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Gorgan Bay is considered a geological landscape and a coastal sedimentary environment in the southeast of the Caspian Sea. The hydrodynamics of the coasts of this region is subject to the general hydrodynamics of the Caspian Sea. Due to the low slope topography of these beaches, the slightest change in the sea level will lead to hundreds of meters from place to place in the coastline of this area. Changes in the water level of the Caspian Sea is an environmental and coastal management problem, and today the decreasing trend of the water level of the Caspian Sea during the last few decades has caused destructive effects such as land formation on the coasts of Gorgan Bay. In order to investigate the effect of changes in the level of the Caspian Sea on the southern shores of Gorgan Bay in a period of 66 years, existing reports and studies have been used and field surveys have been used, and the coastlines of the studied area have been monitored through the processing of aerial photos from 1955 and Landsat satellite images. MSS, TM, ETM and +ETM have been carried out in the years 1975-2021 in Arc GIS and ENVI software. Coastal changes were processed during 4 periods. During this period, the level of the Caspian Sea water level fluctuated between -26.5 and -28.7 . Based on the results obtained from satellite images and field visits of Gorgan Bay, 1 stage of water level increase in the period of 1995-1985 by the amount of 131 square kilometers and 3 stages of water level decrease in the years 1955, 1985-1975 and 2021-1995 by the amount of It has covered 246 square kilometers.

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Soil erosion in watersheds, causing problems such as the loss of agricultural land productivity and reduce soil surface layer, endangering the life of reservoirs and water utilities, loss of soil fertility, increasing flood, threatening human food security, etc. The negative effects of soil erosion, watershed management operations to improve care. According to the extent of the watershed and the lack of resources, prioritizing catchment areas due to the urgent need to implement watershed management plan is one of the solutions. Therefore, in this study the hydrological response units (HRU) were extracted in the Latyan dam basin. Hydrologic response units as a new approach can form smallest catchment study area. The need to prioritize the hydrological response of the watershed, using "Simple Additive Weighting and weighing "Analytical Network Process were performed. The results show that Most amount of erosion and Following the First Priority of Watershed's preserve is in the eastern part of the lake dam And the upstream basin with poor ranch land use, sedimentary-alluvial lithology and 26 degree of slop.