Runoff and infiltration estimates based on pore pressure changes in shallow aquitards

ABSTRACT: The pore pressure time series that are recorded by piezometers installed in clay aquitards can be used to study the local water budget. For deep aquitards, pore pressure time series corrected for barometric pressure changes and earth tides can be related to the moisture loading at the top of the soil profile. When compared with precipitation and evapotranspiration, the moisture loading allows runoff and infiltration to be calculated. For shallow aquitards, the pore pressure record can be more complex as pore pressure changes due to seasonal fluctuations of the water table are superimposed on the total stress changes due to moisture loading. In this study, a finite element model was developed with COMSOL Multiphysics and its MATLAB LiveLink interface to calculate the moisture loading from complex pore pressure record in shallow aquitards. The MATLAB script discretizes the simulation in a series of time steps. The script iterates on the total stress boundary condition for each time step to replicate the pore pressure measured in the field. The paper presents a case study for the Sainte-Marthe test site in near Montreal, Canada.