Preferential Flow and Melt Water Retention in Cold Snow Packs in West-Greenland

Abstract

Runoff from seasonal snow covers in Greenland provides the major source of stream flow in the non-glacierized catchments, and has gained interest in relation to hydropower potentials and water supply. During a two-month period the seasonal snow cover is melted and the discharge generated constitutes a major part of the annual runoff. Motivated by discrepancies between modelled and observed hydrographs during the early melt period in the Tasersuaq basin, we have performed tracer experiments in several pits and at different levels below the snow surface, to improve our understanding of water flow and storage in cold snow. It is observed that vertical percolation more readily occurs the deeper in the snow pack the tracer is sprinkled. At places where preferential vertical flow is established, we believe the water will eventually reach the bottom of the snow pack once it has passed the wind crusts on the top of the snow pack. From observations a parameterization of melt-water retention in the cold snow is suggested. We propose a time dependent term for the thermal and the gravity component, respectively, of storage in the snow pack. This time dependent term describes the fraction of snow which is exposed to melt water at the time when the water reaches the base of the snow. Incorporating such a term in hydrological models would improve them by providing an explanation of the observed fast hydrological response in the early melt period and by limiting the magnitude of the modeled peak flow.