عنوان مقاله [English]
The coast is a dynamic environment continually adjusts to the effects of weather, tides, seasons and climate change. The coastal area cannot withstand too much misuse it is inherently unstable and liable to change. Rapid changes in coastlines and morphological aspects an important feature of these areas, particularly around ports and other structures are manmade. Protection of ocean and marine coastal regions is a vital part in any coastal management program for sustainable development. The coastline is the most dynamic aspects of the Earth's surface. Thus, mapping the coastline and the changes it is very necessary for planning and efficient use of the beaches. On the other hand, in our modern world, coastal engineering sciences and assessment of coastal sediments and erosion are considered to be vital elements in management of national coastal areas. A large part of sediments of Caspian Sea coast are subject to erosion as a result of environmental forces (fluctuations in sea level and coastal waves and currents as well as wind). The rate and severity of erosion hazards varies depending on the morphological and geography and hydrodynamic properties of coastal areas. The case study in this research is situated at coordinates of geographical longitude from 53ْ, 10َ, and 00ً up to east 53ْ, 24َ and 00ً and geographical latitude 36ْ, 47َ, and 00ً up to north 36ْ, 52َ, and 00ً the southeast coasts of the Caspian Sea on the ports of Amirabad and Neka in the East of Mazandaran Province.
Change detection helps in ascertaining shoreline trend analysis and its future prediction.The main purpose of this research is assessment of coastline changes in the south east coasts of the Caspian Sea during 1987-2015. Thus, satellite imagery (Landsat 5, 7 and 8, TM sensor for June 1987 with bands 1 to 4, ETM+ [Landsat 7] for July 2001 with bands 1 to 8 and ETM [Landsat 8] for August 2015 with bands 1 to 11), topographic maps (with scale: 1:50000 and 1:250000) and geographical information system software in Arc GIS 10 and Erdas Imagine 9.1 software, have been used. The use of satellite images is an effective technique for study and assessment the occurred changes in the coastal zone. So, in this study, in order to monitoring changes in the coastline, Landsat satellite images (TM and ETM+ Sensors) for 1987, 2001 and 2015 have been used. In order to determine the amount of change in the coastline in the study area, the best band combination and one band was chosen to extract the shoreline. Then, the change and move coastline on the images of 1987 and 2001 and 2015 in eight points and was measured by observing the distance of 2000 m. Then, the amount of sedimentation and erosion in the area were also calculated.
Result and Discussion
The results indicated who the coastline during the period under review, from 1987 to 2001 and from 2001 to 2015 is progress to the sea in the most parts and only in the eastern ports of Amirabad and Neka eroded. The greatest amount of progress and retreat of the shoreline of the years 2001-1987, respectively, are 450 and 68 m. While these values during 2015-2001, respectively 311 and 112 m has been. Also, the rate of sedimentation and erosion in the area of 1987-2015 respectively has been about 5.69 and 0.53 square kilometers.
The results of this research show that most of the changes occurred in the study area in the period 2001-2015. Analyzing satellite images of the study area show that due to the construction and development of the ports of Amir Abad and Sadra drastically changed, so that the coastline in most parts toward of the sea progressed and main phenomenon in the study area has been sedimentation. The interpretation of satellite image data indicates that areas at opposite sides of the Amir Abad and Neka ports had different responses to depositional and erosion processes. Beach modification impacts have aggressively developed at the central part of study area groynes at the Amir Abad port have caused sediment accretion at the west side but erosion processes could develop as the beach retreats on the east side. The maximum progress amount in coastline of the study area is occured in the western part of Amir Abad port during the period 2001-1987, which at 450 meters has been changed. Also, the results show that significant volume of the sedimentation is deposit in west section of the Amir Abad and Neka ports. But, east section of these ports is faced with erosion. Moreover, the most change during the period time studied is related with volume sedimentation in the western section of Amir Abad and Neka ports that it somewhere reaches to 130 hectare. The results of this research can be applied in development plans for engineers and issues in the integrated coastal zone management for study area.