UC Berkeley

The disconnect between pore-scale processes and continuum models of porous flow is a persistent problem in hydrogeology. Here, we present two drainage studies which attempt to bridge this divide. In the first, we demonstrate the sensitivity of continuum-scale drainage simulations to the critical nonwetting saturation, which is the saturation state of a voxel when nonwetting phase permeability becomes nonzero. To give this parameter a physical basis, we use laboratory observations of drainage in thin, backlit bead packs and Invasion Percolation simulations to propose a new percolation model for saturation as a function of distance behind the drainage front, incorporating Bond and capillary number dependency. In the second study, motivated by observations of streamflow responses to earthquakes, we test the hypothesis that seismic shaking can drain water out of the unsaturated zone. To accomplish this, we construct a sand chamber and monitor pore pressure during impact-induced shaking. We identify three distinct mechanisms: consolidation of sediments in the saturated zone, release of capillary water from the capillary fringe, and mobilization of isolated pore water in the unsaturated zone.