Assessment of the changes in shoreline using digital shoreline analysis system: a case study of Kızılırmak Delta in northern Turkey from 1951 to 2017

Abstract

Dams, which indeed have many benefits, are hydraulic structures that retain sediments in the rivers on which they are built. This property of dams can cause hydrological and geomorphological alterations in parts of the river beneath these structures. Among the three largest coastal valleys of the Anatolian Peninsula, Kizilirmak Delta suffers from geomorphological changes as a result of large dams being constructed there. Sediment is retained in the dam reservoir, which results in a considerable decline in the total amount of sediment that reaches the Kizilirmak Delta. When Altinkaya and Derbent Dams were constructed within the vicinity of the delta, sediment input nearly stopped. The most affected part of the delta was a 4 km stretch of shoreline and a coastal strip situated at the east of the river mouth. The aim of our study was to determine the erosion rates and the shoreline changes in the delta between the oldest available date (1951) before construction of the large-scale dams on the Kizilirmak River and the latest data (2017). To compute the net shoreline changes and erosion rates over these 66 years, we used geographic information system software. This 4-km stretch of shoreline at the east of the river mouth was investigated as two subdivisions. The study timeframe was divided into subperiods to uncover the impacts of the dams over time, and the net shoreline changes were calculated for each subperiod. According to the net shoreline computations for Subregion I, the delta retreated by 604.85 m. In Subregion II, the delta shoreline advanced by an average of 231.68 m until 1990, but it retreated by an average of 409.05 m between 1990 and 2017. According to the linear regression rate (LRR) analysis, the calculated erosion rate in Subregion I is − 11.46 m/year, and in Subregion II is 6.10 m/year for the period between 1951 and 1990 and − 15.10 m/year for the period between 1990 and 2017. When the results of net shoreline movement (NSM), LRR, and end point rate (EPR) were considered together over different time periods, it was clear that dams, which were constructed within the vicinity of the delta, were increasing the retreat in delta shoreline.