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TitleApplication limits of the interpretation of near-surface temperature time series to assess groundwater recharge
AuthorGosselin, J S; Rivard, C; Martel, R; Lefebvre, R
SourceJournal of Hydrology vol. 538, 2016 p. 96-108, https://doi.org/10.1016/j.jhydrol.2016.03.055
Year2016
Alt SeriesEarth Sciences Sector, Contribution Series 20160249
PublisherElsevier
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
Subjectshydrogeology; groundwater; groundwater flow; groundwater resources; groundwater movement; heat flow; groundwater temperatures; temperature; soil moisture; soil profiles; soils; ground temperatures; soil mechanics; groundwater recharge rates
Illustrationsschematic diagrams; formulae; tables; bar graphs; graphs
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
AbstractThe main objective of this study was to test the application limits of a groundwater recharge assessment technique based on the inversion of a vertical one-dimensional numerical model of advective-conductive heat transport, using temperature time series at three different depths (1, 3 and 5 m) in the unsaturated zone. For this purpose, several synthetic hourly datasets of subsurface temperatures, representing various weather, ground cover, and soil texture conditions, thus covering a wide range of groundwater recharge values, were produced with the vertical one-dimensional coupled heat and moisture transport simulator SHAW. Estimates of the vertical flux of water in the soil were then retrieved from these realistic temperature profiles using a simple one-dimensional numerical simulator of advective and conductive heat transport in the unsaturated zone that was developed as part of this study. The water flux was assumed constant on a weekly, monthly, semi-annual, and annual basis. From these vertical water flux estimates, annual (potential) groundwater recharge rates were then computed and results were compared to those calculated previously with SHAW to assess the accuracy of the method. Results showed that, under ideal conditions, it would be possible to estimate annual recharge rates that are above 200mm/y, with an acceptable error of less than 20 %. These 'ideal' conditions include the resolution of the water flux on a weekly basis, error-free temperature measurements below the soil freezing zone, and model parameter values (thermal conductivity and heat capacity of the soil) known a priori with no uncertainty. However, this work demonstrates that the accuracy of the method is highly sensitive to the uncertainty of the input model parameters of the numerical model used to carry out the inversion and to measurement errors of temperature time series. For the conditions represented in this study, these findings suggest that, despite the best modeling and field instrumentation practices, heat-based techniques for the assessment of diffuse groundwater recharge rates are likely not well suited for real field conditions, but could still represent a viable approach for applications carried out in engineered materials and under controlled conditions.
Summary(Plain Language Summary, not published)
The main objective of this study was to test the application limits of a groundwater recharge assessment technique based on subsurface temperature time series collected at different depths in the unsaturated zone for various climates representatives of different regions in Canada. This was done with numerical modeling using a vertical one-dimensional coupled heat and moisture transport simulator. Results show that, under ideal conditions, it would be possible to estimate annual recharge rates when the latter is above 200mm/y, with an acceptable error of less than 20 %. However, the error increases rapidly beyond the recharge value itself when measurement errors of soil temperatures and model parameter uncertainty are taken into account. This indicates that heat-based techniques for the assessment of diffuse groundwater recharge rates are likely not well suited for real field conditions. They could, nonetheless, represent an interesting approach for applications carried out in engineered materials and under controlled conditions such as in laboratories.
GEOSCAN ID299404