Long-term hydrological changes after various river regulation measures: are we responsible for flow extremes?

Engineering works have affected the morphology of rivers (e.g., by cut-offs, artificial levees, revetments, and reservoir and dam constructions). These human impacts also have hydrological impacts, as they alter the natural channel geometry, affect the carrying capacity of the channel and confine the floodplains. The goals of the present paper are to analyse flow changes for the Tisza River (in Hungary) with its highly regulated channel using a long (141 y) daily hydrologic dataset and to evaluate the engineering works from the point of hydrological and morphological equilibrium. Since the late 19th century, the flood level along the Lower Tisza River has increased by 216 cm; further, since 1998, flood levels increased by over 80 cm without an increase in discharge. In addition, river stages for low flows have decreased, and the water slope has decreased. These changes are likely connected to morphological changes in the channel (e.g., incision, narrowing, disappearance of point bars, intensifying mass movements), which have been driven by the complex response to human impacts. While the channel could adjust itself to convey larger floods after the cut-offs, the revetments impede the channel adjustment and contribute to the hydrological and morphological disequilibrium state along the Tisza River.