HORIZONTAL DEFORMATIONS OF THE SUKIL RIVERBED WITHIN THE PRE-CARPATHIAN HEIGHT IN 1880-2019

The article presents the results of the study of horizontal riverbed deformations of the Sukil river in the area from the town of Bolekhiv to its confluence with the Svicha river during 1880–2019. The studied section of the riverbed is located within the Precarpathian height and is marked by significant dynamics of the riverbed, which is mainly due to frequent floods, including catastrophic ones. The analysis of long-term horizontal riverbed deformations of the Sukil river and identification of the main factors of their manifestation were carried out in three stages. The first stage involved an assessment of the riverbed displacement over a long-term period of tens of years and was performed based on topographic maps of 1880, 1929-1939, and 1990. The second stage focused on the analysis of the riverbed displacement during a short-term period of 5-7 years and was conducted on the basis of Google Earth satellite images of 2006, 2011, and 2017–2019. The third stage was dedicated to the verification of the obtained results by field research and to the identification of the main reasons for the development of horizontal riverbed deformations. The analysis of historical maps and satellite images was mainly conducted by cartographic methods using ArcGIS 10.1. The riverbed of the Sukil river has significant differences in the development of horizontal deformations on the section of Bolekhiv – the village of Podorozhnie (the mouth of the river). According to the type of manifestation and scale of the riverbed deformations development, two sections (hereinafter dynamic sections) with significant horizontal deformations have been identified: the first one – from Bolekhiv to the village of Lysovychi; the second one – from the village of Lysovychi to the village of Podorozhnie (the Sukil mouth). On dynamic section 1, the horizontal deformations are differently manifested depending on the type of the riverbed. The maximum displacements which were found on the meandering sections are approximately 340 m. They were recorded during the period of 1880–1939. On the sections with a “transitional” type of riverbeds (in the late 19th-early 20th century they were braided, and now they are single channel), the deformations are small (up to 60 m) and are manifested mainly within the boundaries of the riverbed. On dynamic section 2, the Sukil riverbed is meandering and the deformations are much larger. The maximum riverbed displacements reach approximately 500 m (during the period of 1880–1939). For dynamic section 2 as well as for the whole section of the Sukil riverbed from Bolekhiv to the mouth, a certain tendency of the riverbed changes on the plan has been revealed. Thus, from 1889 to 1990 we observe a decrease in the meandering of the riverbed caused by anthropogenic influence, in particular, by the straightening of the riverbed in the 70-80s of the last century and by change in the position of the mouth; since 1990, a natural increase in the Sukil riverbed’s meandering has been observed. Key words: horizontal deformations; riverbed types; Sukil; meandering; historical maps; remote sensing.