University of California Water Resources Center
Investigation of Groundwater Flow in Foothill and Mountain regions using Heat Flow measurements
- Author(s): Fogg, Graham E.
- Trask, James C
- et al.
A field and model investigation has been performed to assess the potential of
subsurface temperature (T) measurements for tracing groundwater flow in montane areas.
Field measurements included monitoring of soil T at numerous sites and measurement of
T-profiles in many wells and boreholes. Field data collection for thermal tracing of
groundwater flow is inexpensive and easy to perform relative to standard geophysical
techniques for groundwater flow characterization, given wells that are accessible for Tprofile
measurement. Modeling investigations include development of a novel,
conceptually simple ‘black box’ subsurface thermal energy balance approach. This robust
model approach can be used together with T-profile data to bracket the rate of mountainfront
Results of the soil T monitoring investigation show a wide range in summer and
mean annual soil T between different soil sites. Factors governing the observed inter-site
differences in soil T were identified. A model for spatial variability in mean soil T was
developed, showing the feasibility of creating maps of mean surface T in the Sierra
Nevada using standard GIS land surface attributes. Accurate knowledge of surface T is
needed in modeling subsurface heat and water flow, to distinguish spatial changes in T
due to groundwater flow from those due to heterogeneity in surface T. T-profiles
measured in the Tahoe Basin region indicate that there are substantial areal differences in
the rate of high elevation deep bedrock groundwater recharge, and in valley bedrock
discharge. Surface T and T-profile measurements together are shown to be useful in
defining valley basin-fill aquifer recharge sources. Subsurface heat flow patterns are
altered in distinct ways, as reflected in T-profiles, by recharge into the top (soil
percolation down to water table), sides (mountain-front recharge) and bottom (mountainblock
recharge) of montane valley basin-fill aquifers.