Fluvial response of the lowland Middle Tisza River to centurial regulation works

The Tisza River (Central Europe) has a long regulation history. In the 19th century, artificial cut-offs and flood-mitigation levees were built, followed by revetments and dams. Simultaneously, a geodetic survey network was established, providing a uniquely dense and long-term channel database. We aimed to evaluate the fluvial response of the Middle Tisza River (234 km) to engineering works using a large number of channel cross-sections (94) surveyed between 1890 and 2017. Artificial cut-offs (1846–1890) resulted in incision (1.9–2.7 cm/y) and widening (0.2–1.6 m/y), and the channel reached equilibrium within 30–60 years. Revetment and groyne construction disrupted this state (1930–1960). In response, the channel incised (0.9–6.2 cm/y), and the narrowing decreased the cross-sectional area significantly. When the cross-sectional area falls below 1500–1550 m², the channel incises or widens rapidly, leading to revetment collapse after 20–40 years of its construction. This response was overlapped by the effects of dam constructions. In the reservoirs, sediment sedimentation counteracted incision, while downstream of dams, incision was accelerated by clear-water erosion. As a result of intensive vertical erosional processes, the cross-section shapes transitioned from trapezoidal to V-shaped, and they became more uniform than during the 19th century due to the uniform flow conditions in the straightened channel. The findings can be used to assess the impacts of future river training works. • Nowadays, erosional processes dominate the naturally meandering Tisza River. • Artificial cut-offs led to incision (2.7 cm/y) and channel widening (1.6 m/y). • Revetments caused incision (6.2 cm/y), narrowing, and a decline in cross-sectional area. • Erosional processes ceased in reservoirs, but downstream of dams they amplified. • The trapezoidal channel became V-shaped, and the hydraulic geometry became uniform.