Materials and methods

The Kurdan watershed in Alborz province is located between latitudes 35 degrees 55 minutes to 36 degrees 6 minutes north and longitudes 50 degrees 49 minutes to 51 degrees 5 minutes east, its area is 336.5 square meters. The highest elevation is 4059 meters in the northern part of the watershed and the lowest elevation is 1427 meters in the area where the river exits the mountain. Therefore, the height difference between the north and south of the basin is 2632 meters. This height difference has affected the variety of weather and temperature and other geographical features of different parts of this basin.

Watershed is a small part of the sub-basin of the Shur River of Qazvin, related to the Salt Lake basin. The rains of this small watershed are collected by the Kurdan River and directed to the outside. The main branch of this river named Duran originates from the south of Kahar Peak in the rough northeast corner of the Qazvin basin and the neighborhood of the Karaj River watershed.

Analysis of these changes using field evidence and sources such as aerial photos, satellite images, topographic and geological maps, and other physical tools of this research and based on the hierarchical anomaly index (∆a), basin asymmetry index (AF), Branches (R), horizontal topography symmetry index of the basin (T), hypsometric integral (Hi) and drainage pattern of geomorphic parameters have been done. Along with these parameters, by using the research of other researchers and simulating the past climate, it has been tried to analyze the effects of Quaternary climate changes by using the mentioned parameters as modeling and conceptual techniques.

In general, in this research, to detect the active tectonics of the area, it was measured from the topographic maps and aerial photos of the area, and to communicate between the tectonic movements and the drainage network, necessary geological and geomorphic data through the interpretation of geological maps. Topography, aerial photos, satellite images and especially frequent field visits were obtained. In the next stage of this research, evidence of new tectonics in the drainage network of the region has been obtained, and neo-tectonic analysis in the Kurdan basin has been analyzed using analytical-comparative methods and the use of geomorphological techniques. First, the information layers of topographic maps 1:25000 was transferred to the GIS information system in the ArcGIS environment and using it, layers such as drainage network, slope, digital height model were extracted and the results were analyzed using the geological map and according to the values of tectonic indicators. obtained, the morphology of the river in the studied area has been evaluated and analyzed in terms of the amount of new tectonic activity.





Results and discussion

Based on the analysis of morphological parameters and branching index R, considering the branching conditions and the number of these branches, it shows the continuous presence of important tectonic activities in this basin. Also, the high figure of this index fully confirms the high tectonic activity in this basin. In terms of this index, the presence of dense branches in this region shows that it has experienced relatively high tectonic activities. Therefore, the results of this research show that: the studied area has been strongly affected by neo-tectonic activities and climate changes. Based on the obtained results, it shows the high tectonic activity of the drainage network of the Kurdan watershed based on the changes in river morphology and the youth of tectonic activities with high elevations. It can also be said that the documentation of scientific findings has confirmed the modification of morphological forms under the influence of climatic processes.



Conclusion

The results of the morphometric analysis and the analysis of the findings of the studies conducted in this basin show that it has experienced high tectonic activity, and considering the changes in river morphology such as the left deviations, it can be said that this basin from the perspective of tectonic activities It is active and has a young topography despite the high elevations. Also, the climatic evidence in this region confirms that this basin has experienced a sequence of cold/hot and wet/dry periods and has left evidence of glacial periods. Therefore, it can be concluded that the climatic activities in contrast with the tectonic situation of this basin have mainly gradually and at times suddenly and severely affected the basin, and adjustments have been made in the effects of these processes with the activity of climatic parameters. Therefore, the drainage network of the Kurdish basin of this basin is mainly gradually and at times suddenly and strongly affected by tectonics, and due to climatic processes, changes have been made in the forms.



Keyworks: active tectonic, climate changes, drainage basin, Kordan Watershed