In recent decades, in the Pre-Carpathian region of Ukraine during the summer period, floods and flood events became more frequent. They were accompanied by significant economic and environmental loss. Especially powerful were the floods of 2008 and 2020, but the floods in 2014 and 2016 also had destructive consequences. Therefore, the study of river channel processes, river stability and assessment of flooded land areas due to floods is an urgent problem. The aim of the study is to propose a methodology for hydrological modeling of sections of riverbeds with complex morphometric and hydrological characteristics. The construction of a digital elevation model (DEM) and the selection of the distance between the cross-sections, as well as the determination of the Manning coefficients, have the greatest impact on the accuracy of the modeling, so these factors should be given maximum weight when calibrating the model. The object of the study was the section of the Dniester River in Ukraine in the place of transition from the foothill part of the channel to the hilly–marshy part with complex meandering and significant shifts of the river. The methodology of hydrological modeling includes three principal components: construction of the DEM, determination of the type of underlying surface and determination of the level of water rise in the riverbed. The research was carried out on the basis of imaging from unmanned aerial vehicles (UAVs). In 2017, the imaging of a section of the Dniester riverbed was carried out in the summer during a period of significant vegetation growth, which affected the accuracy of determining the heights of the model points. According to the results of this imaging, the residual mean square (RMS) for determining the heights of the points exceeded the permissible value of the RMS (0.25–0.3 m) by two times. In 2021, imaging was performed in the autumn period when there was no leaf cover. The RMS of the DEM for 2021 imaging was 0.26 m. According to the results of the survey in 2017 and 2021, orthophotoplans were created, which were used to determine the planned displacements of the river bed and clarify the Manning coefficients, which characterize the roughness of the underlying surface. The value of the water level rise was obtained on the basis of the graph on the date of the maximum rise of the water level on 24 June 2020 according to the hydrometeorological station located near the selected area. The result of the research is hydrological modeling using the HEC-RAS module for a site with complex hydrological and morphometric characteristics on the date of the maximum water rise. It was established that in order to achieve the required accuracy of the DEM, imaging should be carried out in the leafless period of the year, since the accuracy of constructing the DEM decreases by half during the growing season. On the basis of the obtained orthophoto plans, a methodology for determining refined Manning coefficients was developed, which allows taking into account changes in the underlying surface of the channel area. The area of the flooded area was calculated based on the level of water rise during the 2020 flood.
The aim of the work is to investigate the accuracy of the DEM of nearshore areas using UAV material. One of the important issues in hydrological flood modelling is the high accuracy of the DEM. In the case of a complex relief type, which is associated with meandering riverbeds, it is proposed to use UAV surveys to create a DEM. Hydrological modelling involves the following main steps: creation of high precision DEMs, determination of Manning coefficients to account for the influence of the underlying surface and determination of water level changes based on the water level graph derived from observations at hydrometeorological stations. This research presents the construction of a high-precision DEM, based on a UAV survey. For high-precision modeling, the fundamental issue is the consideration of vegetation in the nearshore areas and the choice of the optimal time period for the survey. The aim of the study is to develop a methodology for the construction of a high-precision DEM from UAV data, investigate the possibilities of eliminating the influence of vegetation on point marks using software methods, determine planned channel shifts and compare the accuracy of DEM construction for surveys conducted in June 2017 and in November 2021. The section at the transition from the mountainous to marshy-hilly part of the Dniester River near the town of Stary Sambir, with complex morphometric and hydrological characteristics of the channel and banks at the site of the complex meandering of the river in a rugged ravine area was the study object of this work. Results. It was found that for 4 years between two surveys, the planned displacements of some points are up to 25-31 meters. A priori estimation of coordinates determination by points from the GNSS-receiver was carried out, the accuracy of point coordinates determination is 2-3 cm. The a priori estimate of the accuracy of determining the coordinates of points from the input survey data is: for plan coordinates - 4-6 cm for two survey periods, the error in determining the marks of points for different values of the baseline - 21-31 cm. It has been established, that the program methods of accounting of influence of high vegetation do not give the possibility of its full accounting, the average square error, in places of such vegetation makes 0,64 m. Therefore, it is necessary to carry out UAV survey in the leafless period of the year, early spring or late autumn. Scientific novelty consists in the study of the possibility of constructing a high-precision DEM for different types of vegetation from materials obtained from UAVs. The results can be used for hydrological modeling of river channels with complex hydromorphological characteristics.
The purpose of the work is to investigate the digital elevation models of the mass grave of 1944, built on the basis of aerial and cartographic data of different times. The implementation of the task involves the construction of digital elevation models (DEM) on the territory of the Jewish mass grave in the city of Vynnyky and Italian prisoners of war near the city. On the territory of the Jewish mass grave in the city of Vynnyky, a DEM was created based on a stereo pair of archival aerial images obtained in 1944 and on the basis of aerial photography from a UAV conducted in 2015. Since archival aerial photographs did not contain orientation elements, they were geometrically transformed using the ErdasImagine software. After that, the stereo pair was processed in the program Digitals, where relief elements on the territory of the mass grave were obtained. Aerial photography from a UAV on the territory of the city of Vynnyky provided the data which was processed in the Agisoft PhotoScan software. It allowed us to create an orthophoto plan and an elevation map of the city territory. Elements of relief on the territory of the mass grave of 1944 and 2015 were imported into the Surfer software environment, where 3D digital elevation models were built. Since the territory of the grave did not have significant differences in height, and the relief was quite gentle, the method of constructing the DEM of the Natural Neighbor was chosen, which gave a positive result. Analyzing the digital elevation model and the vector map for 1944, the border of the mass grave is clearly distinguished, since the height difference between its edges and the rest of the territory is from 20 to 36 cm, depending on the section of the border. The analysis of the digital elevation models and the vector map for 2015 of the territory of the mass grave determined from the aerial image of 1944 showed that the characteristic height differences on the former border of the grave are observed only in the left-right corner of the grave and on a separate section of the right border. Height difference indicators range from 15 to 20 cm. It should be noted that height differences are also observed in the rest of the territory belonging to the mass grave and outside it. This can be explained by many years of human intervention and agricultural land use. With regard to the investigation of the mass graves of Italian prisoners of war near the city of Vynnyky, the modern territory is 100% wooded, which makes it impossible to apply aerial photography. Therefore, in order to compare the modern DEM with the stereo pair of aerial images of 1944, it was decided to conduct a ground tacheometric survey of the area in 2011. Tacheometric survey data was exported to the dxf exchange format, after which it was opened in Surfer and the DEM was built. In this case, digital elevation models were built using the Kriging method, since the area where the mass graves are located is quite hilly with a significant difference in elevation. According to the digital elevation models, 54 pits with burials that have survived to this day have been identified. The scientific novelty of the work consists in the development of the concept of combining disparate data for the construction of digital elevation models and the creation of a complete picture of the study of the territory of the object of historical and cultural heritage. The received data can be used by the relevant cultural heritage preservation departments of the Ministry of Culture of Ukraine for their further study.
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