The Large-Scale Hydraulic Conductivity for Gravitational Fingering Flow in Unsaturated Homogenous Porous Media: A Review and Further Discussion

Gravitational fingering often occurs for water flow in unsaturated porous media. This paper reviews a recent effort developing macroscopic theory to describe the gravitational of homogeneous and soils, based on optimality principle that flows soils such manner generated patterns correspond minimum global resistance. The key difference between new conventional theories is hydraulic conductivity not only related saturation or capillary pressure, but also proportional power function flux, because flux closely allows large conductivities at locations where fluxes are as well minimize resultant relationship fraction zone compared with obtained from parallel fractal nature patterns. relationships two efforts found be essentially identical gravity-dominated can both expressed saturation. work demonstrates theoretical values exponent vary relatively narrow range 0.75 0.80 most which supported by observations previous field tests. remarkable finding makes it easy apply sites experimental data readily available estimating value. potential limitations suggested future research topics area discussed.