| Summary: | Runoff processes at three hummock-covered hillslopes within a 95 ha catchment (Siksik Creek) in the tundra region of the Canadian western Arctic were studied for three years (1992-1994). Measurements over the study included all hydrological inputs, monitoring of active layer and water table depths, chemical tracer-based measurements of subsurface flow velocities, continuous and spot measurements of surface and subsurface discharges, detailed mapping of the hummock distribution and soil types, and continuous gauging of the main stream channel. Tundra is a heterogeneous medium in both horizontal (due to the presence of periglacial features such as mineral earth hummocks) and vertical (due to abrupt changes in hydraulic conductivity with depth) directions. Hillslope runoff occurs through the unfrozen saturated layer of the interhummock zone (IHZ), owing to its relatively high permeability and connected nature. The subsurface runoff rate is controlled by the saturated layer position and flowpath type. Subsurface flow follows downslope oriented flowpaths (primary and macrochannnel flowpaths), and flowpaths obstructed from conducting directly downslope (secondary flowpaths). The water velocity, discharge and residence time of the subsurface flowpaths are highly variable spatially and temporally as a result of variations in the thickness and elevation of the unfrozen saturated layer; and the composition and arrangement of flowpaths on hillslopes. Rapid subsurface flow (i.e. subsurface flow occurring at surface runoff-like velocities) occurs through the highly conductive near-surface peat as well as through macrochannels. Although surface runoff is rare, the task of transmitting runoff rapidly to the stream is accomplished by rapid subsurface flow. All flowpath types conduct runoff at similarly high rates when the saturated layer is within the highly conductive near surface peats. When the saturated layer is below this near-surface zone, but still within the depth range where macrochannels occur, the macrochannel ...
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