مكان الجامعة: بغداد

الصفحات الاولى:

المستخلص: This study deals with the phenomenon of river islands in the course of the Euphrates River between the two cities of Nasiriyah and Qurna within the administrative borders of the provinces of Dhi Qar and Basrah south of Iraq, for about 126.80 Km. The study makes use of geomorphologic applications by using geographic information systems (GIS) to understand and identify natural and human factors that influence the formation and development of river islands and geomorphologic process, in addition to the morphologic and morphometric characteristics of the islands, as well as human activities and future investments in the region. The study depended on the use of GIS programs and special field study by taking soil and water samples and drawing cross - sections by using (Acoustic Doppler Current Profile). The study area tectonically lies within the unstable pavement which is affected by the undersurface tectonic movements. Geologically, the area is covered by quartet time deposits that are new disjoint sediments like the deposits of the floodplain which result from the previous stages activities of the Tigris and Euphrates. They include old sediments which date back to the Holocene and Pleistocene ages. Topographically, the surface of the region is characterized by gradual decline from the north - west to the southeast which set the general direction of the Euphrates River.It has been noticed that there are a number of natural and human factors that play a prominent role in the formation and development of the river islands. However, the impact, contribution and interaction of these factors vary in the formation of this phenomenon. Where the natural factors represented by the geologic structure, the decline, and the characteristics of ancient and current climate, as well as the human factors represented by building dams and reservoirs on the basin of the Euphrates River, in addition to the different uses of the water (agricultural, industrial, domestic) and building bridges and waste harge into the river are all factors that contributed to the formation of river islands within the study area. There is a close relationship between the geomorphologic processes and hydrologic characteristics of the flow of the river as well as the aforementioned factors. The processes that contribute to the formation of the islands vary between being of geomorphologic erosion nature or of sediment nature. This has impacted the classification of the islands according to the affecting process. Erosion islands resultant from the geomorphologic erosion operations lie to the north of the study area. Whereas sediment islands resultant from the sediment operations appear in the middle and southern sections of the study area.The variation of river islands in the study area in their types (permanent, seasonal, joint) and in their morphometric characteristics (dimensions, shapes and areas) is due to the geomorphologic processes that formed them. Visual satellite maps and topographic maps and historic evidence for three periods (1972, 1990, and 2015) were used to interpret the geomorphologic changes within a spatial - temporal framework in the study area. Geomorphologic changes included identifying the location of the islands, their formation, development, transference and disappearance within the consecutive years of the study. The change of the islands and variation in their dimensions is resulted from the balance between the water system and the local geomorphologic environment. Twenty two islands appeared in the course of the Euphrates River between Nasiriyah and Qurna in 1972, and (35) islands in (1990) and (69) islands in (2015). It is noticed that most of the islands developed because of the change in the characteristics of geomorphologic processes from on period to another to reach its peak in 2015 to transfer into permanent islands in a percentage of 45% because of the activity of the sedimentation process. It has been found also that the first thing that the islands do as a natural reaction to their formation is dividing the river into subordinate courses in addition to the main course. Thus, the river appears divergent because of these branches; as a result it is described as braided river or divergent river. The degrees and percentages of the river divergence varied spatially and temporally according to the formation and centering of the islands. It has been found that there is an obvious and higher increase in the degree and percentage of divergence in the southern ourse of the (original Euphrates) than in the northern course. This is due to the fact that the southern course is longer than the northern one in addition to the increase in the centering of the islands in the southern course as a normal result of the increase of length.The study has shown that river operations, which resulted in the formation of geomorphologic shapes, have impacted the present human investments as well as the available potentials. Across its long history, the river contributed in the process of settlement. Its peregrination lead to the change of the locations of some villages and cities on its banks at that time. In addition to its impact on the variation of settlement types along its course. Where, the linear pattern prevails along the course of the Euphrates and its branches in the region.The emergence of river islands also contributed to the existence of a suitable environment for settlement especially in erosion islands in the northern parts of the course. River islands play an effective role on the other activities like agriculture, irrigation, herding and transportation, as well as its impact on tourism activities where they provide many attractive tourism potentials.Moreover, these islands are in the middle of the biggest marshes whether the central marshes or Alhammar marshes adjacent to the study area.