Due to the changes and transformations caused by natural and man-made factors that occur in the catchment area and along the course of the river, the flow pattern is constantly changing. It is obvious that knowing the phenomena and the effects caused by their changes on the flow conditions can play an effective role in minimizing the damages and problems caused by floods as well as the optimal exploitation of the river. In the Qashlaq basin, the development of agricultural and garden lands in the borderlands of the river in the past three decades has caused an increase in the density of uses around the river and more pressure on this water source. For this purpose, in this research, firstly, by using satellite images of Landsat 8 sensor OLI/TRIS and Landsat 5 sensor TM in the Google Earth Engine system with a spatial resolution of 30 meters and random forest classification method, land use for the years 1990, 2000, 2010 and 2020 were prepared and the changes made in each period were analyzed. The biggest changes are related to the third period, i.e. 2010-2020, where residential use has increased by 23.3%, rainfed agriculture by 57%, and irrigated agriculture by 52.7%. while pastures decreased by 16.9 percent. The land use changes were also investigated in the bed, boundary and transverse extent of the river, and the results showed an increase in the area of residential areas and expansion of occupations in different periods by 154.1% in the period of 1990-2000, 60% in the period of 2010. - 2000 and 31.3% in the period of 2010-2020 was in the bed of Gheshlagh river, in this regard, necessary measures should be taken to remove the occupations and reopen. Then, according to the rainfall intensity at the time of concentration of the study sub-basins and the different return periods, as well as the CN values extracted from the combination of land use maps and soil hydrological group maps, and the peak discharge of the basin in the year Studies were determined in the HEC-HMS software environment. The results show that the peak flood discharge has been increasing over time. The biggest changes in the percentage of discharge peak are related to the third period (2010-2020), which due to the decrease in pasture use and the increase in agricultural and residential uses, the potential of runoff production and finally CN has increased, and this has caused an increase in the peak discharge of the basin. |