Venice uplift by seawater injection in a randomly heterogeneous aquifer

Recent numerical analyses indicate that injecting seawater into a 600~800 m deep brackish aquifer underlying the Venice Lagoon might induce a land uplift of a few tens of centimeters over 10 years with a very significant mitigation of the floods that periodically plague the city. In real porous media, however, the hydraulic conductivity of the injected formation may exhibit a strong heterogeneity which could impact on the uniformity of the expected heave. The present communication investigates the influence of a seawater injection in a randomly heterogeneous aquifer with particular reference to the differential vertical displacements predicted at the ground surface. A Monte Carlo simulation is carried out assuming a log-normal stationary process of the hydraulic conductivity, namely the most important and naturally variable parameter, with a sensitivity analysis performed on the variance σ2 of the associated random field. The results indicate that gradients larger than those currently experienced in Venice at the building and monument scale are never attained irrespective of σ2 and despite the possible highly uneven expansion of the injected formation because of the smoothing effect exerted by the 600-m thick overburden.