عنوان مقاله [English]
The position of the coastline depends on interactions between waves, tides, rivers, storms, geological structures and physical processes .Recognizing the spatial variations of the coastline, one can understand the dynamics of coastal zones and morphodynamic processes It is absolutely necessary to manage shore line changes.
The Caspian Sea has created a unique environment with special characteristics due to frequent fluctuations and periodic changes, such as in closed lake environments. Due to this change in the level of the water base, we see large changes in the coastline in the coastal areas of the Caspian Sea. The sea shows a decrease of about 3 meters in the 48-year period (1929-1977) and has experienced an increase of about 3 meters in a period of 18 years (1995-1997). Given the awareness of the changes in the Caspian Sea, we need a method that clearly shows these changes in time and place. The purpose of this research is to investigate the 60-year variation of coastal lines using remote sensing data in the Caspian region.
The research method was descriptive-analytic based on remote sensing data and aerial photographs using the GIS. The aerial photographs of 1956 and Landsat satellite images were used in 1994, 1976, and 2017. These images and images were originally prepared in Envi5.3. ArcGIS 10.5 ArcGIS 10.5 transcoded transects and their statistical calculations. The statistical methods used in this study to determine the coastline variation in the DSAS plug-in are End-End Rate Method (EPR) and Linear Regression Rate (LRR).
Results and discussion
In this paper, maps and diagrams required for analysis have been extracted based on the drawing of coastlines and calculations in the DSAS plug-in. From this, one can assess and analyze how the 60-year change process was taking place in the study area.In the study area, by plotting the base line and transects 50 meters apart, the maximum, the lowest and the average changes during the time period are calculated. The map of variations in two methods shows the amount of variation along the coastline. In this study, the coastline coastal speed and coastline rate for the Haraz delta range is -0.15 m and for Babolrood range is +0.05 m and Talar range is +/16 + m.In these maps, the variation in estrus varies from one side to another. In the Bablrood Delta, the seaward section has advanced to the sea, and in the Haraz and Talar deltas, this is reversed. In the EPR method, as we can see, erosion occurred in the Haraz delta around the estuary of the river, and as much as the river estuary refers to both sides of the east and west, we see a replacement of sediment instead of erosion. In the Bablrood Delta, there is almost a picture of the Haraz Delta, but Talar River delta conditions are slightly similar to those of the Haraz, with variations in the Haraz Delta quite typical. In the LRR output map, the results are similar to those of the EPR method, with the exception that the erosion intensity in the Talar River is less than that of Talar. Because the LRR method uses all coastlines drawn for computation, the result of this map can be more accurate.
In this research, using transects method, the statistical characteristics of coastline changes during the 60-year period have been studied. According to the results of the maps, the general trend of erosion in the studied area is toward coastal erosion. Depending on the basis of the LRR method, the largest changes in the delta of the Babolrood River are observed at 5.9 m, while the adjacent delta of this quantity does not reach 2m. This difference indicates a remarkable sea in the Babolrood Delta, which can be considered a human factor especially in recent years, among the most important reasons. But comparing the results between the maximum and minimum changes, as shown in Table 3, shows a high degree of variation in these three delta. The result of the use of DSAS outbound maps is an important consideration and that in spatial analysis, the use of such single-dimensional Negri instrument will be transformed into a multi-dimensional view, and in this study we observed that during a coastline interval, 60-year-old change can be quite a photo.