scholarly journals Unsaturated Flow Influences the Response of Leaky Aquifer to Earth Tides

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 3) ◽  
Author(s):  
Ai-Yu Zhu
Keyword(s):  
Unsaturated Flow ◽  
Amplitude Ratio ◽  
Earth Tide ◽  
Ground Surface ◽  
Unconfined Aquifer ◽  
Earth Tides ◽  
Groundwater System ◽  
Free Drainage ◽  
Leaky Aquifer ◽  
Tidal Response

Abstract Most studies about the tidal response of leaky aquifers have treated the layered groundwater system as a classical unconfined aquifer without unsaturated flow. However, a recent study has shown that the conventional hypothesis of free drainage of groundwater to the watertable may be defective and the unsaturated flow may strongly affect their tidal response. Hence, it is critical to examine if unsaturated flow may also affect the tidal response of a layered groundwater system. In this study, we apply two-dimensional multilayered numerical simulations to examine the tidal response of unsaturated flow in a leaky aquifer. The results show that unsaturated flow on the watertable may significantly affect the tidal response of deeply buried aquifers, and the thicker the unsaturated zone is, the greater influence on the groundwater response to earth tide would be. Besides, a dimensionless quality ω∗ is introduced to estimate the effect of the unsaturated flow. When ω∗>10−0.5, the effect of the unsaturated flow on the tidal response of the water level is evidently; otherwise, the effect can be neglected. We then apply the numerical model to interpret the tidal response of a well installed in Lijiang, Yunnan province, China. It perfectly explains that the phase shift and amplitude ratio, respectively, decrease and increase exponentially when the watertable is below the ground surface. This study emphasizes the necessity of considering unsaturated flow in the multilayered model to improve the accuracy of predicting the permeability of the leaky aquifer.

scholarly journals Various far-field hydrological responses during 2015 Gorkha earthquake at two distant wells

2020 ◽  
Author(s):  
Xudong Huang ◽  
Yu Zhang
Keyword(s):  
Water Level ◽  
Seismic Waves ◽  
Amplitude Ratio ◽  
Unconfined Aquifer ◽  
Water Levels ◽  
Earth Tides ◽  
Tibet Plateau ◽  
Far Field ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake

Abstract Aquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic changes of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an occurrence in the vertical permeability of a switched semiconfined aquifer in the D22 well, or an enhancement unconfined aquifer in the LJ well . Using the continuous transmissivity monitoring, we show that the possible coseismic response for about 10 days and instant healing after 10 days to the earthquake. Thus, the dynamic shaking during the Gorkha earthquake may have caused the short term aquifer responses by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

Identification of the Earth Tide’s Influences and its Main Influencing-Components on Groundwater Level in an Unconfined-Aquifer

2020 ◽  
Author(s):  
Jian Guo ◽  
Mo Xu ◽  
Haoxin Shi ◽  
Jianhong Ge
Keyword(s):  
Groundwater Level ◽  
Cross Correlation ◽  
Earth Tide ◽  
Unconfined Aquifer ◽  
Earth Tides ◽  
Groundwater Levels ◽  
Monitoring Well ◽  
The Earth ◽  
Cross Correlation Analysis ◽  
Periodic Changes

<p>It is well known that various kinds of factors are causing the fluctuation of the groundwater level. The influence of earth tide on groundwater is first observed in confined-aquifer, while in unconfined-aquifer, understanding the influence of earth tide on the micro-fluctuation of the water level is crucial for obtaining key geo-hydrological parameters of the aquifer. In this study, the groundwater level of a monitoring well in Kualiangzi Village, Zhongjiang County, Deyang, as well as the data of local earth tides and rainfall were collected. And then the identification of the earth tide’s influences and its main influencing-components on groundwater level were studied by means of spectral analysis, cross-correlation analysis and harmonic analysis. The results show that the local groundwater levels are featured periodic changes of 1-day, 1/2 day and 1/3 day, which are corresponded to the earth tide. Moreover, the amplitude of the groundwater levels are negatively correlated with the earth tide, and there is no obvious hysteresis between them. The main influencing-components of earth tide are K1 diurnal wave and S2 semidiurnal wave.</p>

Fundamental statistical techniques for the analysis of earth tides

1971 ◽  
Vol 61 (1) ◽  
pp. 203-215
Author(s):  
Cheh Pan
Keyword(s):  
Computer Technology ◽  
Earth Tide ◽  
Power Spectra ◽  
Correlation Coefficients ◽  
Earth Tides ◽  
Statistical Techniques ◽  
The Earth ◽  
Tidal Data ◽  
Instrumental Drift ◽  
Phase Differences

abstract Recent advances in instrumentation, digital computer technology and mathematical theory promote the error analysis of Earth-tide data. Various statistical techniques developed and used in other fields are applicable in the study of Earth tides, and the accuracy of the Earth's rigidity constants determined from the tides will be greatly improved with the help of these techniques. The fundamentals of the statistical techniques of autocorrelation, crosscorrelation, convolution, statistical means, bandpass filtering, correlation coefficients, power spectra, coherency and equalization are described, and their principal applications in the Earth-tide analysis summarized. Examples of effective application of these techniques in the elimination of the errors in the tidal data such as those introduced from instrumental drift, phase differences between the observed and predicted tides, etc. are discussed. This work is an attempt to introduce statistical analysis into the Earth-tide study.

scholarly journals Tidal Response of Groundwater in a Leaky Aquifer—Application to Oklahoma

2018 ◽  
Vol 54 (10) ◽  
pp. 8019-8033 ◽  
Author(s):  
Chi‐Yuen Wang ◽  
Mai‐Linh Doan ◽  
Lian Xue ◽  
Andrew J. Barbour
Keyword(s):  
Leaky Aquifer ◽  
Tidal Response

scholarly journals Saturated–unsaturated flow in a compressible leaky-unconfined aquifer

2012 ◽  
Vol 42 ◽  
pp. 62-70 ◽  
Author(s):  
Phoolendra K. Mishra ◽  
Velimir V. Vesselinov ◽  
Kristopher L. Kuhlman
Keyword(s):  
Unsaturated Flow ◽  
Unconfined Aquifer

scholarly journals The saline Interface of a Shallow Unconfined Aquifer, Rangitikei Delta

2021 ◽  
Author(s):  
◽  
Desiree S A Craig
Keyword(s):  
Salt Marsh ◽  
River Estuary ◽  
Shallow Groundwater ◽  
Cumulative Effect ◽  
High Volume ◽  
Unconfined Aquifer ◽  
Saline Intrusion ◽  
Groundwater System ◽  
The North ◽  
Groundwater Aquifer

<p>The coastal communities of Tangimoana and Scott's Ferry have a long history of using shallow groundwater bores. The cumulative effect of pumping over decades could influence the saline interface given the close proximity of the communities to the seashore and river estuary. It is important to quantify the effects of pumping on both the shallow groundwater system and the dynamics of the saline interface. This is necessary to protect the groundwater system against saline intrusion especially given the increasing number of high volume groundwater consents to support dairying. Resistivity soundings and traverses, coupled with chemical analyses of groundwater samples, were found to be an effective method for defining the saline interface of the shallow groundwater aquifer under the Rangitikei delta. The saline interface extends from the salt marsh to beneath the farmland north of Tangimoana. The interface is a zone of diffusion with freshwater and brackish water mixing from the estuary. The interface is currently located on the outskirts of Tangimoana, and it is likely to extend beneath the township. The infiltration of brackish surface waters into sediments of the salt marsh form a surficial mixing zone that decreases with distance from the salt marsh. There is no indication of salinity in the area to the north of the Rangitikei delta. This area is most at risk of contamination from saline intrusion because of high volume groundwater abstractions, even though these abstractions are from deeper aquifers. The shallow groundwater beneath Tangimoana showed high concentrations of Ca and HCO3 ions. This may be a result of carbonate dissolution, which can occur when saline and freshwater mix. This creates groundwater that is under-saturated with calcium. The mixing water dissolves carbonates and increases the concentrations of Ca and HCO3. The major source of sodium and chloride was likely rainwater with evaporated solutes from seawater. The saline interface near Tangimoana appears to be relatively static, but the estuary and salt marsh are areas of low relief. There are preferential flows paths across the salt marsh to the farmland. These factors make the shallow groundwater in the Rangitikei delta vulnerable to saline intrusion.</p>

scholarly journals Relevance of topographic control on hydrogeological properties of the weathered granite gneiss aquifer in watershed perspective -- Usri sub-basin, Giridih, India

2020 ◽  
Author(s):  
Ashok Kumar
Keyword(s):  
Water Table ◽  
Geographical Area ◽  
Ground Surface ◽  
Granite Gneiss ◽  
Unconfined Aquifer ◽  
Aquifer System ◽  
Northern Margin ◽  
Topographic Features ◽  
Basin Water ◽  
Basement Surface

Usri, a southward sloping fourth order drainage sub-basin of Barakar river, is located in the northern margin of Chhotanagpur plateau, Giridih, India. Gently sloping undulating landforms devoid of hills and outcrops is main characteristics of this sub-basin. Topographic elevation varies between 310 to 390 m MSL. Geographically it is located between lat 24.38° N to 24.54° N long and 86.07° E and 86.28° E longitudes. Thick weathered horizon developed over homogenous Archean granite-gneiss is the principal unconfined aquifer system. Basement topographic (weathering depth) and water table have been correlated with the surface topographic features (landforms). Presence of considerably thick weathered horizons, devoid of rock exposures, regional uniformity in geomorphic characters and its location at fringe of plateau provides favorable condition for correlation of surface topography with basement topography and water table. It has been observed that basement surface is replica of ground surface only in regional or watershed perspective with reference to common datum. The basement surface is not always exact replica of ground surface at micro watershed scale. In many cases, basement surface is reverse of ground surface. The depth basement has remained constant along the basin water-divide situated near the margin of the plateau. The depth of basement (weathered horizon) is higher in upper reaches than lower reaches on the micro water-divides (upland) as well as in the drainage depressions (channels) within the sub-basin. The upper reaches of the sub-basin mainly along the basin water-divide has better groundwater prospects than lower reaches. There is no definite trend of water table with respect to ground and basement topography. Many places water table is shallow on the micro water-divides (upland) and deep in drainage depressions (channels). The established correlations are likely to be applicable in the other geographical area where similar watershed and geological characteristics exits.

scholarly journals ANALYSIS OF THE PRINCIPAL CONSTITUENTS OF SOLID EARTH TIDES ESTIMATED WITH GRAVIMETRIC AND GNSS DATA IN MANAUS AND BRASÍLIA

2019 ◽  
Vol 37 (1) ◽  
pp. 11
Author(s):  
Mário A. de Abreu ◽  
Giuliano S. Marotta ◽  
Lavoisiane Ferreira ◽  
Denizar Blitzkow ◽  
Ana C. O. C. de Matos ◽  
...  
Keyword(s):  
Time Series ◽  
Solid Earth ◽  
Earth Tide ◽  
Earth Tides ◽  
Data Series ◽  
Long Period ◽  
Solid Earth Tides ◽  
Gravimetric Data ◽  
Time Required ◽  
Solid Earth Tide

ABSTRACT. Solid Earth tide is the periodic displacement due to the tidal force. This effect is present in all geodesic and geophysical observations and should be eliminated when high accuracy surveying is required. It is necessary to determine the amplitudes and phases of the harmonic constituents to estimate the terrestrial tide effect magnitude. This article presents a methodology for estimating and analyzing the amplitudes and phases of the solid Earth tide principal constituents from gravimetric/GNSS observations. The methodology was applied to data collected in the Manaus/AM and Brasília/DF stations, Brazil, to determine the amplitude and phase values for the long period, monthly, diurnal and semidiurnal constituents, besides determining the time required for the convergence of the estimated constituent values. The estimated amplitude and phase values, using gravimetric data, converged between the 2nd and 6th months of the time series. For the positioning observations, the constituents values converged between the 2nd and 17th month of the data series, except for the long period constituent, which requires a longer time series to obtain satisfactory values for both methods. The results show that the solid Earth tide constituents were better estimated by the gravimetric data compared to the positioning data considering the series analyzed.Keywords: gravimetry, GNSS, solid Earth tide, tidal constituents.RESUMO. Maré terrestre é o deslocamento periódico decorrente da força de maré. Este é um efeito que deve ser eliminado quando se deseja realizar levantamentos nos quais é necessária alta acurácia tanto em observações geodésicas quanto geofísicas. Para estimar o efeito de maré terrestre deve-se determinar as amplitudes e fases de suas componentes harmônicas. Este artigo apresenta uma metodologia para a estimativa das amplitudes e fases das principais componentes de maré terrestre, a partir de observações gravimétricas/GNSS. A metodologia foi aplicada a dados coletados em estações instaladas em Manaus/AM e Brasília/DF, Brasil, resultando na determinação dos valores de amplitude e fase para componentes de longo período, mensais, diurnas e semidiurnas, além da análise da convergência dos valores estimados para estas componentes. As amplitudes e fases calculadas, utilizando dados gravimétricos, convergiram entre o 2_ e o 6_ mês analisados, enquanto para os dados de posicionamento a convergência ocorreu entre o 2_ e o 17_ mês observado, com exceção da componente de longo período, que não pôde ser determinada em ambos os métodos. Para o período analisado, as componentes de maré terrestre foram melhor estimadas utilizando dados gravimétricos, se comparadas aos resultados obtidos com dados de posicionamento.Palavras-chave: gravimetria, GNSS, maré terrestre, componentes de maré.

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.

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