Estimating the Peak Discharge and Analyzing the Hydrological Changes of the River Case Study: The Mountainous Section of the Qaranqoo Chay River

Knowing the maximum flow rate is necessary to deal with floods, and one of the main problems in watershed planning is the lack or absence of necessary statistics, especially hydrological statistics. Therefore, the absence or lack of hydrometric information in watersheds requires appropriate experimental methods to estimate the maximum discharge. Thus, this research aims to estimate the maximum discharge in the mountainous part of Qaranqoo Chay and analyze the hydrological changes of the river. This research relies on fieldwork, using satellite images and topographic and geological maps. In this research, the water velocity was first measured using the Costa and Jarrett method, and then the flood discharge was estimated based on that. The hydrological conditions of the river were also calculated according to the data of the upstream and downstream stations of the range and using 18 indicators. The research results show that the maximum flood estimated by the Costa method (89.60 m3/s) is closer to the observed values, which indicates the efficiency of this method. Based on the research findings, the connection of Saraskandchay, Shorchay, and Khatonabadchay branches, high slope and impervious formations, low cross-section and channelization of the flow, local blockage due to the fall of large stone fragments and the filling of the section can be considered as the reason for the high maximum flood values in the mountainous part of Qaranqoo Chay. In addition, the results of the study showed that the construction of the Sahand dam caused a fundamental change in the downstream flow regime, and these changes affected the hydrological characteristics.