Subsurface drainage from hummock-covered hillslopes in the Arctic tundra

In the Arctic tundra, subsurface drainage occurs predominantly through the saturated zone within the layer of peat that mantles the hillslopes. In pla n view, the peat cover is fragmented into a network of channels due to the presence of mineral earth hummocks. In cross section, the physical and hydr aulic properties of the peat vary with depth and the water transmission cha racteristics (e.g. hydraulic conductivity) of the upper profile differ dist inctly from those of the lower. Water flow through the peat is laminar, the refore the friction factor (f) and the Reynolds number (N-R) are inversely related. Average values for the coefficient C of the relation f = C/N-R, va ry from similar to 300 near the surface to similar to 14,500 at depth. This large difference in C confirms that the larger-diameter soil pores of the living vegetation and lightly decomposed peat near the surface offer much l ess resistance to water motion than the finer-grained peat deeper in the pr ofile. Also, the variability suggests that subsurface drainage is strongly affected by the position and thickness of the saturated zone within the pea t matrix. A first approximation for a model or simulation of the how regime may consider a peat profile with depth-varying, resistance properties in r espect to subsurface flow. (C) 2000 Elsevier Science B.V. All rights reserv ed.