InSAR Assessment of Surface Deformations in Urban Coastal Terrains Associated with Groundwater Dynamics

Monitoring ground deformations arising from groundwater dynamics in dense urban coastal terrains is crucial for the sustainable development of infrastructures in these highly populated areas. The city of Montreal, which is located in the Saint-Laurent plain in eastern Canada, with its fast-growing populations, is a unique case study for other similar cities in coastal terrains. The city undergoes high-level house foundation damages with densities reaching up to 89 repairs/km² resulting from time-dependent ground deformations that are correlated to groundwater dynamics and evapotranspiration. Using Radarsat-2 C-Band synthetic aperture radar interferometry, we observe 3-to 5-mm ground line-of-sight displacement variations temporally outphased by few months relative to the 2-m subartesian aquifer hydraulic head variations. The deformations are observed over a 60-km² area located in the central part of the Montreal Island in Canada, from 2008 to 2010. We observe displacements of ∼1 mm/year uplift in the areas covered by 15-m-thick clay layer. These displacements are well correlated to the number of house repairs. We also observe ∼2 mm/year subsidence on elevated terrains, associated with evapotranspiration. The amplitudes of the displacements observed during this two-year study are significant when integrated over the average lifetime of urban structures. We conclude that the observed ground deformations are related to the seasonal variation of hydraulic head in most of the areas of Montreal. Moreover, wetter climate forecasts over upcoming decades for this area, will accentuate groundwater level fluctuations; thus, more ground deformations are foreseen, and have to be considered in future infrastructure design standards.