Deformational behaviours of alluvial units detected by advanced radar interferometry in the Vega Media of the Segura River, southeast Spain

Abstract

It is widely known that differential land subsidence in a valley significantly controls its fluvial dynamics. Nevertheless, major uncertainty exists about the way in which alluvial forms respond to this process. In this study, morphological and lithostratigraphic data have been combined with advanced differential interferometry (A-DInSAR) to detect changes in alluvial landform elevations and to verify the existence of a differential subsidence pattern influenced by active sedimentary dynamics. For this purpose, the middle reach of the Segura River valley (Vega Media of the Segura River), in southeast Spain, was chosen as the study area. The Vega Media of the Segura River is an alluvial area affected by subsidence processes in close conjunction with depositional conditions, ground-water withdrawals and faults. A high scale mapping of the main younger sedimentary units was carried out by combining multi-temporal aerial photographs, high-resolution digital elevation models derived from LIDAR data, global navigation satellite system data and fieldwork. In addition, lithostratigraphic descriptions were obtained from geotechnical drilling and trenching. Finally, ground surface displacements, measured using A-DInSAR for the periods 1995–2005 and 2004–2008, allowed the determination of elevation rates and ground deformation associated with the different alluvial units. The results from this analysis revealed four typical deformational behaviours: non-deformational units (cemented alluvial fans and upper fluvial terraces); slightly deformable units (lower terraces and old abandoned meanders); moderately deformable units (lateral accretion zones and abandoned meanders before channelisation in 1981); and highly deformable areas (recently active meanders associated with artificial cutoffs by channelisation, non-active floodplains and spilling zones).