Experimental evaluation of the applicability of phase, amplitude, and combined methods to determine water flux and thermal diffusivity from temperature time series using VFLUX 2

Abstract

Vertical fluid exchange between surface water and groundwater can be estimated using diurnal signals from temperature time series methods based on amplitude ratios (A r), phase shifts (Δϕ), or combined use of both (A r Δϕ). The A r , Δϕ, and A r Δϕ methods are typically applied in conditions where one or more of their underlying assumptions are violated, and the reliability of the various methods in response to non-ideal conditions is unclear. Additionally, A r Δϕ methods offer the ability to estimate thermal diffusivity (κ e) without assuming any thermal parameters, although the value of such output has not been broadly tested The A r , Δϕ, and A r Δϕ methods are tested under non-steady, 1D flows in sand column experiments, and multi-dimensional flows in heterogeneous media in numerical modeling experiments. Results show that, in non-steady flow conditions, estimated κ e values outside of a plausible range for streambed materials (0.028 to 0.180 m 2 d-1) coincide with time periods with erroneous flux estimates. In heterogeneous media, sudden changes of κ e with depth also coincide with erroneous flux estimates. When (known) fluxes are variable in time, poor identification of Δϕ leads to poor flux estimates from Δϕ and A r Δϕ methods. However, when fluxes are steady, or near zero, A r Δϕ methods provide the most accurate flux estimates. This comparison of A r , Δϕ and A r Δϕ methods under non-ideal conditions provides guidance on their use. In this study, A r Δϕ methods have been coded into a new version of VFLUX, allowing users easy access to recent advances in heat tracing.

Influence of groundwater on distribution of dwarf wedgemussels (<i>Alasmidonta heterodon</i>) in the upper reaches of the Delaware River, northeastern USA

“…Point-scale physical methods, such as in-river piezometers and seepage meters , indicate the direction and magnitude of flow across the sediment-water interface at specific locations. Streambed vertical temperature profiles can also be used to determine seepage direction and rate, and can extend point-in-time measurements of water flux to month-long time series of sub-daily flux estimates using automated analytical (e.g., Irvine et al, 2015;Gordon et al, 2012) and numerical (e.g., Koch et al, 2015;Voytek et al, 2014) 1-D models. Other temperature-based methods can be used to separate groundwater discharge from superimposed hyporheic flow.…”

Heat: An Overlooked Tool in the Practicing Hydrogeologist's Toolbox

“…While we acknowlege that there are generally more scientific papers being published on many topics every year, Figure 3 demonstrates the sharp resurgance in academic interest on this topic following the review paper by Anderson (2005). These concepts have been built into free, downloadable software packages, such as VFLUX 2 (Irvine et al 2015) that use analytical approaches or numerical solutions such as those applied in 1DTempPro (Koch et al 2016). Most post-2005 academic studies that focused on the use of heat as a groundwater tracer were groundwater-surface water interaction studies that relied on temperaturetime approaches (Figure 2c and 2d).…”

Heat as a groundwater tracer in shallow and deep heterogeneous media: Analytical solution, spreadsheet tool, and field applications

“…First the domain was divided into the two distinct layers as indicated by the core as well as the sharp break in the temperature profile at 0.16 m below the streambed surface (Figure b). The thermal diffusivity of these two sediments was estimated based on the diel signal propagation using a procedure in VFLUX2 (Irvine, Lautz, Briggs, Gordon, & McKenzie, ) that is discussed in detail by Irvine, Briggs, Cartwright, Scruggs and Lautz (). Along the principal (0.16‐m mud over sand) HRTS profile, the diel signal was fully extinguished below sensor precision before the sand layer.…”