The hydrology of the proglacial zone of a high-Arctic glacier(Finsterwalderbreen, Svalbard): Sub-surface water fluxes and complete water budget

Proglacial areas receive fluxes of glacial meltwater in addition to their own hydrological inputs and outputs, while in high latitudes the seasonal development of the active layer also affects their hydrology. This paper supplements a previous study of the surface and atmospheric water fluxes in the proglacial area of the Svalbard glacier Finsterwalderbreen (77° N), by focusing on the sub-surface water fluxes of the active layer, and bringing together all the components of the proglacial water balance over a complete annual cycle. Particular attention is given to the transitional zone between the moraine complex and the flat sandur. Sub-surface water in the moraine complex (sourced mainly from snowmelt, lake drainage and active-layer thawing), is exchanged with sub-surface water from the sandur (sourced mainly from glacier-derived snow- and ice-melt), across a largely distinct boundary. Hydraulic head and specific discharge were monitored in a transect of wells spanning this boundary. A hydraulic gradient from the moraine complex to the sandur is maintained throughout the melt season, although this is reversed first briefly when glacial runoff floods the sandur, and then diurnally from mid-melt-season, as peak daily flow in the proglacial channel network drives sub-surface water in the sandur towards the moraine complex. It is estimated that the active layer does not freeze up until mid-December at this location, so that sub-surface water flow may be maintained for months after the cessation of surface runoff. However, the magnitude of sub-surface flow is very small: the total, annual flux from the moraine complex to the sandur is 11 mm, compared with 1073 mm of total, annual runoff from the whole catchment (glacier included). Furthermore, when considering the water balance of the entire proglacial area, there are unlikely to be significant, seasonal storage changes in the active layer.