In situ measurement of meltwater percolation flux in seasonal alpine snowpack using self potential and capillary pressure sensors

Abstract. Downward flux of percolating meltwater was measured quantitatively in an in situ vertical profile, in an alpine snowpack, at a remote location. Three separate measurement systems were used to obtain multiple parameters required to calculate percolation flux. Brooks-Corey constitutive parameters were measured in a 0 °C isothermal snow sample test cell, and then applied to an on-site snow column test. The instrumented column test allowed calculation of fluxes, that were then calibrated to measured outflow to empirically determine an appropriate value of zeta potential. In situ measurements with data logging of self-potential (SP) and capillary pressure sensors then allowed calculation of flux from SP measurements (q_sp), expressed as darcy velocity, over a multi-day period. The results strongly reflected diurnal snow melt dynamics, and daily peak q_sp ranged from 5.6 to 105 cm/d. q_sp was comparable to actual fluxes, represented by changes in snow water equivalent (SWE) (2.5 to 5.3 cm/d) measured at an adjacent USDA SNOTEL station. The average error in q_sp was 8 % over a four-day period, with total calculated flux of 18.1 cm, compared to a 16.8 cm change in SNOTEL SWE. Daily (24-hour period) errors ranged from +26 % to −47 %. The methodology developed herein can combine SP with either capillary pressure or saturation measurements. The ability to measure meltwater percolation flux in snowpacks may support mathematical modeling of unsaturated flow processes in melting snow, and may supplement studies of snowmelt-groundwater and snowmelt-runoff interactions and glacier mass balance studies.