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Raw and adjusted groundwater levels at 16 gauging stations, with corresponding tidal levels measurements: a water levels in S1–S5 and tidal level in T1, b water levels in K1–K5 and tidal level in T2, and c water levels in L1–L6 and tidal level in T3 (reference water level was set as the annual mean sea level in Tokyo Bay). Solid lines represent the raw data. Dotted lines represent the adjusted water levels
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Observations of water levels in coastal aquifers and corresponding tides coupled with meteorological variances near the Ariake Sea show that groundwater in this area mainly fluctuates with atmospheric and tidal variations. Tidal effects occur with semi-monthly, diurnal, or semi-diurnal periodicity, whereas the barometric influences commonly act in...
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A wavelet multiresolution analysis is performed on atmospheric fields simulated by a multilevel 3-dimensional atmospheric boundary layer model. Wavelet cospectra of the vertical wind and potential temperature are calculated and compared with radial Fourier cospectra. The former indicate most of the field variance to have horizontal scales roughly e...
Citations
... Observed time series in boreholes, whether the groundwater head or EC, indicate the composition of various aquifer stresses. Each aquifer stress corresponds to a particular frequency or group of frequencies, with amplitude, period, and phase corresponding to each frequency (Dong et al., 2015). Every periodic and aperiodic function in time is decomposed by the Fourier transform into the sum of the sine and cosine functions (Proakis and Manolakis, 2006). ...
... Highest amplitude values are present for the periods of January, mid and late February, early April and May, mid and late October, and several changes during November and December (Fig. 5c). Those periods emphasize the nature of the cause of atmospheric pressure which is explained as a consequence of the air front movement along the pathway over different geographic locations (Dong et al., 2015;Merritt, 2004). The latter is different and should be distinguished from the daily changes in atmospheric pressure, mostly caused by day-night regime of the T change. ...
... The arrow representation has been shown to be a suitable method for visualising time lags between frequencies in two signals (Briciu, 2019;Zhang et al., 2020). Also, frequencies with periods between 2 and 4 h were removed from the spectrogram and coherence results because they correspond to noise frequencies (Dong et al., 2015) and to improve the visibility of frequencies of interest. Mean annual coherence values of 0.95 and 0.99 have been determined between diurnal and semidiurnal frequencies corresponding to SWL and GWL in P1, with an annual mean time lag of 2.68 h and 0.77 h standard deviation for the diurnal, and a time lag of 1.58 h and 0.24 h standard deviation for the semidiurnal component. ...
Study region:
River Neretva coastal aquifer system located in the south eastern part of Croatia.
Study focus:
The study is focused to determination of the seasonal and non-seasonal variations of the groundwater features, when influenced by external loadings found at the study area. Based on time series observed from the monitoring systems, in-situ profiling and observed external loadings, a spectrogram and coherence analysis is performed to detect the peculiarities of the groundwater regimes at three different subareas along the study area.
New hydrological insights for the region:
By using several methodological approaches, this paper emphasizes the combined effects of precipitation, river Neretva hydrological regime, melioration system operational regimes and tidal effects to the groundwater regime during the dry and rain seasons. During the dry period groundwater regime is mainly influenced by the seawater intrusion directly from the sea and from the river Neretva bed. Rain periods are characterized by the increase of the Neretva discharge thus eliminating the seawater from the river bed. This scenario results in improved quality of the groundwater. While Diga subarea faces active seawater intrusion, Jasenska's unconfined aquifer is fed by seawater from the river Neretva during the dry season. Vidrice is the only area where groundwater quality decreases during rain season due to the presence of salinized springs and the fact the area is found below the mean sea level.
... Shirahata et al. (2019aShirahata et al. ( , 2019b used tidal response methods to estimate the hydraulic parameters of aquifers beneath an island where appropriate groundwater development for agricultural use was desired. Accurate aquifer parameters are needed to construct and develop sinusoidal tidal components (Lanyon et al. 1982, Koizumi 1991, Ishitobi et al. 1993, Evans 2004, Möller et al. 2007, Alcolea et al. 2009, Aichi et al. 2011, Rahi & Halihan 2013, Acworth et al. 2015, Dong et al. 2015, Burgess et al. 2017, Fuentes-Arreazola et al. 2018, Shirahata et al. 2018. For this last purpose, Fourier analysis has the advantage of being simply performed using standard spreadsheet software with built-in functions (Whitford et al. 2001, Shirahata et al. 2018. ...
Fourier analysis applied to tidally fluctuating groundwater observation time series data can extract sinusoidal tidal components and help in the precise use of a tidal response method to estimate aquifer hydraulic parameters. To accurately isolate one tidal component with a specific period or accurately determine the amplitude and initial phase of the sinusoidal tidal component, an appropriate length for the time series to be analyzed must be selected. Errors are inevitable when Fourier analysis is used to isolate a tidal component from observation data due to the finite length of the analyzed time series. The errors stemming from two sources in the tidal-component isolation were extensively investigated using Fourier analyses of artificial time series with varying lengths that contained a major or relatively major tidal component. Based on the investigation, the recommended criteria for selecting time series lengths for the accurate isolation of major semidiurnal and diurnal tidal components were organized. The criteria, presented with their derivations, provide a practical guide for applying Fourier analysis to observation time series data to accurately isolate major tidal components.
... Most previous studies employed spectral analysis to identify the aquifer responses to possible influent factors, such as precipitation variability [9], tidal effects [10,11] and lake level fluctuations [12]. A spectral analysis can be used to evaluate the coherence and phase lag between external hydrological processes and groundwater-level responses in the frequency domains, and to estimate the degree of influence and travel time of external stresses to aquifers. ...
... A wavelet analysis assesses the variation in a signal in both the temporal and frequency domains [13]. In the field of hydrology, this technique is applied in two aspects: to determine the spatial and temporal variation of hydrological factors, including precipitation, river discharge and aquifer water levels [16][17][18][19]; and to quantify the interaction between hydrological variations and climatic indices, such as solar activity [11,20], the North Atlantic Oscillation [6,21], and the ENSO [20,22]. ...
Precise evaluation of the correlations among precipitation, groundwater and river water enhance our understanding on regional hydrological circulation and water resource management. The innovative and efficient use of wavelet analysis has been able to identify significant interactions in the spatial and temporal domains and to estimate the recharge travel time. In this paper, a wavelet analysis was utilized to analyse 43 years of monthly, and 2 years of daily, precipitation, river level and groundwater level data in the Yoshino River Basin, Japan. There were two main results: (1) There was a significant influence of precipitation and river on groundwater, with a periodicity of 4–128 days, 1 year and 2–7 years. The periodicity of 1 year was correlated with seasonal variability. The significant interaction at 4–128 days mainly occurred in the rainy season. The 2–7-year oscillation of aquifer water levels was determined by precipitation. (2) The recharge-water travel times in the study area estimated from the arrow patterns in the precipitation–groundwater wavelet coherence (WTC) were consistent for each observation well. The response times of the aquifer to precipitation were 1 day and 3–6 days in 2013 and 2014, respectively. The different time lags were likely determined by the timing of maximum daily precipitation.
... According to Purnama (2010), tides are one of the factors that affected groundwater level fluctuations, while (Levanon et al., 2016), showed there were interactions between these two attributes in the form of groundwater level position change. Dong et al. (2015) stated a seasonal and diurnal water level fluctuation in coastal aquifers is typically caused by oceanic tidal and barometric variations. On low coral islands, the groundwater lens is a vital source of freshwater for the terrestrial ecosystem and domestic consumption (White et al., 2007). ...
... -analytical solutions (Nielsen, 1990;Jeng et al., 2002;Dong et al., 2015;Huang et al., 2015 etc); -numerical modeling (Ataie-Ashtiani et al., 2001;Pauw et al., 2014;Levanon et al., 2016 etc); ...
... Field monitoring Investigate the influence of earth-tide in area study and identify processes contributing to salinity in tributary of the river Some researchers identified interactions of tides and groundwater with several methods. The analytical solutions was carried out by Nielsen (1990); Jeng et al. (2002); Dong et al. (2015); and Huang et al. (2015). The numerical modeling was carried out by Ataie-Ashtiani et al. (2001); Pauw et al. (2014); dan Levanon et al. (2016). ...
This research aims to identify the effect of tides on groundwater level fluctuation in Gili Ketapang Island by using a combination of field monitoring and hydrodynamic modeling. Groundwater data were collected from 5 July to 17 August 2018 from two wells monitoring, while the hydrodynamic model was adopted to identify sea-level conditions. The result explains the sea level around the island is similar among extremely strong correlations between the points. The hydrodynamic model proves a standing wave due to tidal amplification in Madura Strait waters. The effect of tides on the groundwater level characterized by decreasing in amplitudes and time lags as increasing the distance from the coast.
... Filtered signals are absent of all external stresses except tidal stresses and signal noise which is considered negligible. Detrendend signals are used for the identification and quantification of tidal influence on coastal aquifers [55,56]. Filtered signals were reconstructed from frequency domain back to time domain with Inverse Fast Fourier Transform (IFFT) also incorporated in Python SciPy library, thus enabling further analysis of detrended signals in time domain. ...
Sea water intrusion (SWI) has been widely recognized as a global problem, significantly influencing coastal aquifers, mostly through reduced water quality and agricultural production indicators. In this paper, we present the outcomes of the implementation of two independent real-time monitoring systems, planned and installed to get insights on groundwater dynamics within the adjacent coastal aquifer systems, one located in the Neretva Valley, southeastern Croatia, the other located south of the Venice lagoon, northeastern Italy. Both systems are presented with technical details and the capacity to observe, store, and transmit (Neretva site) observed values in real-time. Analysis of time series reveals the significant influence of the sea level oscillations onto the observed groundwater electrical conductivity (EC) and piezometric head values, while precipitation rate is detected as a driving mechanism for groundwater parameters in shallow geological units. The installed monitoring systems are shown to be of great importance to provide qualitative and quantitative information on the processes influencing groundwater and surface water dynamics within two coastal systems.
... The fluctuation in pore pressure successively propagates inland, and the propagation yields exponential decrement of amplitudes and linearly phased lags . The oceanic tide induces oscillation of the groundwater level (Carr and Van Der Kamp 1969;Dong et al. 2015) and the fresh-saline interface (Levanon et al. 2017). The depth to the fresh-saline interface from sea level is dependent on the aquifer permeability, thus the depth increases when permeability decreases (Schneider and Kruse 2003). ...
... For example, Kim et al. (2005) revealed that in coastal aquifers the groundwater level and the electrical conductivity are affected by changes in tidal level and rainfall, and the amount of transported water is larger in a coarser sand layer than in a finer sand layer. Dong et al. (2015) explained that the relation between groundwater level and sea level allows one to decipher the decrement of amplitude and the time lag in coastal aquifers. These studies suggest that fresh groundwater in highpermeability aquifers will be reduced by sea level rise and anthropogenic pumping. ...
In order to evaluate the behavior of a freshwater lens in the uplifted atoll island of Minami-Daito, Japan, groundwater level and electrical conductivity were simultaneously measured in six monitoring wells. The monitoring allowed determination of the position and variability of the top and bottom positions of the freshwater lens. The freshwater lens periodically oscillates with phase lags (delay time) every 3 h following sea tides. Recharge from local rainfall temporarily increases the volume of the freshwater lens but is disturbed by the low-permeability muddy sediments deposited on the central lowland of the island. Changes in the groundwater levels correlate well with rainfall, after first removing semi-diurnal, diurnal, and long-term components of the sea tides from the groundwater level data using a multiple regression analysis. Changes in the water electrical conductivity provide information on the temporal and spatial fluctuation of the freshwater lens. The monitoring scheme for this freshwater lens could be applied to other uplifted atolls, contributing to better evaluation of the potable groundwater resources and to making freshwater use sustainable on other islands.
... Tide-induced fluctuations also influence the salinity of groundwater because the transition zone between saltwater and freshwater has been observed to move back and forth with tidal variation (Ataie-Ashtiani et al. 2001;Robinson et al. 2006;Kang and Lin 2007). Additionally, as the inshore distance increases, the tidal effect gradually decreases, and the groundwater level is more influenced by barometric variations (Dong et al. 2015). Holman et al. (2011) extended the relationship with groundwater level to climatic indices such as the North Atlantic Oscillation and East Atlantic pattern. ...
The influence of lunar semidiurnal tides on coastal groundwater aquifers has been conceptualized for decades. However, a thorough understanding of the impact of tides on groundwater dynamics due to the widely distributed waterways and heterogeneous sediments in estuarine aquifers, is still needed. This study shows the tidal impact on groundwater dynamics in the Pearl River estuary in southeast China through wavelet and time series analysis. The groundwater level and electrical conductivity (EC), as well as tidal levels, were monitored in several observation wells and tidal stations to determine how the estuarine groundwater levels respond to tidal forcing. The results show that the groundwater fluctuations have short periodicities of 0.51 and 1 day corresponding to major tidal constituents of M2 (semidiurnal) and K1 and O1 (diurnal) signals, respectively. The significant impacts decrease with increasing distance inland of the locations of the wells. Additionally, the coherence analysis displays a higher correlation between tides and groundwater levels for the spring tide than for the neap tide. The tidal influences on groundwater EC are weak compared to those on groundwater levels. In addition, when the tidal level increases, the EC decreases in wells located in the estuarine entrance. This is related to the high salinity of retained paleo-seawater in the strata lenses. A conceptual model is proposed to illustrate the complex groundwater flow dynamics. The model may provide useful insights into the understanding of similar systems located in geographically different coastal regions.
... Because some of the tidal methods imply the knowledge of loading efficiency [9,14,26], barometric efficiency, , has to be determined to characterize tidally induced changes inland from the shoreline. The topic of excluding the effects of barometric pressure from observed groundwater level was of interest in several publications [41][42][43][44][45][46][47][48][49][50][51], whereas determination can be approached by time domain or frequency domain analysis [50]. ...
... If the external stress represented by barometric pressure is transmitted to the aquifer, reaction stress can be divided between the sediments that the aquifer is made of and water contained within the aquifer pore volume. Because represents the percentage of stress that is accommodated by the sediment matrix [43,44,50], a zero value corresponds to no response case, whereas a unity value respresents a fully efficient response to barometric changes. In case of a zero value, total barometric pressure-induced stress is accommodated by the pore water, whereas for a unity BE value, total stress is accommodated purely by sediment matrix. ...
Hydrogeological data availability is often limited to local areas where usual in situ tests or methods are applied (slug/bail or pumping tests, Electrical Resistivity Tomography (ERT)). Because most problems (e.g., saltwater intrusion mitigation) require problem analysis on larger scales (catchment or sub catchment), hydrogeological identification of global character is preferable. This work leads to the determination of aquifer hydrogeological parameters on the basis of observed sea level, groundwater piezometric head found inland, and barometric pressure. When applied to observed signals, the approach led efficiently to final hydrogeological characterization. After identification of dominant tidal constituents from observed signals, barometric efficiency was successfully determined. Following available information on geological settings, an appropriate conceptual model was applied and updated to count for polychromatic signals. Final determination of hydrogeological parameters relied on root mean square error (RMSE) minimization and led to determination of (i) presence of three stratigraphic units: unconfined sandy aquifer on the top, a confining layer made of clay, and a confined gravel layer; (ii) existence of the clay layer under the sea with a total length of 1400 m; (iii) a clay layer has been identified as confining one by both spectral analysis and determined leakance value; and (iv) estimated confined aquifer specific storage ranging from 2.87 × 10 −6 to 4.98 × 10 −6 (m −1), whereas hydraulic conductivity ranged from 7.0 × 10 −4 to 7.5 × 10 −3 (m s −1). Both range intervals corresponded to previous in situ findings conducted within the area of interest.
... (e.g.Dong et al. 2015; Acworth et al. 2016), but the most commonly used are sinusoidal functions. The decomposition of a time series into sinusoidal functions is commonly undertaken using Fourier Transform methods (Kanasewich 1981), such as the Discrete ...
Groundwater responses to barometric pressure fluctuations are characterised using the concept of barometric efficiency. For semi‐confined and confined aquifers, barometric efficiency (BE) values can be used to provide efficient, low‐cost estimates of specific storage. This study compares, for the first time, eight existing methods of barometric efficiency estimation. Comparisons were undertaken using data from the Peel region of Western Australia. Fourier analysis and regression deconvolution methods were used to estimate aquifer confinement status. The former approach was found to be robust and provided a quantitative basis for spatial comparisons of the degree of confinement. The latter approach was confounded by the presence of diurnal and/or semi‐diurnal signals. For wells at which semi‐confined or confined responses were identified, frequency and time domain methods were used to estimate BE values. Most barometric efficiency estimation methods were similarly confounded by diurnal and/or semi‐diurnal signals, with the exception of the Acworth et al. (2016) method. Specific storage values calculated from BE values were order‐of‐magnitude consistent with the results of four historical pumping tests. The methods implemented in this research provide efficient, low‐cost alternatives to hydraulic testing for estimating aquifer confinement, as well as the barometric efficiency and specific storage of semi‐confined and confined aquifers. The frequency and duration of observations required by these methods are minimal; for example, typically requiring a minimum of four observations per day over a four month period. In some locations they may allow additional insights to be derived from existing groundwater hydrograph data. This article is protected by copyright. All rights reserved.
... On the contrary, when the water table falls, extra pore space and negative pressures are generated (Jiao and Li, 2004). Dong et al. (2014) studied a coastal aquifer near the Ariake Sea, where the groundwater level of the coastal aquifer fluctuated with tidal and barometric variations. Here, spectral analyses also revealed that the sea-tidal effects could influence the semi-monthly, diurnal, and semidiurnal periodicities, associated with the astronomical tidal variations. ...
Due to their large carbon storage capacity and ability to exchange subterranean CO2 with the atmosphere, soils are key components in the carbon balance in semi‐arid ecosystems. Most studies have focused on shallow (e.g., <30 cm depth) soil CO2 dynamics neglecting processes in deeper soil layers where highly CO2‐enriched air can be stored or transported through soil pores and fissures. Here, we examine the relationship among variations in subterranean CO2 molar fraction, volumetric water content, soil temperature and atmospheric pressure during three years within soil profiles (0.15, 0.50, and 1.50 m depths) in two semi‐arid grasslands located in southeastern Spain. We applied a wavelet coherence analysis to study the temporal variability and temporal correlation between the CO2 molar fraction and its covariates (soil temperature, soil moisture and atmospheric pressure). Our results show that CO2 dynamics are strongly influenced by changes in atmospheric pressure from semidiurnal, diurnal and synoptic to monthly time‐scales for all soil depths. In contrast, only weak daily dependencies were found at the surface level (0.15 m) regarding soil temperature and volumetric water content. Atmospheric pressure changes substantially influence variations in the CO2 content (with daily fluctuations of up to 2000 ppm) denoting transportation through soil layers. These results provide insights into the importance of subterranean storage and non‐diffusive gas transport that could influence soil CO2 efflux rates, processes that are not considered when applying the flux‐gradient approach and, which can be especially important in ecosystems with high air permeability between the unsaturated porous media and the atmosphere.
