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Water percolation within a deep snowpack field investigations at a site on Mt. Seymour, British Columbia Wankiewicz, Anthony Cyril


The capillary pressure and flux were measured in an old wet snowpack on Mt. Seymour, British Columbia, using tensio-meters and tension lysimeters. The flux was regulated from 0.01 to 10 cm/hr within snowplots, using isolation covers and irrigation at the snow surface. The tensiometers measured small-scale changes of capillary pressure in. both space and time. The extremes of pressure measured during fine weather snowmelt were -4 and -14 cm(H₂O). The vertical gradients of pressure were much smaller than the gravitational potential gradient with steady or decreasing flows (the gravity drainage postulate) but could be larger at a wetting front. Assuming Darcy's equation describes unsaturated flow, the gravity drainage postulate means that flux measurements during steady or decreasing flow could be interpreted as hydraulic conductivities. Snow lysimeters with an interface pressure of -25 cm (H₂O), were used to measure fluxes over the. small scale necessary for comparison with pressure and liquid water content changes within snow layers. The height of the lysimeter rim was selected to theoretically make the flow collection 100% efficient. The hydraulic conductivity-capillary pressure relations for snow describe hysteresis loops between boundary drying and wetting curves. The boundary curves follow power functions with an exponent between 11 and 15, the ratio of pressure between the two curves being 1.4. The derivative of hydraulic conductivity with respect to liquid content, when expressed as a ratio to the hydraulic conductivity itself (the fractional derivative), was found to be a slowly changing, function of the snow's hydraulic conductivity. The fractional derivative would equal the ratio of flux-wave speed to flux in the kinematic wave analogy. It had values of 60 to 125 over a 0.05 to 5 cm/hr range of hydraulic conductivity, according to the results from three different experimental methods (liquid water content changes, wetting front speeds, and drainage wave speeds).

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