Morphological Evolution of the Lower Tisza River (Hungary) in the 20th Century in Response to Human Interventions

Abstract

To understand the hydro-morphological responses of a river to engineering works is a key to future sustainable engineering projects. The Tisza River in the Carpathian Basin has been the subject of human interventions in the 19th-20th centuries, with regular monitoring since the first intervention. Therefore, it provides a unique opportunity to understand the long-term responses of a lowland river on engineering works. Here the interventions include the construction of embanked levees, artificial meander cutoffs, construction of revetments and groynes, and construction of lock-dams, whose differing effects can be analysed in detail. The Lower Tisza River, Hungary was shortened by up to a third of its 89-km length during late-19th-century regulation works. Simultaneously, it was disconnected from its 10-20 km wide natural floodplain, which was restricted to 1-5 km. Revetments were constructed along 25% of the banks since the early 20th century. This paper evaluates the effects of these regulation works on the Lower Tisza channel based on channel-surveys (1891, 1931, 1961, 1976 and 1999). Based on the results, the channel responded to every stage of the regulation works by adjusting its cross-sectional area, thalweg depth and bankfull width. From 1891 to 1961, the cross-sectional area of the channel increased in response to the artificial meander cutoffs through rapid incision and channel widening. The construction of revetments and groynes distorted this morphological development. After their construction, the cross-sectional area of the channel reduced by up to 50% between 1961 and 1976. The channel experienced incision and narrowing within this period. Whilst the morphological response of the river to cutoffs was improved flood conveyance, the revetments drastically decreased the flood conveyance; therefore, the flood levels increased without an increase in discharge, so the revetment constructions indirectly increased the flood risk.

Active point bar development and river bank erosion in the incising channel of the lower Tisza river, Hungary

“…In the morphology of the meandering Lower Tisza River, these processes refer to a loss of equilibrium. Based on our previous study (Amissah et al, 2018), the Lower Tisza has transformed from a meandering river by river regulation works. The intensive natural near bank processes have been reduced due to the construction of revetments aiming to stabilize banks.…”

“…It can be explained by the fact, that the erosion of the concave bank created favorable conditions (wide channel) for the development of the bar on the convex bank which translates and migrates downstream. On the contrary, at the revetted section at Csongrád, the point-bar develops in a confined channel, which is characterized by incision (Amissah et al, 2017(Amissah et al, , 2018. This incision also affects the point-bar's surface, lowering it, though smaller in-channel flood waves might deposit some material on the surface.…”

“…Its length was reduced by one third by artificial cutoffs in the late 19 th century. The shortened river and the subsequent doubled slope caused an increase in stream power which resulted in rapid channel incision (Amissah et al, 2018). Simultaneously, the wide natural floodplain (ca.…”

“…The Lower Tisza River like many other European rivers, has been subjected to various forms of human interventions: artificial levees were built to disconnect the river channel from its floodplains, artificial meander cutoffs were made to reduce the duration of floods, and bank stabilization measures including revetments and groynes were constructed ( Kiss et al, 2008;Amissah et al, 2018). The river as a result has transformed from a meandering river to an incising meandering one (incision has lowered base level while maintaining the meandering pattern with high bank walls), as it strives to re-establish a new equilibrium after the river training ( Kiss et al, 2008;Amissah et al, 2018). In recent times, some studies have shown that although the flood hazards have reduced due to higher flood velocities, there are threats to artificial levees due to increased lateral erosion (Kiss et al, 2019).…”

Bank Processes and Revetment Erosion of a Large Lowland River: Case Study of the Lower Tisza River, Hungary

“…Across the globe, studies on various rivers have documented the changes that humans have impacted on rivers through regulations [26,[31][32][33], including several rivers in Hungary [34][35][36]. River regulations generally modify the flow and sediment transport of a river channel, which affect both the channel form and river processes [37,38].…”