Morphometric Analysis of the Numrug River Basin in Eastern Mongolia

The Numrug River basin is situated in the eastern part of Khalkhgol soum, Dornod Province, extending across the border into China. Topographically, the basin is relatively elevated compared to its surrounding areas, and Cenozoic-aged basalt formations are distributed throughout the region. This study applies morphometric analysis to characterize the morphological features of the Numrug River basin. Utilizing Geographic Information Systems (GIS) and Digital Elevation Model (DEM) data, geometric, linear, areal, relief, and morphotectonic indices of the basin were identified. The total area of the Numrug River basin is 4,356.68 km², with a basin length of 100.62 km, a width of 43.30 km, and a perimeter measuring 540.51 km. The basin comprises 1,040 first-order, 218 second-order, 52 third-order, 14 fourth-order, 4 fifth-order, and 1 sixth-order stream segments. The cumulative stream length is 3,117.06 km, distributed by order as follows: first-order – 1,594.26 km; second-order – 733.41 km; third-order – 397.90 km; fourth-order – 180.63 km; fifth-order – 108.46 km; and sixth-order – 102.40 km. The basin exhibits relatively low drainage density, pronounced surface dissection, and high infiltration and percolation rates, resulting in limited surface runoff. Regarding slope characteristics, most of the basin features gentle to moderate slopes. Morphotectonic analysis indicates a westward tilting of the basin, while hypsometric analysis suggests that the river is at a mature geomorphic development stage. The basin’s shape and associated morphotectonic indices imply a moderate degree of tectonic activity. In the future, this methodology will be used for tectonic geomorphological analyses of major rivers and streams in Mongolia, contributing to a deeper understanding of land surface evolution and development patterns.