Abstract
Abstract. Quantification of subsurface water fluxes based on the one dimensional solution to the heat transport equation depends on the accuracy of measured subsurface temperatures. The influence of temperature probe setup on the accuracy of vertical water flux calculation was systematically evaluated in this experimental study. Four temperature probe setups were installed into a sand box experiment to measure temporal highly resolved vertical temperature profiles under controlled water fluxes in the range of ±1.3 m d−1. Pass band filtering provided amplitude differences and phase shifts of the diurnal temperature signal varying with depth depending on water flux. Amplitude ratios of setups directly installed into the saturated sediment significantly varied with sand box hydraulic gradients. Amplitude ratios provided an accurate basis for the analytical calculation of water flow velocities, which matched measured flow velocities. Calculated flow velocities were sensitive to thermal properties of saturated sediment and to temperature sensor spacing, but insensitive to thermal dispersivity equal to solute dispersivity. Amplitude ratios of temperature probe setups indirectly installed into piezometer pipes were influenced by thermal exchange processes within the pipes and significantly varied with water flux direction only. Temperature time lags of small sensor distances of all setups were found to be insensitive to vertical water flux.
Highlights
Understanding surface water-groundwater exchange flux is of prime importance for understanding saturated sediment biogeochemistry and hydroecology (Krause et al, 2011; Sophocleous, 2002; Boulton et al, 1998)
It was visually checked whether or not the 95 % confidence intervals of each median overlap. In case they do not overlap, the amplitude ratios and the time lags occurring for each h are seen as significantly different from each other at the 5 % significance level and are regarded to be sensitive to water flux. Based on this amplitude ratio and time lag sensitivity to different magnitudes of water flux, we evaluated whether subsurface temperature patterns provide a sufficient basis for analytical, temperature-based water flux calculations
The results show that vSediment and velocities based on MLTS derived amplitude ratios (vMLTS) were nearly identical, having low deviations for upward flow directions, www.hydrol-earth-syst-sci.net/15/3495/2011/
Summary
Understanding surface water-groundwater exchange flux is of prime importance for understanding saturated sediment biogeochemistry and hydroecology (Krause et al, 2011; Sophocleous, 2002; Boulton et al, 1998). The occurrence of heat in shallow hydrologic river-aquifer systems and its continuous exchange between surface water, underlying streambed sediments and adjacent groundwater, result in temperature profiles or subsurface temperature variations. These temperature variations can be recorded by single temperature sensors, as thermocouples and resistance thermometers at individual points (Keery et al, 2007; Hatch et al, 2006), by fibre-optic distributed temperature sensors for providing high resolution lateral patterns (Taylor et al, 2009), or continuous vertical profiles (Vogt et al, 2010) and used for quantifying the water exchange flux. Specific to field data availability and analytical solutions data requirements, they were applied in several case studies to evaluate temperature profiles (e.g. Constantz et al, 2003; Schmidt et al, 2006, 2007; Anibas et al, 2011) or temperature time series
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