The interplay between resident water (“old water”) and infiltrating water (“new water”) in porous media was examined through experiments in an idealized, two-dimensional, glass micromodel. Image analysis was used to quantify the miscible interplay between old and new water during a cycle of imbibition by new water and drainage by air in a domain that was partially saturated with old water. The dynamics of the old–new water exchange were characterized in terms of several parameters: remaining old water, number of old-water pockets, volumetric fraction, and degree of mixing. In particular, it was found that some old water remained in the system at long times within stable water pockets; these pockets may remain stable even after a second cycle of infiltration.

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