Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

Abstract

Abstract. River deltas are dynamic coastal systems and their evolutions are closely monitored as it often concentrates vital natural resources for the surrounding areas. Many deltas worldwide experience subsidence due to geological processes (sediment loading and compaction) or human activities (groundwater or hydrocarbon extraction, land reclamation). This causes shoreline erosion or wetland loss which represent serious issues for the population. In this study we investigate the dynamic of the Var delta (France) where reclaimed lands over sea have been built to host the Nice côte d'Azur airport (NCA). Actually, the stability of this infrastructure is a permanent concern since, in 1979, a newly built extension of the runway platform collapsed in the sea, causing important damages. The project of land extension stopped, but the present airport platform is still located on reclaimed land. Factors that can trigger such catastrophic landslide are thought to be linked to the delta activity and the artificial airport platform load. We used, therefore, Envisat InSAR data to measure accurately the ground deformation of the area that includes the Var delta and NCA airport. Combining data from ascending and descending orbits, we estimated the east-west and vertical components of the deformation and obtained very accurate displacement rate (with a 1σ error of 0.25 mm yr −1 ). We found that nearly all the deformation is vertical and impacts the whole Var delta. The Var valley subsides at a very low rate (0.5-1 mm yr −1 ) but downstream the subsidence rate increases and a clear jump is observed at the transition with the reclaimed lands (1-2 mm yr −1 ). On average, the reclaimed lands subside at 3 mm yr −1 . Since the subsidence rate increases in correlation with the sediment thickness, we interpret it as the compaction of the delta quaternary sedimentary wedge. In addition, three areas subside faster (between 5 and 10 mm yr −1 ), with one calling for more attention as it is the largest and overlooks the steep Var canyon. The progressive increase of subsidence rates toward the sea also suggests that the underwater parts of the margins could subside at rates well above 10 mm yr −1 .

Strong Site Effect Revealed by a New Broadband Seismometer on the Continental Shelf Offshore Nice Airport (Southeastern France)

“…Because of the 1979 event, several studies have already characterized the stability of the Nice continental slope using morpho-bathymetry investigations (Klaucke and Cochonat 1999;Migeon et al 2012;Kelner et al 2016), Envisat INSAR data (Cavalié et al 2015), in situ measurements (Stegmann et al 2011;Steiner et al 2015;Sultan et al 2010), laboratory experiments (Kopf et al 2016;Mulder et al 1997;Stegmann and Kopf 2014), and numerical modeling (Dan et al 2007;Steiner et al 2015). Only a few studies (Sultan et al 2004;Dan et al 2007;Ai et al 2014) have focused on the potential effects of the seismic waves of an earthquake on the airportslope stability, in order to answer the crucial question: could local seismic waves trigger a major landslide?…”

Sentinel-1A for monitoring land subsidence of coastal city of Pakistan using Persistent Scatterers In-SAR technique

“…Analyzing and monitoring subsidence in large cities allows meaningful insights for mitigating the probable loss of property and life due to increasing development rates in many regions around the globe 1 . A range of variables that could produce urban subsidence includes human and natural reasons such as building loads 2 – 4 , lithology 2 , 5 – 7 , groundwater consumption 3 , 8 , 9 , tectonic activity 3 , 10 , dewatering 11 , seasonal effects 12 , mining activities 13 . Each of these variables might have a unique impact on surface deformation.…”

A Model for Complex Subsidence Causality Interpretation Based on PS-InSAR Cross-Heading Orbits Analysis

“…Monitoring and analyzing subsidence in urban areas provides actionable intelligence for the prevention of potential loss of life and property, given the high rates of urbanization in many parts of the world. A variety of factors could produce urban subsidence including natural and anthropogenic causes such as lithology [1][2][3][4], dewatering [4,5], tectonic activities [6,7], building loads [3,6,8], Mining activities [9], and groundwater consumption [6,[10][11][12]. One of those factors could individually influence the surface subsidence.…”