Impact investigation of suspended loads on the morphological changes of Hirmand River, case study: Sistan River

This research was aimed to investigate Hirmand River morphology alterations through the estimation of suspended loads transported by floods. The sediment samples were collected and suspended loads were estimated. The alterations of sediment load along Sistan reach was investigated, spatially and temporally. The suitable reaches for sedimentation inspected through   the high resolution Satellite imageries of Spot-5 (with the spatial resolution of 2.5-5 m). Through the geo-referencing of aerial photos and satellite images in GIS environment, the changes of river width, meander angel, and sinuosity index were estimated during the last 50 years. The t-student test was employed to assess the changes of river width during time. Results showed that the average suspended sediment load of Sistan River was 32 grL-1 and approximately 7.3 million tones sediment load entered to the study reach. According to the results, the river width has been changed, significantly. The river width in 2016 has been decreased by 0.33 of that in 1965 and 73% of the river has no capacity for flow transport and shows a high density of suspended load. This study established that the hydrology parameters (sediment and flood), biologic and slope changes are the main causes of sediment load and the changes of river morphology from a disorganized sinusoidal meanders to limited meanders. During the period  of 1965-2016 the pattern of flow changed from meander to the sinusoidal. The average angel of river from 287.94 changed to 295.26 degree. The average of sinusoidal index changed from 1.39 to 1.18 and the average of flooding bed width from 160.79 m changed to 41.32 m in 2016.