Floodplain levels and palaeo-channels: floodplain development along the Lower Tisza River
Abstract
Different floodplain levels developed along the Lower Tisza River, in connection with incisions since the Late Pleistocene. The present study aimed to classify the palaeo-channels based on their morphometry, to determine their bankfull discharge, to measure their OSL age, and to identify the floodplain levels based on their height. From the collected data-set we aimed to reconstruct the Late Pleistocene and Holocene development of the Lower Tisza Region.
Three phases of floodplain formation and two phases of incision were defined. However, significant time-span was found between the southern and northern parts of the region. The highest (C) morphological level was active from the beginning of the Late Pleniglacial (25.6±1.4 ka) in the southern part of the study area, thought in the middle and northern part of the study area the C-level was formed later (20.1±2.4–13.2±0.9 ka). At this time the Tisza had 4-5 times greater bankfull discharge (Qbf = 8615 m3/s). The first major incision started in the Ságvár–Lascaux interstadial (16.4±1.3 ka) around the Danube and Tisza confluence, but the incision reached the present-day confluence of the Maros River (ca. 175 km upstream) during the Late Glacial (13.1±1.2 ka). There is no great difference between the size of the paleo-channels on the C and B levels, so the incision was probably induced by tectonic activity. The B floodplain level was short-lived ca. 13 ka ago. During the last, but strongest incision phase (in south: 13.4±0.7 ka; north: 10.8±0.7 ka) the Tisza had smaller discharge (Qbf = 3306 m3/s), however the downstream divergence of the floodplain levels and the avulsions on the active floodplain (Level A) support the importance of the tectonic movements on the floodplain development. On the lowest, active A floodplain level 3,2±1,1–1,1±0,7 ka old meanders remained.
