Estimation of equivalent permeability of snowpack using a snowmelt lysimeter at Patsio, northwest Himalaya

Abstract

The meltwater percolation process through the snowpack greatly influences its physical and mechanical properties. The percolation process is important for understanding the spring avalanche phenomenon as well as the meltwater runoff for basin hydrology studies. The permeability of individual snow layers depends on parameters such as porosity, pore connectivity and the geometrical shape of the pores. Snowpack equivalent permeability plays an important role in governing the transmission of meltwater through the different layers of the snowpack. In this paper, we present the design, fabrication and installation of a snowmelt lysimeter at Patsio field research station, Himachal Pradesh, India, and determine the snowpack equivalent permeability using lysimeter discharge data. The snowmelt lysimeter, having a collector area of 6.25 m2 and a high-capacity snowmelt measuring tipping bucket, was installed on flat ground near the observatory with a data acquisition system. Snowmelt discharge measurements were made for two melt seasons, 2006/07 and 2007/08. Snow and meteorological data were collected at 15 min intervals using a semi-automatic weather station. The hourly surface snowmelt was estimated using an energy-balance approach. The maximum daily discharge was >2 mm w.e. h -1 for most of the observation period. The daily mean wave speed of the meltwater front varied from 109 to 285 mm h-1 for a daily mean discharge range of 0.6-1.8 mm w.e. h-1, while wave speeds for a particular melt flux of 2 mm w.e. h-1 varied between 113 and 486mmh-1. The pore-size distribution index was estimated using the power-fit relation between wave speed and discharge. The equivalent permeability of the snowpack was found to vary between 3.4 × 10-8 and 9.9 × 10-12 m2.