Bystrytsia River morphodynamics in the Precarpathian Upland since 147 years ago

Abstract

The article describes the modern morphodynamics of a small river in the foothills. The Bystrytsia (Tysmenyts’ka) River in the Precarpathian Uplands was chosen for the research. It has typical riverbeds: single-channel, multi-channel and meandering. The morphodynamics of the riverbed was studied using the maps of different times (1877, 1906, 1940, 1959) from the different resources ("Archival maps of Poland and Europe"; 1989 from the collections of the Faculty of Geography; 2023 from the resource Open Street Maps; Space images from 2005, 2010, 2014, 2019 and 2021 from the resource Google Earth; 1989 and 2024 from the resource EO Browser). Five sections of the riverbed were identified, where the morphodynamics manifested themselves differently depending on the morphological type of the riverbed and the width of the floodplain. The first section had the following change: two- and multi-channel straight (1877) → single-channel slightly sinuous (1906–1940) → multi-channel straight (1989) → single-channel slightly sinuous and meandering (2021–2024). The second section showed the following morphodynamics at different times: multi-channel sinuous riverbed (1877) → two-channel slightly sinuous with a fragment of a multi-channel (1906–1940) → single-channel slightly sinuous with old riverbeds (1989) → single- and two-channel slightly sinuous (2021–2024). The third segment is characterized by morphodynamics: multi-channel straight (1877–1940) → single-channel straight channel (1989) → single-channel slightly winding with a meander (2021–2024). The morphodynamics of the meandering type of channel in the fourth and fifth segments manifested themselves in changes in their shapes, sizes, angles of turn, deflection length, and transformation of small meanders of the channel. According to the results of the research, we observe a pattern when periods with sufficient precipitation prevailed in the late 19th and early 20th centuries, the channel morphology had mostly a multi-channel or two-channel form. In the middle and late 20th century the structure is simplified - the channel becomes mostly a single-channel straight. At the beginning of the second decade of the 21st century, the single channel acquires bends and meanders, which was not characteristic for any of the periods. With more precipitation, the water runoff of the river increases and, accordingly, the river bed becomes multi-channel and meandering. In the third decade of the 21st century, the river takes on a straight shape and a single-channel, rarely – two-channel bed prevails. Extreme floods change the morphology of the channel, and in the periods between them, the river has a stable shape and accumulates potential for changes.

Key words: river morphodynamics; river channel; horizontal deformations; instability; modern fluvial processes; channel dynamics; river Bystrytsia; Precarpathian Upland.