Linking Runoff to Groundwater in Permafrost Terrain

Frozen materials with abundant ground ice are impermeable to groundwater movement and storage. Suprapermafrost groundwater in the active layer (seasonally frozen and thawed zone) is limited in quantity but important for runoff generation. Subsurface flow of this shallow groundwater normally follows soil pipes or through the soil matrix, the latter being strongly influenced by the hydraulic conductivity of the soil material, notably peat which commonly forms the top horizon. Exfiltration of this water gives rise to various expressions of surface runoff that include saturation overland flow on slopes, rills and gullies and drainage along ice-wedge cracks, wetlands or ponds. In discontinuous permafrost areas, deep groundwater from subpermafrost zone can also feed to wetlands, lake beds and streambeds or emerge as springs that may be thermal or saline in nature. Deep groundwater is especially important in karst areas where solution conduits in carbonate rocks provide subterranean flow passages. Suprapermafrost groundwater is not a reliable source for streamflow but subpermafrost groundwater discharge offers a stable base flow for rivers in discontinuous permafrost terrain.