Groundwater temperatures during the winter in a forested basin

Vertical groundwater temperature profiles were measured in shallow (1-4 m) 5.08 cm diameter PVC wells at several sites within a small (0.47 km²), deciduous forested basin. All sites except one indicated that conduction was the predominant means of heat transport, as was evident by the profiles being close to linear with depth. At one site the temperature was uniform with depth, indicating that the advecting fluid kept the temperature profile shape from changing significantly during the entire fall or winter season.By the end of winter and just prior to snowmelt, groundwater temperatures at the 2 m depth ranged between 2 and 4.25degC, and were warmest at highest elevations in the basin. The spatial variability in groundwater temperatures at the 2 m depth at all sites was nearly 2degC throughout the winter period.The presence of a snow cover minimizes the infiltration of rainwater and subsequent advection of heat to the soil. A preliminary analysis of the data has shown that late in winter, the assumption of a steady state heat flux can be made. Vertical upward velocities in saturated soil regions on the order of 0.05 m/day were computed from a one-dimensional steady state heat and mass flow analysis using the temperature profiles.