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

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 Topl'a 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.324