Investigating the Effect of Flood Flows on Morphological Changes Using a Series of Satellite Images: Rapid Changes in Morphology of Bazoft River

Abstract

Abstract Morphology is one of the most important branches of river engineering science. Examining the changes in the geometry of sections in rivers that feed large dams is of particular importance. In fact, gaining a better understanding of the river's behavior will reduce potential damages to hydraulic structures and public infrastructure. In this regard, in this research, the morphological changes of Bazoft River, one of the sub-basins of North Karun, which enters the Karun 4 Dam at the end, have been investigated. In this study, using 26 Landsat + ETM and OLI satellite images, the displacement pattern of the main river channel, along with the changes in width and sinuosity resulting from sedimentation and erosion processes in long and short-term intervals leading to the year 2015 and caused by large floods in this period of time was investigated. The results showed that the average displacement of the main channel of the river leading to erosion (sedimentation) for the right and left banks is 14 (15) and 14 (14) percent of the average width of the river, respectively. Also, the net area change rate due to the displacement of the main channel of the river for the right and left banks was obtained as -1.8 and 0.3 hectares per year, respectively. By examining the effect of floods, it was found that the amount of erosion is higher than sedimentation on both coasts, and the left coast is more dynamic than the right coast. The average width of the river in the 30-year period for the four investigated periods is 33.8, 44.7, 40.2, and 38.6 meters, respectively. Also, the width of the Bazoft River did not change much before the biggest flood in 2009 and its value did not exceed 40 meters. But after the flood, the width of the river suddenly increased and these changes seem obvious. The maximum increase in width is related to the second span of the river and its value is equal to 70 meters. Investigations related to four longitudinal intervals along the river's path showed that the sinuosity value in all years in the first interval had an almost constant trend, but in the second and third intervals, its value is higher, so these two intervals are more active than the other two intervals be in the fourth span, which leads to the Karun Dam 4, changes in sinuosity have a downward trend. Also, the results showed that the dewatering of the Karun 4 dam had a significant effect on all the morphological parameters of the Bazoft River in the fourth period. The results of this study perfectly indicated the capability of revealing the river form changes using Satellite Images Time Series (SITS). This homogeneous result indirectly shows that the erosion rate of the upstream basin and the sediment load of the river increased during this period. Therefore, while updating the status of rivers, the effects of protective and structural measures in such rivers can be evaluated in this way and corrected for improvement.