“…Over the last 40 years, gravity‐driven fingering (GDF) within water‐wettable porous materials has been observed and studied in many laboratory and field experiments [e.g., Palmquist and Johnson , 1960, 1962; Tabuchi , 1961; Peck , 1965; Hill and Parlange , 1972; Raats , 1973; White et al , 1976, 1977; Diment and Watson , 1985; Glass et al , 1988, 1989a, 1989d, 1990; Baker and Hillel , 1990; Selker et al , 1992a, 1992c; Lu et al , 1994; Liu et al , 1994a, 1994b; Nicholl et al , 1994; Babel et al , 1995; Hendrickx and Yao , 1996; Yao and Hendrickx , 1996; Selker and Schroth , 1998; Wang et al , 1998a, 1998b; Nissen et al , 1999; Geiger and Durnford , 2000; Sililo and Tellam , 2000; Yao and Hendrickx , 2001]. Additionally, a number of investigations have focused on theoretical aspects of this phenomenon and its simulation using a variety of approaches [e.g., Philip , 1975; Parlange and Hill , 1976; Diment et al , 1982; Diment and Watson , 1983; Tamai et al , 1987; Hillel and Baker , 1988; Glass et al , 1989b, 1989c, 1991; Selker et al , 1992b; Chang et al , 1994; Chen and Neuman , 1996; Neumann and Chen , 1996; Glass and Yarrington , 1996; Nieber , 1996; Kapoor , 1996; Babel et al , 1997; Kacimov and Yakimov , 1998; Wang et al , 1998c; Geiger and Durnford , 2000; Ursino , 2000; Benson , 2001; Du et al , 2001].…”