Disentangling the groundwater response to Earth and atmospheric tides reveals subsurface processes and properties

2020 ◽  
Author(s):  
Gabriel Rau ◽  
Timothy McMillan ◽  
Mark Cuthbert ◽  
Martin Andersen ◽  
Wendy Timms ◽  
...  
Keyword(s):  
Water Level ◽  
Amplitude Ratio ◽  
Atmospheric Tides ◽  
Frequency Domain Method ◽  
Specific Storage ◽  
Strain Anisotropy ◽  
Geomechanical Properties ◽  
Groundwater Response ◽  
Borehole Water ◽  
Harmonic Components

<p>In situ quantification of subsurface hydro-geomechanical properties is challenging and requires significant effort. Evolving research illustrates that subtle harmonic components in groundwater head measurements caused by Earth and atmospheric tides can be utilised to explore groundwater systems with little effort compared to traditional investigations. One long standing problem has been that, for dominant tidal components, Earth and atmospheric tides occur at the same frequency which prevents the use of the groundwater response to their individual forcing to infer subsurface properties. While Acworth et al. (2016) offered a way forward, their approach has assumptions that limit the applicability. Here, we illustrate an extended method that disentangles the borehole water level response and attributes magnitude and phase to their individual drivers. As a result, we obtain individual changes in harmonic properties of the drivers and their groundwater response (amplitude ratio and phase shift) using borehole water level records from different locations. In conjunction with groundwater flow and poroelastic theory, these properties can be used to infer the state of confinement, quantify specific storage and hydraulic conductivity as well as barometric efficiency of the formation. Further, because the stresses imposed by Earth and atmospheric tides are volumetric and uniaxial, respectively, their individual responses can be used to reveal strain anisotropy. Our new approach is passive, i.e. it only requires the measurements of atmospheric and groundwater pressure records, and can provide further insight into subsurface processes and properties using information hidden in standard pressure records.</p><p> </p><p>Acworth, R. I., Halloran, L. J. S., Rau, G. C., Cuthbert, M. O., and Bernardi, T. L. ( 2016), An objective frequency domain method for quantifying confined aquifer compressible storage using Earth and atmospheric tides, Geophys. Res. Lett., 43, 11,671–11,678, doi:10.1002/2016GL071328.</p>

scholarly journals Technical Note: Disentangling the groundwater response to Earth and atmospheric tides to improve subsurface characterisation

2020 ◽  
Author(s):  
Gabriel C. Rau ◽  
Mark O. Cuthbert ◽  
R. Ian Acworth ◽  
Philipp Blum
Keyword(s):  
Rapid Assessment ◽  
Earth Tide ◽  
Technical Note ◽  
Previous Method ◽  
Earth Tides ◽  
Atmospheric Tides ◽  
Specific Storage ◽  
Novel Approach ◽  
Groundwater Response ◽  
Pressure Record

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 estimating barometric efficiency (BE) estimation while simultaneously assessing system confinement and estimating hydraulic conductivity as well as specific storage. We demonstrate and validate the 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.

scholarly journals In-situ estimation of subsurface hydro-geomechanical properties using the groundwater response to Earth and atmospheric tides

2021 ◽  
Author(s):  
Timothy C. McMillan ◽  
Martin S. Andersen ◽  
Wendy A. Timms ◽  
Gabriel C. Rau
Keyword(s):  
Water Levels ◽  
Atmospheric Tides ◽  
New Approach ◽  
Geomechanical Properties ◽  
Groundwater Response ◽  
In Situ Conditions ◽  
The Impact ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

Abstract. Subsurface hydro-geomechanical properties crucially underpin the management of Earth's resources, yet they are predominantly measured on core-samples in the laboratory while little is known about the representativeness of in-situ conditions. The impact of Earth and atmospheric tides on borehole water levels are ubiquitous and can be used to characterise the subsurface. We illustrate that disentangling the groundwater response to Earth and atmospheric tidal forces in conjunction with hydraulic and linear poroelastic theories leads to a complete determination of the whole hydro-geomechanical parameter space for unconsolidated systems. Further, the characterisation of consolidated systems is possible when using literature estimates of the grain compressibility. While previous field investigations have assumed a Poisson's ratio from literature values, our new approach allows for its estimation under in-situ field conditions. We apply this method to water level and barometric pressure records from four field sites with contrasting hydrogeology. Estimated hydro-geomechanical properties (e.g. specific storage, hydraulic conductivity, porosity, shear-, Young's- and bulk- moduli, Skempton's and Biot-Willis coefficients and undrained/drained Poisson's ratios) are comparable to values reported in the literature, except for consistently negative drained Poisson's ratios which are surprising. Our results reveal an anisotropic response to strain, which is expected for a heterogeneous (layered) lithological profile. Closer analysis reveals that negative Poisson's ratios can be explained by differing in-situ conditions to those from typical laboratory core tests and the small strains generated by Earth and atmospheric tides. Our new approach can be used to passively, and therefore cost-effectively, estimate subsurface hydro-geomechanical properties representative of in-situ conditions. Our method can be used to improve our understanding of the relationship between geological heterogeneity and geomechanical behaviour.

scholarly journals Technical note: Disentangling the groundwater response to Earth and atmospheric tides to improve subsurface characterisation

2020 ◽  
Vol 24 (12) ◽  
pp. 6033-6046
Author(s):  
Gabriel C. Rau ◽  
Mark O. Cuthbert ◽  
R. Ian Acworth ◽  
Philipp Blum
Keyword(s):  
Rapid Assessment ◽  
Earth Tide ◽  
Technical Note ◽  
Previous Method ◽  
Earth Tides ◽  
Atmospheric Tides ◽  
Specific Storage ◽  
Novel Approach ◽  
Groundwater Response ◽  
Pressure Record

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.

A new Python package to estimate hydraulic and poroelastic groundwater properties using standard pressure records

2021 ◽  
Author(s):  
Gabriel Rau ◽  
Daniel Schweizer ◽  
Chris Turnadge ◽  
Philipp Blum ◽  
Todd Rasmussen
Keyword(s):  
Earth Tide ◽  
Barometric Pressure ◽  
Earth Tides ◽  
Specific Storage ◽  
Geomechanical Properties ◽  
Groundwater Response ◽  
Barometric Efficiency ◽  
Standard Pressure ◽  
Pressure Changes ◽  
Python Package

<p>Determining subsurface hydraulic and geomechanical properties crucially underpins groundwater resource investigation and management. While standard practice relies on active testing, passive approaches require less effort and cost but are underutilised. We present the new Python package named HydroGeoSines (HGS) which quantifies hydraulic and poroelastic subsurface properties using the groundwater response to natural forces (such as Earth tides and atmospheric pressure changes) embedded in standard measurements. All implemented methods are drawn from the peer-reviewed literature. The package includes basic handling of time series, such as joining and aligning records and handling gaps. HGS uses standard atmospheric and groundwater pressure records to estimate the Barometric Response Function (BRF) groundwater state of confinement, hydraulic conductivity, specific storage, barometric efficiency (BE) and porosity. If Earth tides are required, they can be calculated on-the-fly using the PyGTide package which is based on ETERNA and included. HGS allows easy compensation and correction of pressure or hydraulic heads from barometric pressure or Earth tide influences. Further, HGS includes import from and export to common data formats as well as visualisation of data and results. We demonstrate the use of HGS using example datasets from around the world. Since HGS unlocks sophisticated methods for use by anyone with Python skills, we anticipate that it will support subsurface investigations and add value to standard monitoring practice.</p>

Estimation of in-situ hydro-geomechanical properties using the groundwater responses to natural cyclical forcing

2021 ◽  
Author(s):  
Timothy McMillan ◽  
Gabriel Rau ◽  
Wendy Timms ◽  
Martin Andersen
Keyword(s):  
Land Surface ◽  
A Priori Estimate ◽  
Regulatory Compliance ◽  
Earth Tides ◽  
Atmospheric Tides ◽  
Specific Storage ◽  
Low Frequencies ◽  
Geomechanical Properties ◽  
Wide Range

<p>Earth and atmospheric tides are prevalent across the land-surface and provide natural forcing to characterise the hydro-geomechanical confined subsurface by using their groundwater response. Since tides are harmonic, their individual influences on the pressure head can be separated into complex components containing level or pressure magnitudes and phases. The approximated planar strain from Earth tides, and the uniaxial loading from atmospheric tides, allow the estimation of a wide range of values based on hydraulic and poroelastic relationships. With recent research advances, tidal analysis can be used to estimate hydro-geomechanical properties including specific storage, hydraulic conductivity, porosity, shear, Young’s and Bulk moduli, Skempton’s and Biot-Willis coefficients and undrained/drained Poisson’s ratios. This approach does not require any assumption on mineral grain compressibility for unconsolidated systems. However, consolidated materials currently require an a priori estimate of grain compressibility. We applied this method to pressure measurements from different geological settings. The estimated hydro-geomechanical properties comply with theoretically expected values except for Poisson’s ratio, which differs from laboratory values due to differing confining pressures, and comparatively low frequencies of the Earth and Atmospheric tide signals. However, these estimated values from in-situ data are likely more realistic of the natural hydrogeological response. We anticipate that, by developing methods that routinely can derive engineering geotechnical values through the monitoring of hydraulic head variations, the collection of groundwater pressures will become a priority for large civic excavations or construction, such as mining, in addition to environmental studies and regulatory compliance.</p>

Interaction between water pressure in the basal drainage system and discharge from an Alpine glacier before and during a rainfall-induced subglacial hydrological event

1997 ◽  
Vol 24 ◽  
pp. 288-292 ◽  
Author(s):  
Andrew P. Barrett ◽  
David N. Collins
Keyword(s):  
Water Level ◽  
Water Pressure ◽  
Drainage System ◽  
Water Levels ◽  
Drainage Network ◽  
Alpine Glacier ◽  
Hydraulic Conditions ◽  
Borehole Water ◽  
Progressive Growth ◽  
Resultant Increase

Combined measurements of meltwater discharge from the portal and of water level in a borehole drilled to the bed of Findelengletscher, Switzerland, were obtained during the later part of the 1993 ablation season. A severe storm, lasting from 22 through 24 September, produced at least 130 mm of precipitation over the glacier, largely as rain. The combined hydrological records indicate periods during which the basal drainage system became constricted and water storage in the glacier increased, as well as phases of channel growth. During the storm, water pressure generally increased as water backed up in the drainage network. Abrupt, temporary falls in borehole water level were accompanied by pulses in portal discharge. On 24 September, whilst borehole water level continued to rise, water started to escape under pressure with a resultant increase in discharge. As the drainage network expanded, a large amount of debris was flushed from a wide area of the bed. Progressive growth in channel capacity as discharge increased enabled stored water to drain and borehole water level to fall rapidly. Possible relationships between observed borehole water levels and water pressures in subglacial channels are influenced by hydraulic conditions at the base of the hole, distance between the hole and a channel, and the nature of the substrate.

scholarly journals Estimation of hydraulic properties of subglacial till from ploughmeter measurements

1998 ◽  
Vol 44 (148) ◽  
pp. 517-522 ◽  
Author(s):  
Urs H. Fischer ◽  
Neal R. Iverson ◽  
Brian Hanson ◽  
Roger LeB. Hooke ◽  
Peter Jansson
Keyword(s):  
Water Level ◽  
Hydraulic Properties ◽  
Water Pressure ◽  
Inverse Correlation ◽  
Borehole Water ◽  
Potential Gradients ◽  
Glacial Tills ◽  
Basal Till ◽  
Range Of Values ◽  
Good Agreement

Abstract Force variations on a "ploughmeter" and fluctuations in subglacial water pressure have been measured in the same borehole at Storglaciaren, Sweden, to investigate hydraulic properties of the basal till layer. A strong inverse correlation of the pressure and force records, in conjunction with a significant lime lag between the two signals, suggests that pore-water pressures directly affect the strength of the till. Variations in sub-glacial water pressure result in potential gradients across the water till interlace at the bottom of the borehole that drive pressure waves downwards through the till layer when the borehole water level is high and back upwards when the water level is low. Analysis of the propagation velocity of this pressure wave indicates that the hydraulic diffusivity of Storglaciaren till is in the range 1.9−3.6 x 10−6m2s−1,in good agreement with estimates obtained in the laboratory. Hydraulic conductivity values associated with these difrusivities are between 10−9 and 10−8ms−1 and thus are well within the range of values for other glacial tills.

Interaction between water pressure in the basal drainage system and discharge from an Alpine glacier before and during a rainfall-induced subglacial hydrological event

1997 ◽  
Vol 24 ◽  
pp. 288-292 ◽  
Author(s):  
Andrew P. Barrett ◽  
David N. Collins
Keyword(s):  
Water Level ◽  
Water Pressure ◽  
Drainage System ◽  
Water Levels ◽  
Drainage Network ◽  
Alpine Glacier ◽  
Hydraulic Conditions ◽  
Borehole Water ◽  
Progressive Growth ◽  
Resultant Increase

Combined measurements of meltwater discharge from the portal and of water level in a borehole drilled to the bed of Findelengletscher, Switzerland, were obtained during the later part of the 1993 ablation season. A severe storm, lasting from 22 through 24 September, produced at least 130 mm of precipitation over the glacier, largely as rain. The combined hydrological records indicate periods during which the basal drainage system became constricted and water storage in the glacier increased, as well as phases of channel growth. During the storm, water pressure generally increased as water backed up in the drainage network. Abrupt, temporary falls in borehole water level were accompanied by pulses in portal discharge. On 24 September, whilst borehole water level continued to rise, water started to escape under pressure with a resultant increase in discharge. As the drainage network expanded, a large amount of debris was flushed from a wide area of the bed. Progressive growth in channel capacity as discharge increased enabled stored water to drain and borehole water level to fall rapidly. Possible relationships between observed borehole water levels and water pressures in subglacial channels are influenced by hydraulic conditions at the base of the hole, distance between the hole and a channel, and the nature of the substrate.

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