Phys. Geog. Geom. 2026, 49(1): 40–46

https://doi.org/10.17721/phgg.2026.1/131.05

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Dependence of Subbasin Areas and River Valley Widths on Strahler Order: The Prut and Siret Basins

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Olha V. Palanychko, Dmytro I. Igonkin

Yuriy Fedkovych Chernivtsi National University, St. Kotsiubynskoho, 2, Chernivtsi, 58002, Ukraine

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Abstract

The aim of this study is to quantitatively identify the choric and regional levels of river-basin geosystems based on an analysis of the relationships between the Strahler order of the river network, subbasin area, and river valley width, using the Prut and Siret basins within Ukraine as a case study. The relevance of the research is determined by the need to formalize the boundaries between hierarchical levels of basin organization, which have traditionally been defined mainly in qualitative terms.
The methodological basis of the study combines morphometric analysis, GIS modelling, the ALOS PALSAR digital elevation model with a spatial resolution of 12.5 m, and algorithmic processing of spatial data using Python. Subbasins were delineated through the identification of watershed divides, calculation of flow directions using the D-infinity algorithm, and the formation of non-overlapping catchment units. River valley width was assessed by tracing cross-sectional profiles perpendicular to the local channel axis, considering elevation above the channel, the position of watershed divides, and intersections with higher-order rivers.
As a result, 3rd- to 7th-order Strahler subbasins of the Prut and Siret were modelled and their areas were determined. It was established that the distribution of subbasin areas is asymmetric and approximates a lognormal distribution, while the mean subbasin area increases almost exponentially with increasing order. The analysis of river valley width showed a general increase with increasing stream order; however, this relationship is substantially modified by geomorphological conditions. The greatest valley widening is associated with the transition of river systems from mountainous areas to foothill and lowland regions.
The combined analysis of subbasin areas and river valley widths makes it possible to quantitatively characterize the transition from the choric to the regional level of river-basin organization. Subbasin area reflects the horizontal scale of the catchment, whereas valley width characterizes the morphological expression of the valley structure. Together, these indicators may be used as complementary criteria for analyzing the hierarchical structure of river-basin geosystems and for comparative geomorphological studies.

Keywords

GIS modelling, river valley, river-basin system, choric level, regional level.

Received: May 15, 2026 / Accepted: June 10, 2026 / Published online: June 14, 2026