عنوان مقاله [English]
Background and objectives: The study of changes in the behavior of rivers is of particular importance in the protection of aquifers and the determination of the boundaries of the river bed, as well as the reduction of possible damages. Dams are among the structures that have the greatest impact on river morphology. Therefore, it is very important to study the morphology of rivers leading to large dams in planning and ease of strategic decision making on the construction of engineering structures along the river. In recent years, due to the unique characteristics of remote sensing and satellite images, many studies have been done to investigate the morphological changes of rivers. In this research, the study uses 26 Landsat satellite images to investigate the morphological changes of the Bazoft River in a long time period between 1985 and 2015.
Materials and Methods: In order to evaluate the morphology of a river, determination of the morphological parameters such as river boundary displacement, changes in the area caused by erosion and accretion of the banks in the long and short periods is essential. It should be noted that the short and long term periods were 1 and 10 years, respectively. To determine the required satellite image data, 26 frames of Landsat satellite images were selected and analyzed using ENVI and GIS softwares. Finally, the map of the studied river boundary was prepared and difference between the main channel of the river on the left and right bank on the cross section in two different years was considered as the main channel movement in that time interval. The negative and positive values of the main channel movement show accretion(land development) and erosion (land degradation), respectively.
Results: The results showed that the most changes occurred in the 62 to 84 km range of Bazoft River, which is due to the presence(existence) of riffles near the Mavarz hydrometric station and numerous lateral branches in these two intervals. Investigation the area of erosion and accretion in long-term periods showed that in the years 1985-1994, 1994-2005 and 2005-2015, the river was associated with coastal accretion. For the 30-year period of 1985-2015, the average accretion and erosion of the river was estimated to be about 69.43 and 42.34 hectare, respectively. Due to accretion about 27.09 hectare of new land has been created in the studied period time. In the short run, the results showed that there is no significant difference between the mean accretion and erosion of the left bank, and on this bank the accretion area is about 2% more than erosion, whereas on the right bank of accretion, there were about 8 % of the erosion that this difference is meaningful at 95 %.
Conclusion: Investigation of the morphological changes of Bazoft River using satellite images in a thirty-year period showed that the most changes are in the range of 62 to 84 kilometers of the river, which it can be considered for the river management planing such as river protecting. The most accretion area was observed near the Mavarz hydrometric station and adjacent to Khuzestan-Chahar Mahal and Bakhtiari road so it can be proposed as a suitable place for sand and gravel harvesting as a nonstructural method for river protection. Generally, the left bank was more prone to erosion, while the amount of accretion in the right bank is greater than the erosion.