Mapping subsurface defects and surface deformation along the artificial levee of the Lower Tisza River, Hungary

Abstract

Abstract Artificial levees along alluvial rivers are major components of flood risk mitigation. This is especially true in the case of Hungary, where more than one-third of the country is threatened by floods and protected by an over 4200 km long levee system. Most of the levees were built in the 19th century. Since then, several natural and anthropogenic processes, such as compaction, erosion, Etc., could contribute to these earth structures' slow but steady deformation. Meanwhile, as construction works were scarcely documented, the structure and composition of artificial levees are not well known. Therefore, the present analysis aimed to map structural differences, possible compositional deficiencies, and sections where elevation decrease is significant along a 40 km section of the Lower Tisza River. Investigations were conducted by real-time kinematic GPS (RTK-GPS) and ground penetrating radar (GPR). Onsite data acquisition was complemented with an analysis using a Persistent Scatterer Synthetic Aperture Radar (PSI) to assess general surface deformation. GPR data have shown that levee structures can significantly vary even in a few km on sections with the same construction history. GPR profiles showed several anomalies, including structural and compositional discontinuities and local features. The penetration depth of GPR varied between 3 and 4 m. Based on height measurements, the mean elevation of the levee crown decreased by 8 cm in a 40-year time span. However, elevation decrease could reach up to 30 cm at some locations. Sections affected by structural anomalies, compositional changes, and increased surface subsidence are especially sensitive to floods when measurement results are compared to flood phenomena archives.