Possible Ambiguities in Subsurface Temperature Logs: Consideration of Ground-water Flow and Ground Surface Temperature Change

Subsurface temperature regimes can commonly be influenced by both ground-water flow in the saturated zone and ground surface temperature change. Both phenomena are widespread and one or the other may be unnoticed and/or unanticipated in various temperature logs. As a consequence, it is often difficult to determine the relative impact of the two phenomena on the temperature-depth data at a site. A number of models for ground-water flow, ground surface temperature change, and a combination of the two processes, are fitted to two example temperature logs showing characteristic nonlinearity. Examples of the possible impact of one phenomenon on the parameters calculated for the other phenomenon demonstrate the potential interactive influence. The analysis can be used to estimate potential uncertainties in calculations of ground-water flow and ground surface temperature change from subsurface temperature data, and therefore how interpretations of ground-water flow and ground surface warming might be affected. From the analysis presented the relative importance of the two phenomena may be further considered at different locations.