عنوان مقاله [English]
The coasts are concourse water and land environments that they are influenced from both. The main morphogenesis factors are Include Variety of variables such as geological characteristics, climatic, biological and water sea movements that create Varity of landforms. In this study, has been examined the hydrodynamic processes in land and sea that were affective in the appearance coastline landforms in below of the Jegin River delta in the east harbor Jask. For closer examination, has been emphasized on the formation and evolution processes in coastal bars of Jegin River Delta. Jegin river delta is the largest delta in coastal plain of Western Makran and Hormozgan province. The area spanning latitude 25° 30´ to25° 40´ N and 58° 5´ to58° 30´ E. it has 23.7 km long.
For analysis of Temporal and spatial variations Jegin River has been used Land Sat satellite images, (The MSS sensor in October 1975 with bands 1 to 4, The TM images in June 1987 with bands 1 to 7, The ETM images in April 2001 and May 2005 with bands 1 to 7) and also aerial photographs from 1961 and 1983 has been used.
Gabrik and Yekdar topography maps with 1:50000 scale for base maps and Gabrik geology map with 1:10000 scale for Separation Old Jegin river terraces has been used. The images were processed in ENVI software. And changes in area and dimension of coastal bars have been extracted to timing maps.
For analysis tidal range has been used of daily tides Statistics from 2000 to 2010 in National Cartographic Center. To examine the effects of wind in sand transport direction in surface of coastal bars, Seasonal wind roses in WERPLOT view software has been drawn and their relationships with formation of coastal bars in region has been studied.
Eventually, all of the dates have been transferred on the base maps and have been delineate and adapted in the software ArcGIS and Freehand
Method of study was comparison of changes in coastal bars through a period of 33 years of satellite images and aerial photographs using the above soft wares and field control.
Results and Discussion
Effective variables in formation coastal bars Jegin River are mainly influenced by hydrodynamic processes of the sea (waves, tidal and coastal currents) and Jegin River hydrodynamic in delta surface of land. The erodiblility of Ophiolite complex formation Makran and river flooding are the origin large volumes of sediments transfer to the sea. Sedimentary material is transported by water network and finally, the distribution of sediment along the coastline with interaction other environmental factors lead to the formation of coastal bars.
The waves and tidal currents are the most important marine hydrodynamic processes which in creation of coastline Landforms are distinct than other factors. Deposits are transferred to the coastline by Dora waves and are collided With the Southeast part of delta coast and are distributed along the coastline.
Miles Collision Create the Currents along coastline that Causes sediments move toward the West. Finally function of tidal and coastal currents create by waves, density of silt - sand particles, are formed coastal bars in below of the Jegin River delta.
The results show that significant volume of sediments into coastline by Jegin River is distributed along the coastline toward the west, affected by waves with southwest direction and formed coast bars and tidal lagoon. Time comparison of changes show that the coastal bars been more massive in the eastern part of the coastal delta and changes in area and dimension are function of periodical track change in Jegin river delta firstly and direction of dominant wave secondly. The most change during the period studied is related to the coastal bars in the eastern part of Jegin River delta that it sometimes reaches to 400 meters.