Miloš Rusnák

Geomorphic/Sedimentary Responses of Rivers to Floods: Case Studies from Slovakia

The aim of this study is to outline the geomorphic/sedimentary responses of three Slovak river systems of different character (a non-channelized meandering gravel-bed river, a mixed-bedrock headwater river, and a channelized section of a large alluvial river) to extreme flood events. Lateral channel shifts and the spatial variability of channel landforms as responses of a non-channelized gravel-bed stream to flood events were studied on a 13.2 km long reach of the Ondava River in two time horizons, 2002 and 2009 (reference year: 1987). Two different methods were used to quantify the geomorphic effect of floods on the Topl’a River. First is the analysis of the remotely sensed imagery before (September 2006) and after (October 2009) the July 2008 flood. Second is the analysis of representative cross sections measured on each of the 78 delimited channel reaches. Lithofacies studies of the Danube River overbank deposits were conducted on the right-bank inter-dike inundation area (active floodplain) of 300–600 m width. Case studies prove that the responses of different river systems to floods are governed by a combination of ‘global’ laws and ‘local’ spatial and/or temporal factors (different settings and scales).

Channel migration inferred from aerial photographs, its timing and environmental consequences as responses to floods: A case study of the meandering Topľa River, Slovak Carpathians

Abstract The bank erosion area, rate of bank retreat and overall geomorphological and financial effects of channel migration due to recent flood events (over the time span 1987–2009) are identified using remotely sensed data and GIS. A 39 km-long reach of the meandering, gravel bed Topľa River (Flysch Slovak Carpathians) was selected as the study area. Based on the analysis of culmination discharges, two different flood periods are identified. The first one (1987–2002) is characterised by the dominance of low magnitude flood events, compared to the second one (2002–2009) with higher magnitude floods. Aerial photographs from 2002 and 2009 were chosen as a way to capture the morphological changes that occurred after the flood periods, while those from 1987 served as the reference point. In total, an area of 85.2 ha was eroded and 60.1 ha were deposited. The average channel shift per year doubled from 0.8 m/year (1987–2002) to 1.6 m/year (2002–2009). The most eroded land cover category in the riparian zone is floodplain forest, followed by arable land, grasslands and pastures and shrubs. From an economic point of view, the eroded floodplain with arable land and grassland (€ 29,924.02 in total) is a negative consequence of channel migration.

EVALUATION OF LAND COVER CHANGES AND BLACK LOCUST OCCURRENCE IN AGRICULTURAL LANDSCAPE. CASE STUDY: PODOLIE AND ČASTKOVCE CADASTRAL AREAS, SLOVAKIA

This study presents spatial analysis of agricultural landscape changes in the Podolie and Castkovce cadastral areas since 1949. Data for analysis was obtained from historical aerial photographs (from 1949, 1986 and 2006), detailed field mapping and Black locust ( Robinia pseudoacacia L.) monitoring. Land cover changes were assessed from the aerial photographs based on the CORINE land cover legend, environmental variables were derived from digital elevation model (DEM) and detailed geological and soil maps. Data was spatially compared and assessed by regression analysis for interpretation of Black locust occurrence. The most significant land cover changes occurred between 1949 and 1986 when agricultural areas were replaced by forest and semi-natural areas. One of the aspects of landscape changes is abandonment of agricultural landscape and occupancy this new transformed surfaces by invasive plant taxons (e. i. Robinia pseudoacacia L.). Black locust occurrence was mainly influenced by landscape management changes and subsequent land cover changes (afforestation from 1949 to 1986), especially in regions of dispersed settlements (Podolske and Korytnianske kopanice) after agricultural collectivisation. Environmental variables had little effect on Black locust expansion in these areas.