Transient film flow on rough fracture surfaces

Transient film flow in unsaturated fractures was investigated conceptually and experimentally. By considering films on fracture surfaces as analogs to water in partially saturated porous media, the film hydraulic diffusivity and equation for transient film flow are obtained from their porous medium counterparts, the hydraulic diffusivity and the Richards equation. Experiments on roughened glass show that the average film thickness dependence on matric potential can be approximated as a power function. It is also shown that: the film hydraulic diffusivity increases with increased film thickness (and with increased matric potential). Fast film flow (average velocities greater than 3 x 10(-7) m s(-1) under unit gradient conditions) was observed for average film thicknesses greater than 2 mu m and matric potentials greater than -1 kPa.