A conceptual framework for runoff generation in a permafrost environment

Hillslope runoff processes were studied in the tundra region of the Canadian western arctic in order to provide a physically-based, conceptual framework for runoff generation for basins in this environment. It was found that subsurface flow is the dominant mechanism of runoff to the stream channel, that this flow is conveyed predominantly through the peat of the inter-hummock channels, and that subsurface flow through the highly conductive upper peat layer and soil pipes can be as rapid as surface flow. Stream discharge was computed from computations of hillslope runoff and meltwater input from the snowpack in the stream channel. The similarity between the computed and measured stream discharge suggests that the approach used to compute discharge would be useful as a conceptual basis for a distributed hydrological model for this environment. Hydrological interaction among the basin subsystems was found to play an important role in runoff generation. For example, when the water table was in the highly conductive upper peat layer, and discharge from inter-hummock channels was relatively large (∼0.1-1.0 m 3 d -1 ), the near-stream area, a zone of relatively thick peat, offered little attenuation to water draining toward the stream channel, and the source area for stream flow was relatively large. The duration of this high flow regime varied among hillsides due to variations in the width of the near-stream area, the gradient, length and inclination of hillslopes, and the water equivalent and melt rate of the snowpack. When the water table subsided into the lower peat layer, and discharge from inter-hummock channels decreased ( <0.1 m 3 d -1 ), the runoff source area was relatively small. Under this condition, if drainage into the near-stream area increased, the lateral expansion of the runoff source area would be delayed due to the relatively large storage capacity near the stream.