InSAR Assessment of Ground Deformations in Shoreline Urban Areas Associated to Hydraulic Head Variations

Abstract:

Monitoring ground deformations in highly dense populated shoreline and lowlands areas such as Montreal is crucial for the sustainable development of urban infrastructures. Montreal already undergoes house foundations damages with a density of 8 repairs per square kilometer, especially over clay deposits such as in the Plateau neighborhood with a density of 89 repairs/km². Using Radarsat-2 C-Band SAR interferometry, we observe a 3–5 mm ground LOS displacement variation temporally out-phased by three months relative to the 2 meter subartesian aquifer hydraulic head and river level variations, over a 60 km² zone located in the central part of the Montreal Island in eastern Canada, from 2008 to 2010. Using ascending and descending SAR acquisition mode we extract the vertical component of the LOS velocities and observe secular displacements relative to a unconfined aquifer. These displacements are 2 mm/year subsidence on the minor topographic high, associated with evapotranspiration. We also observe ground water recharge and ~1 mm/year uplift downhill related to ground water discharge from deep regional aquifer enhanced with a faults system and shallow local aquifer arising from transmissivity. Displacements observed during this two year study are small but they are significant if integrated over the average lifetime of a house. We conclude that hydraulic head is related to the observed ground deformation in most of the areas of Montreal. Moreover, wetter climate conditions forecast for this area will definitely increase the aquifer dynamics; thus, more ground deformations are foreseen and have to be considered in future infrastructure design standards.