Groundwater Head Fluctuations Research Articles

Significant coherence for groundwater and Rayleigh waves: Evidence in spectral response of groundwater level in Taiwan using 2011 Tohoku earthquake, Japan

Summary It was found that groundwater can be fluctuated by a variety of disturbances. For instance, seismic activity inducing the dilatation of earth can disturb groundwater level fluctuation as observed in groundwater wells. In this research, spectral analysis in the frequency domain was used to quantitatively evaluate coherence between groundwater head fluctuations and the ground motions recorded in Taiwan from a distant earthquake, the 2011 Tohoku earthquake in northern Honshu, Japan with magnitude of 9. The relationship between groundwater fluctuations and the decomposed ground motions of Rayleigh waves are clearly identified. By analyzing autospectral density, cross-spectral density, and resultant coherence for the seismograms and groundwater head, it was found that the Rayleigh waves dominated the groundwater fluctuations at period of about 21–32 s for six pair of groundwater and seismograms of broadband distributed around Taiwan; fluctuations of groundwater are highly coherent with the radial and vertical components of ground motions. Our analysis also shows the time from event to station for Rayleigh waves ranged from 780 to 900 s approximately. Wave parameter for seismic event to station of groundwater and seismograms were also identified as 3.0–3.5 km/s and 64–110 km for wave velocity and wave length, respectively. The relationship of groundwater fluctuations and ground motions induced by seismic activity become feasible to assess using spectral analysis.

The enhancing effect on tidal signals of a submarine spring connected to a semi-infinite confined aquifer

Submarine springs play an important role in submarine groundwater discharge (SGD). To investigate the effects of these springs on the propagation of tidal signals in coastal confined aquifers, this paper considers a general coastal aquifer system with a submarine spring on the seabed where the length of the aquifer's offshore extent is finite and its submarine outlet is covered by an impermeable outlet-capping. An approximate analytical solution is obtained for describing the tidal head fluctuations in the aquifer. Solution analyses indicate that the error of the approximate analytical solution is negligible when both distances from the spring hole to the coastline and to the submarine outlet-capping are much greater than the radius of the spring hole. Sensitivity tests are conducted to investigate the effects of hydraulic properties, tidal and spring geometric configuration parameters on the tidal signal propagation in the inland aquifer. For aquifers with infinite offshore length, or without submarine springs, existing solutions in the literature are obtained. The comparison of groundwater head fluctuations for the cases with and without a submarine spring demonstrate the enhancing effect of the submarine spring on tidal signal propagation in the inland aquifer. Three situations that fit our model assumptions are given for future potential applications. A hypothetical example is used to show the possibility of identifying a spring's location using the present analytical solution together with tidal signals observed from inland wells. Editor D. Koutsoyiannis; Associate editor Y. Guttmann Citation Xia, Y.Q., Li, H.L., Yang, Y., and Huang, W., 2012. Enhancing effect on tidal signals of a submarine spring related to a semi-infinite confined aquifer. Hydrological Sciences Journal, 57 (6), 1231–1248.

Analytical Study of Airflow Induced by Barometric Pressure and Groundwater Head Fluctuations in a Two-Layered Unsaturated Zone

A study on subsurface airflow plays a vital role in quantifying the effectiveness of natural attenuation of volatile organic compounds (VOCs) or in determining the need of engineering systems (e.g., soil vapor extraction of VOCs). Here, we present a new analytical solution for describing the subsurface airflow induced by barometric pressure and groundwater head fluctuations. The solution improves a previously published semi-analytical solution into a fully explicit expression and can save much computation efforts when it was used to estimate the soil permeability and porosity, which was demonstrated by a hypothetical example. If the groundwater head and barometric pressure fluctuations have the same frequency and the same order of magnitude for the amplitudes, each or the combination of both fluctuations will generate the air exchange volumes of the same order of magnitude through the ground surface. Particularly, the air exchange volume caused by the combined fluctuations increases with the upper layer's permeability and lower layer's porosity and decreases with the phase difference between these two fluctuations, fluctuation frequency, and the upper layer's thickness. The air exchange volume may decrease quickly to zero essentially when the upper layer's permeability decreases 10-fold and decrease fourfold to fivefold when the phase difference decreases from π to zero.

A generalized solution for groundwater head fluctuation in a tidal leaky aquifer system

A new analytical solution is developed for describing groundwater level fluctuations in a coupled leaky confined aquifer system which consists of an unconfined aquifer, confined aquifer, and an aquitard in between. The aquifer system has a tidal boundary at the seashore, a no flow boundary at remote inland side, and a confined aquifer extending under the sea and terminated with an outlet-capping. This new solution has shown to be a generalisation of most existing analytical solutions for a tidal aquifer system which includes single confined and leaky confined aquifers. In addition, the solution is used to explore the influences of the dimensionless leakance of the outlet-capping, the dimensionless hydraulic diffusivities, and the leakages of the inland and offshore aquitards on the head responses in the leaky confined aquifer.

A sensitivity analysis of tide-induced head fluctuations in coastal aquifers

Summary The response of coastal aquifers to sea-level fluctuations, notably tides, is known to contain much information about hydraulic parameters. We performed sensitivity analyses to assess how much, about what and where this information can be best obtained. It is well known that the response to harmonic fluctuations (and many harmonics can be superimposed to describe sea-level fluctuations) decreases exponentially with distance inland. The characteristic length of this decay is L c = DP / π , where D is hydraulic diffusivity and P is period. Maximum sensitivity is obtained for distances equal to L c , which is where maximum information would be obtained if the aquifer is treated as homogeneous. However, sensitivity depends not only on the problem dynamics, but also on parameterization. In fact, if heterogeneity is acknowledged by finely discretizing hydraulic conductivity, we find that connection to the sea (i.e. K near the coast) is what can be characterized best, while the most informative measurements are located at around 0.5 L c . Thin low conductivity zones near the coast lead to a stepwise decrease in the amplitude of groundwater head fluctuations. We find that the fluctuations are independent of buoyancy effects, so that they can be simulated by constant density codes. High information content and ease of use suggest that they should be helpful in characterizing the aquifer–sea connection, which is important for coastal aquifer protection against seawater intrusion.

Analytical modeling of saturated zone head response to evapotranspiration and river-stage fluctuations

Summary We investigate the response of the saturated zone (unconfined aquifer) to evapotranspiration (ET) flux at ground surface. We neglect fluid flow and storage in the unsaturated zone and treat ET as a sinusoidal forcing function at the watertable. The linearized kinematic condition is imposed at the watertable. Analytical solutions are developed for the case of flow in a domain of (a) semi-infinite extent to simulate response in a domain bounded by a river and (b) infinite lateral extent to simulate the response in a domain with no river boundaries. These solutions are fitted to observed groundwater head fluctuations recorded in observation wells at the Boise Hydrogeophysical Research Site in Idaho and the Larned Research Site in Kansas. Estimates of the amplitude of the ET flux, aquifer hydraulic conductivity, specific storage and specific yield are obtained and these compare well to published results from pumping tests conducted at the site. The field exercise is used to explore the potential for using groundwater head fluctuations to estimate ET and hydraulic parameters of unconfined aquifers.

Groundwater response to tidal fluctuation in a two-zone aquifer

Summary A coastal aquifer may consist of two zones of distinctly different hydraulic properties, with the coastal zone of limited width and the inland zone of infinite width. The analytical solutions for groundwater level response to tidal fluctuation in such a two-zone aquifer are derived and the underlying physical meanings are discussed. A dimensionless zone-contrast parameter r is introduced, which is controlled by ratio between the product of the transmissivity and storativity of the inland zone and that of the coastal zone. In the coastal zone, the amplitude of groundwater head fluctuation attenuates more quickly when r becomes greater. The amplitude declines exponentially with distance from the coastline, and the phase lag increases linearly only when r = 1. In the inland zone, however, the head fluctuation always exhibits an exponential attenuation of the amplitude and a linear increase of the phase lag for any value of r. Thus, the diffusivity of the inland zone can be readily assessed with measurements of fluctuation amplitudes or lags, as are frequently used when estimating aquifer parameters in homogeneous aquifers. Compared with Jacob (1950) solution for a semi-infinite homogeneous aquifer, the existence of the coastal zone reduces the amplitude in the inland zone by a spatially constant coefficient and increases the phase lag by a spatially constant shift. Inverse estimation of aquifer parameters are discussed based on the analytical solutions. The analytical solutions are used to estimate the aquifer parameters in a coastal two-zone aquifer located in the west part of Dongzhai Harbor, Hainan Province, China.

Tide-induced head fluctuations in a coastal aquifer: effects of the elastic storage and leakage of the submarine outlet-capping

This paper considers the tidal head fluctuations in a single coastal confined aquifer which extends under the sea for a certain distance. Its submarine outlet is covered by a silt-layer with properties dissimilar to the aquifer. Recently, Li et al. (2007) gave an analytical solution for such a system which neglected the effect of the elastic storage (specific storage) of the outlet-capping. This article presents an analytical solution which generalizes their work by incorporating the elastic storage of the outlet-capping. It is found that if the outlet-capping is thick enough in the horizontal direction, its elastic storage has a significant enhancing effect on the tidal head fluctuation. Ignoring this elastic storage will lead to significant errors in predicting the relationship of the head fluctuation and the aquifer hydrogeological properties. Quantitative analysis shows the effect of the elastic storage of the outlet-capping on the groundwater head fluctuation. Quantitative conditions are given under which the effect of this elastic storage on the aquifer’s tide-induced head fluctuation is negligible. Li, H.L., Li, G.Y., Chen, J.M., Boufadel, M.C. (2007) Tide-induced head fluctuations in a confined aquifer with sediment covering its outlet at the sea floor. [Fluctuations du niveau piezometrique induites par la maree dans un aquifere captif a decharge sous-marine.] Water Resour. Res 43, doi:10.1029/2005WR004724

Numerical simulation of the effect of the sloping submarine outlet-capping on tidal groundwater head fluctuation in confined coastal aquifers

The submarine outlet of a coastal confined aquifer is usually covered by less-permeable material such as silt and fine sand which forms a sloping or almost flat seabed. Previous analytical studies of the tide-induced head fluctuation usually assumed a vertical interface between the outlet-capping and the seawater and neglected the effects of the outlet-capping's slope. Here we conducted a series of numerical simulations to investigate the effect of the slope of the outlet-capping on the tide-induced head fluctuations in a coastal confined aquifer. The numerical simulations demonstrated that when the hydraulic diffusivity, slope and/or the outlet-capping leakance are large, the tidal loading effect is relatively weak and the leakance dominates. In this case the analytical solution applies. In general, the joint actions of the outlet-capping leakance and the tidal loading effects result in complicated, 2-dimensional flow in the aquifer near the shoreline. For aquifers with small hydraulic diffusivity, small slope and/or small outlet-capping leakance, the outlet acts approximately as a no-flow boundary condition and the tidal loading dominates. In this case, negative phase shifts (time-advance) may occur near the coastline. The study provides potential guide to infer the aquifer's submarine structure and parameter from tidal head fluctuation observations in inland wells.

The enhancing effect of the elastic storage of the seabed aquitard on the tide-induced groundwater head fluctuation in confined submarine aquifer systems

Summary This paper investigated the tide-induced head fluctuation in a coastal confined aquifer with an infinitely-extending semipermeable roof. The roof is overlain by an unconfined aquifer terminating at the coastline. Previous analytical studies ignored the effect of the elastic storage of the semipermeable roof. Our model incorporated this effect. The analytical solution indicated that the increase of the elastic storage of the offshore semipermeable roof may significantly enhance the tidal head fluctuation in the confined aquifer at the coastline. A threshold leakance exists in the sense that when the leakance is less than the threshold, the head fluctuation at the coastline will become insensitive to leakance and the roof can be regarded as impermeable. The threshold strongly depends on the roof’s elastic storage and decreases as the roof’s elastic storage increases, indicating that the roof’s leakage effect is significantly enhanced by the increase of the roof’s elastic storage.

Modeling Time Series of Ground Water Head Fluctuations Subjected to Multiple Stresses

The methods behind the predefined impulse response function in continuous time (PIRFICT) time series model are extended to cover more complex situations where multiple stresses influence ground water head fluctuations simultaneously. In comparison to autoregressive moving average (ARMA) time series models, the PIRFICT model is optimized for use on hydrologic problems. The objective of the paper is twofold. First, an approach is presented for handling multiple stresses in the model. Each stress has a specific parametric impulse response function. Appropriate impulse response functions for other stresses than precipitation are derived from analytical solutions of elementary hydrogeological problems. Furthermore, different stresses do not need to be connected in parallel in the model, as is the standard procedure in ARMA models. Second, general procedures are presented for modeling and interpretation of the results. The multiple-input PIRFICT model is applied to two real cases. In the first one, it is shown that this model can effectively decompose series of ground water head fluctuations into partial series, each representing the influence of an individual stress. The second application handles multiple observation wells. It is shown that elementary physical knowledge and the spatial coherence in the results of multiple wells in an area may be used to interpret and check the plausibility of the results. The methods presented can be used regardless of the hydrogeological setting. They are implemented in a computer package named Menyanthes (www.menyanthes.nl).

Tide‐induced groundwater head fluctuation in a coastal aquifer system with a submarine outcrop covered by a thin silt layer

AbstractWe present an analytical solution of groundwater head response to tidal fluctuation in a coastal multilayered aquifer system consisting of an unconfined aquifer, a leaky confined aquifer and a semi‐permeable layer between them. The submarine outcrop of the confined aquifer is covered by a thin silt layer. A mathematical model and the analytical solution of this model are given. The silt layer reduces the amplitude of the hydraulic head fluctuation by a constant factor, and shifts the phase by a positive constant (time lag), both of which depend on the leakances of the silt layer and the semi‐permeable layer. The time lag is less than 1·5 h and 3·0 h for semi‐diurnal and diurnal sea tides respectively. When the leakance of the semi‐permeable layer or the silt layer assumes certain special values, the solution becomes the existing solutions derived by previous researchers. The amplitude of the hydraulic head fluctuation in the confined aquifer increases with the leakance of the silt layer and decreases with the leakance of the semi‐permeable layer, whereas the phase shift of the fluctuation decreases with both of them. A hypothetical example shows that neglecting the silt layer may result in significant parameter estimation discrepancy between the amplitude attenuation and the time‐lag fittings. Copyright © 2007 John Wiley & Sons, Ltd.

Tide-induced groundwater head fluctuation in coastal multi-layered aquifer systems with a submarine outlet-capping

This paper considered the tide-induced head fluctuations in two coastal multi-layered aquifer systems. Model I comprises two semi-permeable layers and a confined aquifer between them. Model II is a four-layered aquifer system including an unconfined aquifer, an upper semi-permeable layer, a confined aquifer and a lower semi-permeable layer. In each model, the submarine outlet of the confined aquifer is covered with a skin layer (“outlet-capping”). Analytical solutions of the two models are derived. In both models, leakages of the semi-permeable layers decrease the tidal head fluctuations. The outlet-capping reduces the aquifer’s head fluctuation by a constant factor and shifts the phase by a positive constant. The solution to Model II explains the inconsistency between the relatively small lag time and the strong amplitude damping effect of the tidal head fluctuations reported by Trefry and Johnston [Ground Water 1998;36:427–33] near the Port Adelaide River, Australia.

Modelling tidal signals enhanced by a submarine spring in a coastal confined aquifer extending under the sea

Submarine springs discharge offshore groundwater from confined aquifers extending under the sea. The effects of these springs on the propagation of tidal oscillations in coastal confined aquifers are not known. This paper presents an approximate analytical solution of tidal head fluctuations in a confined aquifer with one submarine spring. The aquifer is assumed to extend in all directions infinitely. The spring is represented by a permeable round column on the seabed, which penetrates completely the impermeable layer overlying the confined aquifer. The error of the approximate solution is negligible if the distance from the spring to the coastline is much greater than the radius of the permeable column representing the spring. Through a hypothetical example, we demonstrate that it is possible to identify the spring’s location using tidal signals observed from inland wells. Tidal groundwater head fluctuations from three inland observation wells at least are needed to determine the 5 model parameters, including the location (2 parameters), the radius of the permeable column representing the spring, the diffusivity of the aquifer, and the tidal loading efficiency of the system.

Tidal influence on behaviour of a coastal aquifer adjacent to a low-relief estuary

The tidal influence on groundwater hydrodynamics, salt-water intrusion and submarine groundwater discharge from coastal/estuarine aquifers is poorly quantified for systems with a mildly sloping beach, in contrast to the case where a vertical beach face is assumed. We investigated the effect of beach slope for a coastal aquifer adjacent to a low-relief estuary, where industrial waste was emplaced over the aquifer. The waste was suspected to discharge leachate towards the estuary. Field observations at various locations showed that tidally induced groundwater head fluctuations were skewed temporally. Frequency analysis suggested that the fluctuation amplitudes decreased exponentially and the phase-lags increased linearly for the primary tidal signals as they propagated inland. Salinisation zones were observed in the bottom part of the estuary and near the beach surface. Flow and transport processes in a cross-section perpendicular to the estuary were simulated using SEAWAT-2000, which is capable of depicting density-dependent flow and multi-species transport. The simulations showed that the modelled water table fluctuations were in good agreement with the monitored data. Further simulations were conducted to gain insight into the effects of beach slope. In particular the limiting case of a vertical beach face was considered. The simulations showed that density difference and tidal forcing drive a more complex hydrodynamic pattern for the mildly sloping beach than the vertical beach, as well as a profound asymmetry in tidally induced water table fluctuations and enhanced salt-water intrusion. The simulation results also indicated that contaminant transport from the aquifer to the estuary was affected by the tide, where for the mildly sloping beach, the tide tended to intensify the vertical mass exchange in the vicinity of the shoreline.

Estimation of relative recharge sequence to groundwater with minimum entropy deconvolution

This study applies the minimum entropy deconvolution (MED) for the estimation of the sequential groundwater recharge rate. Groundwater recharge rates have conventionally been estimated as an average value over some period of time, e.g. annual or seasonal recharge rates. Such estimates however, are not suitable for the analysis of the dynamic sequential behavior of the groundwater head fluctuation. If the sequential groundwater recharge rate is obtained, numerical groundwater models can be effectively applied to evaluate the effect of any change in the groundwater system following the change in natural or artificial components. This study successfully applies MED to estimate the sequential recharge rates. As recharge rates are obtained by relative values, a series of timed observations are necessary. The validity of the estimated sequences of relative recharge rates can be checked by cross-referencing. Cross-correlations between the applied recharge sequence and the estimated results are above 0.985 in all study cases. Through the numerical test, the suitability of MED in the estimation of the recharge sequence to groundwater is investigated.

Stream nitrate variations explained by ground water head fluctuations in a pyrite-bearing aquifer.

In the context of agricultural nitrogen excesses in northwestern France, pyrite-bearing weathered schist aquifers represent important hydrological compartments due to their capacity to eliminate nitrate (NO3-). Under oxygen-free conditions, nitrate is reduced simultaneously with the oxidation of pyrite leading to the release of sulfate (SO4/2-). The aim of the present study is to identify the hydrological conditions under which the weathered schist ground water influences the stream water chemistry, leading to a decrease in NO3- concentration. We measured the ground water head on a small catchment over weathered schist, near the bank and under the streambed, and analyzed the chemical composition of the ground water as well as the stream water on both seasonal and storm-event timescales. Using SO4/2- as a tracer of the weathered schist ground water, we showed that ground water inflow caused a decrease of NO3- concentration in the stream during the autumn as well as during storm events in spring and summer. In summer, the NO3- concentration was controlled by the sources of the stream, and in winter by the shallow ground water inflow. The effect of the weathered schist ground water on the NO3- depletion remained relatively limited in time. This effect persisted into late autumn as long as the NO3(-) -rich shallow ground water did not feed the stream. The duration and intensity of the effect would be extended by decreasing the shallow ground water inflow, which depends on climate as well as the presence of landscape features such as hedges and buffer zones.

Analytical studies of groundwater-head fluctuation in a coastal confined aquifer overlain by a semi-permeable layer with storage

Analytical studies are carried out to investigate groundwater-head changes in a coastal aquifer system in response to tidal fluctuations. The system consists of an unconfined aquifer, a semi-confined aquifer and a semi-permeable confining unit between them. An exact analytical solution is derived to investigate the influences of both leakage and storage of the semi-permeable layer on the tide-induced groundwater-head fluctuation in the semi-confined aquifer. This solution is a generalization of the solution obtained by Jiao and Tang (Water Resource Research 35 (1999) 747–751) which ignored the storage of the semi-confining unit. The analytical solution indicates that both storage and leakage of the semi-permeable layer play an important role in the groundwater-head fluctuation in the confined aquifer. While leakage is generally more important than storage, the impact of storage on groundwater-head fluctuations changes with leakage. With the increase of leakage the fluctuation of groundwater-head in the confined aquifer will be controlled mainly by leakage. The study also demonstrates that the influence of storativity of the semi-permeable layer on groundwater-head fluctuation is negligible only when the storativity of the semi-permeable layer is comparable to or smaller than that of the confined aquifer. However, for aquifer systems with semi-permeable layer composed of thick, soft sedimentary materials, the storativity of the semi-permeable layer is usually much greater than that of the aquifer and its influence should be considered.

Comparison of univariate and transfer function models of groundwater fluctuations

Seasonal autoregressive integrated moving average (SARIMA) univariate models and single input‐single output transfer function (SARIMA with externalities or SARIMAX) models of groundwater head fluctuations are developed for 21 Upper Floridan aquifer observation wells in northeast Florida. These models incorporate empirical relationships between rainfall input and head response based on historical correlations and cross correlations between these two time series. The magnitude of the forecast error terms indicates that the SARIMA and SARIMAX models explain an average of 84–87% of the variation observed in the monthly piezometric head levels for 1‐month lead forecasts. Thus the models account for the dominant processes which affect temporal groundwater fluctuations. Both the SARIMA and SARIMAX models provide unbiased forecasts of piezometric head levels; however, the SARIMAX models produce more accurate forecasts (i.e., smaller forecast probability limits) than the SARIMA models, particularly as lead time increases. Modeling efforts reveal consistent model structures over the study region, with local hydrologic and geologic conditions causing site‐specific variability in the time series model parameters.

Soilwater dynamics related to waterlogging in a sloping catchment

A study to understand the factors contributing to waterlogging was conducted in a small catchment of 5.4 ha in an irrigation scheme in the Eastern Dry Zone of Sri Lanka. An analysis, based on climatological data, extensive measurements of inflows and outflows, groundwater head fluctuations, soil moisture content variations and soil properties, indicated that a single catchment water balance and the SEW index are of limited value due to the spatial nature of the waterlogging problem in this sloping catchment with surface irregularities. A distributed mathematical model was developed to represent the lateral and vertical components of flow; the agreement between the simulated and field results is satisfactory.