Monitoring of horizontal displacements of the Prut River bed using geoinformation technologies

Abstract

River beds are one of the most dynamic geographical features on the surface of the earth, accompanied by constant movements and displacements. They respond well to the dynamics of temperature and climatic conditions, changes and variability of meteorological conditions, as well as human load. Increasing rainfall during the season, the recurrence of abnormal seasons lead not only to an increase in the water level in the channel, but also to an increase in both the number and width of the river's hoses, contributes to the change of the location of the main channel, accompanied by watering old women and floodplains, the accumulation of sediment and the increase of washouts. Horizontal displacements of the channel significantly affect the cultural and natural landscapes and human economic activity. Conversely, human activity, in particular, mining and large-scale hydrotechnical works in the valleys, also change their course. Insufficient study and research of riverbed issues can lead to the flooding of large areas, which is particularly dangerous for settlements. The current insufficient number of existing hydrological posts, the reduction of field research opportunities, the deterioration of the quality and the inaccessibility of hydrometeorological, mapping information, and for most water bodies simply the lack of data leads to the impossibility of a comprehensive hydrological and morphological study of the river basin and the assessment of intensities. For this reason, in most of the works encountered and related to similar issues, a small local body of water or a section of the main channel or its tributary is selected for research. An important problem is also the comparison of the morphometric characteristics of the river network on topographic maps and plans of different scale series. The river meandering close to reality can only be displayed on large-scale maps. The smaller the scale of the map, the more straightened or generalized the drawing of the rivers. Therefore, it is advisable to carry out such assessments and study of horizontal displacements of the channel on the cartographic material of one scale series. The horizontal displacements of the Prut River bed within the city of Chernivtsi were investigated using topographic maps and plans of different scale, for more than 160 years of observations. About 15 km of the Prut River bed has been digitized. For a better and more detailed analysis of the change in horizontal displacements of the riverbed, the study area was divided into three sections - West, Central, and East. The choice of a place of division is caused by features of the winding channel. The search of maps of different scales in previous years for this territory made it possible to compare the horizontal displacements of the Prut River bed both in time and in space. Topographic maps of 1: 100000 scale in 1982, 1:50000 - 1940 and 1977 and 1:25000 of 1947 and 1957, maps of the Austrian monarchy of 1:75000 - 1855 were found. Analysis of the spatial-temporal changes of horizontal displacements of the Prut River bed by space images and topographic maps during the 161-year observation period showed significant differences in terms of the most meandering channel and its size and shape. Using time analysis, it was found that the highest meandering of the channel was observed in the middle of the twentieth century and amounted to 1.33 and decreased to 1.12 as of 2016. Virtually unchanged, in terms of horizontal displacements, the channel remained in the central part of the study area. In the eastern and western parts, the tortuosity coefficient is increased due to the meandering of the channel and due to the presence of the sleeves, especially in the Kalichanka area. For the western part, the greatest changes are observed in the area of the Prut River near the villages of Lenkivtsi and Streletsky Kut. The highest values of deviations of the channel from the current location are in the range of 300-400 meters.