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.@en

Major rivers have traditionally been linked with important human settlements throughout history. The growth of cities over recent river deposits makes necessary the use of multidisciplinary approaches to characterize the evolution of drainage networks in urbanized areas. Since under-consolidated fluvial sediments are especially sensitive to compaction, their spatial distribution, thickness, and mechanical behavior must be studied. Here, we report on subsidence in the city of Seville (Southern Spain) between 2003 and 2010, through the analysis of the results obtained with the Multi-Temporal InSAR (MT-InSAR) technique. In addition, the temporal evolution of the subsidence is correlated with the rainfall, the river water column and the piezometric level. Finally, we characterize the geotechnical parameters of the fluvial sediments and calculate the theoretical settlement in the most representative sectors. Deformation maps clearly indicate that the spatial extent of subsidence is controlled by the distribution of under-consolidated fine-grained fluvial sediments at heights comprised in the range of river level variation. This is clearly evident at the western margin of the river and the surroundings of its tributaries, and differs from rainfall results as consequence of the anthropic regulation of the river. On the other hand, this influence is not detected at the eastern margin due to the shallow presence of coarse-grain consolidated sediments of different terrace levels. The derived results prove valuable for implementing urban planning strategies, and the InSAR technique can therefore be considered as a complementary tool to help unravel the subsidence tendency of cities located over under-consolidated fluvial deposits.

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Seville, with a metropolitan population of about 1.5 million, is the capital and largest city of Andalusia (S Spain). It is the 30th most populous municipality in the European Union and contains three UNESCO World Heritage Sites. The Seville harbour, located about 80 km from the Atlantic Ocean, is the only river port in Spain. The city is located on the plain of the Guadalquivir River. Using Multi-Temporal InSAR with ERS-1/2 and Envisat data a subsidence behavior is detected in the period 1992-2010. The geometry of the subsiding areas suggests that it should be conditioned by the fluvial dynamics of the Guadalquivir River and its tributaries. Facies distribution along the fluvial system (paleochannels, flood plains.), with different grain size and matrix proportion, may explain the relative subsidence between the different sectors.@en