The Effects of Sea Level Fall on the Caspian Sea Shoreline Changes

The Caspian Sea level has experienced frequent fluctuations resulting in shoreline advance and retreat. Therefore, studying and predicting shoreline changes in the Caspian Sea are very important. The "Bruun Rule" was presented in order to predict shoreline variation due to sea level rise. In addition, to improve the predictions of the Bruun rule, added landward sediment transport to it, leading to more desirable results. In this research, the Bruun rule and its modified form, extended for landward transport, were investigated for the Caspian Sea level fall conditions. The modified equation in this study leads to the better results, which indicates that due to sea level fall and natural storms, there would be sediment deposition toward the shoreline. In terms of water level reduction, by applying the coefficient, the root mean squared error was obtained 3.447 meters for predicting shoreline changes in comparison to its natural changes. According to the results, the lowest difference in prediction is related to the Mahmudabad coast and the highest difference in prediction is related to the Dastak coast, which are equal to 0.059 and 4.849 meters, respectively. Based on this trend for forecasting shoreline changes by applying the coefficient and not having much difference in calculating the root mean square error based on the proposed equation of Rosati et al., it is possible to use the optimized equation in this study as a prediction of shoreline changes in terms of sea level fall; This coefficient has improved the forecasting trend of coastline changes in terms of water level reduction for each of the studied areas with direct deviations of D50 and HB in the equation, and the results obtained from forecasting shoreline variations show a lower difference for each area.