Subsidence in the Seville urbanized alluvial plain from MT-InSAR (Guadalquivir basin, southern Spain)

Abstract

The Neogene-Quaternary Guadalquivir foreland basin is located at the frontal part of the Betic Cordillera, in southern Spain. Sevilla city was built on the alluvial plain of the lower part of the basin. The most recent sediments are fluvial deposits of the Guadalquivir river, that is the main watercourse of southern Iberian Peninsula, flowing towards the Gulf of Cadiz and Atlantic Ocean. The river channel was modified to reduce the impact of the floods and to improve the access of Sevilla harbor. A multidisciplinary approach, including Multi-Temporal InSAR (MT-InSAR) and borehole data has been applied to reveal the drainage network below the city. The most recent sediments of the Guadalquivir river are under-consolidated and highly sensitive to compaction. Subsidence of the Sevilla city, in the period comprised between 2003 and 2010, was influenced by the geotechnical parameters of the fluvial deposits and also by the evolution of the aquifer water table level. The fine-grained sediments undergone the highest subsidence rates. Moreover, the thickness of each sedimentary layer also contribute to a different subsidence behavior in each zone. Subsidence data provide new insights to constrain the spatial distribution of the drainage network and the architecture of the fluvial deposits with paleochannels below the city. Most of the highest subsidence rates occur in the western margin of the river and its tributaries. The eastern margin is more stable because it is formed by consolidated coarse-grained sediments of fluvial terraces. The river water level has higher impact on the aquifer water table and subsidence than the rainfall, probably due to the absence of direct infiltration in urban zones and human regulation of the river flow. The subsidence estimated with MT-InSAR was used to underline the paleochannels related to recent fluvial networks in urban covered areas.