Abstract
Abstract. The groundwater response to Earth tides and atmospheric pressure changes can be used to understand subsurface processes and estimate hydraulic and hydro-mechanical properties. We develop a generalised frequency domain approach to disentangle the impacts of Earth and atmospheric tides on groundwater level responses. By considering the complex harmonic properties of the signal, we improve upon a previous method for quantifying barometric efficiency (BE), while simultaneously assessing system confinement and estimating hydraulic conductivity and specific storage. We demonstrate and validate this novel approach using an example barometric and groundwater pressure record with strong Earth tide influences. Our method enables improved and rapid assessment of subsurface processes and properties using standard pressure measurements.
Highlights
The groundwater response to barometric pressure and gravity changes caused by Earth tides has long been observed and is a powerful yet underutilised tool to passively characterise subsurface systems (McMillan et al, 2019)
We present a frequency domain method to disentangle the groundwater response to Earth and atmospheric tides
Our novel approach exploits the fact that the complex harmonic components can be determined for each variable, i.e. barometric pressure, borehole water level and Earth tides from which subsurface flow direction in response to stresses allows the inference of confinement, estimation of barometric efficiency (BE), hydraulic conductivity and specific storage
Summary
The groundwater response to barometric pressure and gravity changes caused by Earth tides has long been observed and is a powerful yet underutilised tool to passively characterise subsurface systems (McMillan et al, 2019). The method by Acworth et al (2016) is based on the assumption that the borehole water level is representative of subsurface pore pressure, i.e. there is an instantaneous and undamped response Under such conditions, only the phase difference between the theoretical Earth and atmospheric tide drivers is required to correct the groundwater response amplitude. Sci., 24, 6033–6046, 2020 instantaneous and undamped groundwater response to Earth tides is not always a given and phase delays must be considered when quantifying BES2 from the groundwater response to atmospheric tides In this technical note, we generalise the method by Acworth et al (2016) by more completely disentangling the groundwater response to EATs in the frequency domain. We illustrate the interpretative value of this new approach, using an example atmospheric pressure and borehole water level record that is strongly affected by EATs, followed by a verification of our results, using the well’s barometric response function calculated in the time domain
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