Research topics

The Belá River is a unique morphological-ecological water body in Slovakia. Together with its riparian zone, it creates a biocorridor of supraregional significance and, thanks to habitats of European significance (SKUEV0141), is included in the NATURA 2000 system. The subject of our initial research was to gain knowledge about the development of its wild-migrating floor plan over the last 180 years on the basis of data and data from the remote sensing data (1). In connection with the analysis of its response to extreme flood flows over the last 60 years (2), as well as changes in environmental conditions and human impact, we were able to clarify key factors influencing the dynamics of morphological changes and even predict the evolution of the Belá braidplain. Our research clearly pointed to a declining trend in the area of ​​the active riverbed, as well as the occurrence of flood events with low N-year (5-10) flow. It also points to the long-term degradation of the river system in the form of simplification of the braided-wandering planform to the wandering-meandering type (3), an increase in the area of ​​the islands, narrowing and straightening of the channel. Although it is possible to characterize the state of the Belá River as a threshold state of metastable equilibrium, it can be expected that the system will continue to be simplified. These assumptions were also confirmed by the application of the original methodology of research on the connectivity of coarse-grained sediments of the Belej riverbed (4). Eight types of potential functional connectivity were determined by interpreting the balance indices of connectivity at the level of floodplain-riverbed, riverbed-floodplain and bench-bench. By linear trend analysis of the integral connectivity index (IIC) and flood periods, it was found that all river sections show a decreasing trend of IIC values, i. j. a decrease in the movement of coarse-grained sediments and thus a decrease in the formation of benches and geodiversity and, consequently, biodiversity. Currently, our research focuses on regular monitoring of several river reaches, where we also use unmanned aerial vehicles (UAVs) and ground-based laser scanning (TLS) for data collection. Operational acquisition of very detailed orthophotos with a resolution of 5 cm and photogrammetric terrain models using UAV allows us a very accurate manual as well as automatic classification of internal trough structures and vegetation (5, 6). The laterally dynamic Belá River has washed the terrace. The TLS technique is therefore currently being used to identify the complex connectivity process of this active landslide and river bed. We see the application character of our results when optimizing the management of the Belá braidplain. The operation of a small hydroelectric power plant has a negative impact on the natural development of the riverbed and causes its intensive cutting into the clay subsoil. The flood in 2018 required the intervention of heavy equipment in the riverbed as part of the implementation of river training works (7) where the impact of these works on the hydraulic-morphological configuration of the multi-thread planform of the Belá River was analysed. The preservation of the natural properties of the morphology of the riverbed is closely related to the preservation of its ecological significance and function. Therefore, it is indisputable that among the most important input variables in the optimization of river management is, besides the identification of unstable river reaches, mainly the understanding of its internal self-regulatory mechanisms.

(1) KIDOVÁ, Anna – LEHOTSKÝ, Milan. Časovo-priestorová variabilita morfológie divočiaceho a migrujúceho vodného toku Belá = Spatio-temporal morphological variability of the braided-wandering River Belá. In Geografický časopis, 2012, roč. 64, č. 4, s. 311-333.

(2) KIDOVÁ, Anna – LEHOTSKÝ, Milan – RUSNÁK, Miloš. Geomorphic diversity in the braided-wandering Belá River, Slovak Carpathians, as a response to flood variability and environmental changes. In Geomorphology, 2016, vol. 272, p. 137-149.

(3) KIDOVÁ, Anna – LEHOTSKÝ, Milan – RUSNÁK, Miloš. Recent channel planform evolution of a braided-wandering river using multitemporal data and GIS (case study of the Belá River, Slovak Carpathians). In Acta Scientiarum Polonorum. Formatio Circumiectus, 2017, vol. 16, no. 1, p. 247-259.

(4) LEHOTSKÝ, Milan – RUSNÁK, Miloš – KIDOVÁ, Anna – DUDŽÁK, Jozef. Multitemporal assessment of coarse sediment connectivity along a braided-wandering river. In Land Degradation & Development, 2018, vol. 29, no. 4, p. 1249-1261.

(5) RUSNÁK, Miloš – SLÁDEK, Ján – KIDOVÁ, Anna – LEHOTSKÝ, Milan. Template for high-resolution river landscape mapping using UAV technology. In Measurement, 2018, vol. 115, p. 139-151. (2.218 – IF2017).

(6) RUSNÁK, Miloš – SLÁDEK, Ján – KIDOVÁ, Anna. Využitie UAV technológie pre klasifikáciu a mapovanie krajiny vo fluviálnej geomorfológii = Using UAV technology for landscape classification and mapping in fluvial geomorfology. In Geografický časopis, 2018, roč. 70, č. 2, s. 141-160.

(7) KIDOVÁ, Anna – RADECKI-PAWLIK, Artur – RUSNÁK, Miloš – PLESIŃSKI, Karol. Hydromorphological evaluation of the river training impact on a multi-thread river system (Belá River, Carpathians, Slovakia). In Scientific Reports, 2021, vol. 11, art. no. 6289.

Response to environmental changes of the morphological pattern of the studied river systems within the Slovak Carpathians we investigated to infer about the impact of flood events and environmental changes on the evolutionary trend of the river since the mid-twentieth century. Generally, more specific aims relate to identification periods with different flood magnitudes; to estimation the area and number of main channel forms for each of the periods using data from aerial photos; to interpretation the temporal evolution of the studied river systems based on the obtained data, including those concerning human impacts; to identification and interpretation the spatial variability of erosion and deposition areas.

Channel narrowing and incision cause isolation of the rivers from their floodplains. Stabilization of potential channel forms such as the transformation of bars into islands is usually observed. Anyway, this irreversible process can be iniciated by human intervention as we the most significantly noticed on the Belá River. The operation of the small hydropower plant required the bypass channel maintance what activated the progressive backward erosion.

Lateral channel shift results from bank erosion and aggradation, which in turn reflects the relationship between erosion processes and bank features (such as point bars). Lateral shift of the meandering channels generally seen as natural hazard because it threatens artificial man-made landscape structures (i. a. roads, arable land, and settlement). The Ondava River represents a good exemplar of recently very dynamic system with distinct lateral instability and bank erosion (see the picture below). The trajectory of its changes reflects the present dynamics of the system with variability of discharges during flood events. The overal average shift of the Ondava channel oscillated between 21.7 m (1987-2002) and 8.1 m (2002-2009).

Direct and indirect human activities lead to major changes in water and sediment fluxes, which result in changed river corridor characteristics in Slovakian river systems as well as worldwide. Human activities as a dike construction, small hydropower plant operation or gravel extraction influencing river morphology and contribute to the reduction in sediment supply, to channel straightening, channel narrowing as well as to disruption of the lateral and longitudinal sediment or hydraulic connectivity. Hence, the sustainable river management should be respect the economic, ecological as well as the geomorphological criteria hand in hand with river monitoring and restoration works.

Incised Belá River into the flysch subsoil as a geomorphological effect of a flood
in the summer of 2010 (a), a flood protection dam in the urban area of Liptovský Hrádok, Belá
(b) as an example of an irreversible change in the morphology of the riverbed; significant gravel mining on Ondava as anthropogenic factor of changes in the riverbed (c) and incising of the Ondava River into the subsoil formed alternating sandstones and claystones with a maximum depth of 1.9 m (d).
Source: Rusnák M., Kidová A. (2018) Recent morphological changes of Slovak watercourses Belá
and Ondava in the Western Carpathians from the second half of the 20th century. Geographia Cassoviensis.