences broader water level variations in a relatively shorter time span. Revealed by analyses within this study, shorelines around Fereydounkenar Port (located on the southern coast of the Caspian Sea) shift significantly in response to the Caspian’s water level fluctuations. Accordingly, this research is focused on addressing the impacts of these fluctuations in studying shoreline changes that surround this port. In this regard, historic shoreline positions were extracted from 1983, 1994, and 2004 aerial photos as well as 2013, 2014, 2016, and 2018 satellite images. The mentioned shorelines were georeferenced and digitized manually. To enhance the accuracy, for each shoreline position, the uncertainty values of georeferencing (Ug; equal to RMS error of georeferencing), digitizing (Ud; 1 m according to the dry–wet index), and proxy-datum bias (Upd; to address the seasonal effect) were measured and considered in the calculations. Calculations of shoreline rates of change were carried out by the Digital Shoreline Analysis System (DSAS) tool on the ESRI ArcGIS software package. Two separate scenarios for increases and decreases in the water level were established to calculate the rates of change for each water level condition. Finally, based on calculated change rates and by assigning some modification factors (according to the water level on a specific date), shoreline positions can be modeled for any given date—which considers both the sedimentary budgets of the area and the impacts of the water level fluctuations. Verification of the hindcasted shorelines also showed that in six out of eight divisions, the average differences between the hindcasted and the actual shoreline position were desirably within the calculated uncertainty range; which was 4.85 m to 5.9 m.