River Aquifer Systems Research Articles

Loading effect of phreatic level variations induced by river tide on groundwater head fluctuations in tidal river aquifer systems

The unconfined groundwater level variations caused by the river tide can impact the fluctuation of the groundwater head in the underlying confined aquifer by loading effect. In this study, we proposed a mathematical model and provided an analytical solution for a confined aquifer system considering the loading effect when the aquifer system is eroded by the tidal river to varying extents. The results demonstrated that the loading effect tends to amplify the amplitude of the tide-induced head fluctuation while reduce its phase shift in the confined aquifer. These effects are more significant with a larger tidal loading efficiency, a wider tidal river, and a smaller tidal propagation parameter of the unconfined aquifer. The analytical solution was validated by the observed groundwater level fluctuations from a groundwater level monitoring well near a tidal river in the Peral River Delta of China, and provided reliable estimations of aquifer parameters in the region.

Exact simulation of the groundwater flow in anisotropic confined aquifer near time-varying streams by comprehensive new analytical solutions

This paper presents some new analytical solutions to an accurate prediction of the behavior of the groundwater flow in aquifers in response to changes in surface water. The new analytical solutions are obtained using integral transforms. An anisotropic rectangular confined aquifer bounded with four time-varying streams is undertaken. The effects of anisotropy on groundwater head and flow rate near time-varying streams are investigated. Depending on the change rates of the streams level, an anisotropic aquifer may render either lower or higher hydraulic head than an isotropic aquifer. In addition, an anisotropic aquifer has provided less water exchange at the interfaces than an isotropic one. The sensitivity of the hydraulic head to change rate of the streams level in both isotropic and anisotropic aquifers is evaluated. It is shown that the aquifer response is more sensitive to change rate of the streams parallel to y-direction and less sensitive to change rate of the streams parallel to x-direction in an anisotropic aquifer and vice versa in an isotropic aquifer. The results of the present new analytical solutions are compared with numerical model of MODFLOW. The results obtained from the presented solutions showed good agreement with the results of MODFLOW. The results show that the presented new analytical solutions are accurate, robust and efficient. Therefore, the results indicate that the presented new analytical solutions are very effective in the simulation of the groundwater flow in river–aquifer systems. Furthermore, one of the advantages of the new analytical solutions is to investigate the sensitivity analysis of aquifer parameters, which has been carried out in this paper. Also, some other new analytical solutions for steady-state conditions and sudden fall in streams level are provided as well. Feasibility of the proposed new analytical solutions is presented via calculating and simulating the hydraulics of groundwater flow in river–aquifer systems by means of integral transforms.

Modeling the river-aquifer via a new exact model under a more general function of river water level variation

The interaction between surface water and groundwater is a significant topic in groundwater-related problems. This study suggests an exact model based on Laplace transformation to calculate the groundwater flow in river-aquifer systems. Exact models play an important role in simulating the future behavior of river-aquifer systems. Therefore, investigation of the exact models for river-aquifer systems is a hot topic in the hydraulics of groundwater flow modeling. The objective of this research is to present new exact models for simulating the hydraulics of groundwater flow in river-aquifer systems with a more general function of river level variation under recharge by means of Laplace transform method. A general function is adopted to describe the river level variation, in which some situations such as linear, exponential and power of time variations in the river level can be treated as special cases. The effects of variations in aquifer parameters on groundwater hydraulic head are evaluated. It is shown that the groundwater hydraulic head grows slower in aquifers with a greater thickness or hydraulic conductivity. In addition, the effect of changes in specific storage is too little on the groundwater hydraulic head. The variations in hydraulic heads due to changes in recharge rate with different values of thickness, hydraulic conductivity, specific storage, and length are analyzed. It is observed that the groundwater hydraulic head in an aquifer with a lesser length, higher hydraulic conductivity or higher thickness is less sensitive to a change in the recharge rate than in an aquifer with a higher length, lesser hydraulic conductivity or lesser thickness. Furthermore, it is shown that the differences in hydraulic heads due to the increase in recharge rate are not significant for different values of specific storage. The results of the present new exact models are successfully verified by the results obtained from the analytical solution of Bansal and Das. Also, for more reliability, the results are compared with those results of MODFLOW. The results show that the presented new exact models are accurate, robust and efficient. One of the advantages of the solutions is to investigate the sensitivity analysis of aquifer parameters, which has been carried out in this paper. Furthermore, in the present research a more general function describing river level variation is considered, in which the linear, exponential and power of time variations are special cases.

Research Trends in Groundwater and Stable Isotopes

Groundwater is essential in the management of water resources globally. The water quality of aquifers is affected by climate change and population growth, aspects that can be addressed with stable isotope analysis. This study aims to carry out an analysis of the scientific information related to groundwater and stable isotopes (GSI) using scientific databases (Scopus and Web of Science) to evaluate the intellectual structure of the subject and the emerging research lines. The methodology includes: (i) topic search selection, (ii) tools in databases processing, (iii) bibliometric analysis, and (iv) review by clustering technique. The results showed that the scientific production of GSI can be addressed through three evolution periods: I (1969–1990), II (1991–2005), and III (2006–2021). Periods I and II did not significantly contribute to publications because, in the past, most of the student’s thesis (M.Sc. and Ph.D) consisted of writing a report that summarizes their works. Therefore, the researcher was not obliged to publish their results in a professional journal. Finally, the third period showed exponential growth, representing 82.34% of the total publications in this theme because, in the last years, institutions require at least one scientific article depending on the country and university, in order to graduate with an M.Sc. and PhD. Finally, the contribution of this study is reflected in the recognition of new research lines and their applicability by the knowledge of recharge sources, environmental aspects, infiltration, knowledge of the aquifer-meteoric water system, and groundwater-superficial water interaction. These aspects offer the possibility of analyzing integrated water resources management at the watershed or river-aquifer systems level.

Analysis of a steady-state model of groundwater discharge in a river valley without and with evapotranspiration

Riparian evapotranspiration is an important process that constrains water exchanges within a well-connected river–aquifer–vegetation hydrological system. In this study, we developed an extended analytical Dupuit–Forchheimer (DF) model to consider the additional water flow resistances due to both the vertical deformation of flow lines caused by evapotranspiration and discharge into the river screened by bottom sediments in which a river does not fully penetrate the aquifer. This analytical model can describe the groundwater discharge process in the presence of riparian evapotranspiration. We validated our analytical results with numerical simulations of a 2-D flow model that explicitly considers vertical hydraulic resistances, demonstrating that the surface water–groundwater exchanges in such hydrological systems are strongly dependent on the hydrogeological parameters, river width, riparian zone width, and parameters related to the hydraulic connection between evapotranspiration and groundwater. A sensitivity analysis of our extended DF model reveals that the water balance in hyperarid regions is determined by riparian evapotranspiration, and evapotranspiration most likely causes river flow losses. However, in humid regions, most groundwater (80% or more) is discharged into rivers rather than via riparian evapotranspiration. Our results confirm that riparian evapotranspiration in arid regions is an important process that affects surface water–groundwater exchanges and that evapotranspiration from riparian zones not only reduces groundwater discharge into rivers but also potentially causes disconnections within river–aquifer systems. The obtained analytical dependencies allow the grid-dependent parameters of the RIV and EVT packages to be calculated in the MODFLOW simulations of regional groundwater flow discharge in a river valley using coarse grids.

A distributed domain model coupling open channel flow and groundwater flow to quantify the impact of lateral hydrologic exchange on hydrograph

• A distributed-domain coupling model is developed to evaluate the interaction between hydrologic exchange flows and river hydrodynamics. • The buffering effect of lateral HEFs can dominate flood wave patterns. • The falling limb (with a power-law rate) of hydrographs is linked to spatially heterogeneous hydraulic properties. Hydrologic exchange flows (HEFs) of river-aquifer systems are known to affect water flow, but the quantitative influences of lateral HEFs and the riparian zone’s hydraulic conductivity ( K ) distribution on stream fluxes remain obscure under varying hydrologic conditions. To fill this knowledge gap, this study proposed a physical based, distributed domain, coupled (open channel and groundwater) flow model (DDCM) to quantify the effect of lateral HEFs on hydrograph characteristics, including especially the peak discharge and tailing decay which are practically important. Numerical experiments showed that (1) the interaction between the lateral HEFs and river hydrodynamics reduced the peak discharge and flood flow rates, (2) a heterogeneous K field of the riparian zone generated multi-rate HEFs (which then changed flow response) represented by the hydrographs with various declining rates (varying from exponential to power-law), significantly expanding the flow process, and (3) the probability density function of K also affected the tailing and peak of the hydrograph. A preliminary test showed that the DDCM captured the overall pattern of hydrographs observed from a catchment in the Wadi Ahin West, Oman. This study, therefore, provided a model-based quantification of the mechanisms and factors of the lateral HEFs affecting the hydrograph pattern in flood events, and further applications are needed to test the applicability of the DDCM in capturing real-world hydrographs affected by the lateral HEFs.

Modeling Semiarid River–Aquifer Systems with Bayesian Networks and Artificial Neural Networks

In semiarid areas, precipitations usually appear in the form of big and brief floods, which affect the aquifer through water infiltration, causing groundwater temperature changes. These changes may have an impact on the physical, chemical and biological processes of the aquifer and, thus, modeling the groundwater temperature variations associated with stormy precipitation episodes is essential, especially since this kind of precipitation is becoming increasingly frequent in semiarid regions. In this paper, we compare the predictive performance of two popular tools in statistics and machine learning, namely Bayesian networks (BNs) and artificial neural networks (ANNs), in modeling groundwater temperature variation associated with precipitation events. More specifically, we trained a total of 2145 ANNs with different node configurations, from one to five layers. On the other hand, we trained three different BNs using different structure learning algorithms. We conclude that, while both tools are equivalent in terms of accuracy for predicting groundwater temperature drops, the computational cost associated with the estimation of Bayesian networks is significantly lower, and the resulting BN models are more versatile and allow a more detailed analysis.

Three dimensional model for solute transport induced by groundwater abstraction in river-aquifer systems

This study consider the development of three dimensional analytical solutions for contaminant transport induced by a pumping well near a stream. The solutions were derived for both line-width and finite-width streams based on Green’s function approach. These solutions were implemented in an aquifer that was partially penetrated by the stream and were general enough to be applied to both unconfined and confined aquifers. The analytical solutions were checked to show the effect of stream width, leakance coefficient, distance from the river edge to pumping well and pumping rate on contaminant concentration. Generally, it was found that higher values of these parameters increased the contamination in the well area for both line and finite width stream. The graphical representation of the analytical solution shows that the contaminants attenuated vertically along z axis as well as horizontally along × axis. The finite width model produced more realistic estimate for the distribution of contaminants due to the effect of river width. In particular, the results shows higher contamination near the stream for finite width model. However, this impact of river width on contaminant concentration appear to be neglected if the distance between river and pumping well was more than twice the stream width.

Evaluation of nitrate sources and the percent contribution of bacterial denitrification in hyporheic zone using isotope fractionation technique and multi-linear regression analysis

Denitrification has documented as a promising pathway to permanently remove nitrate from a system. Numerous studies have used the isotope fractionation technique (IFT) to evaluate the denitrification rate in the constructed wetlands (CWs), but the potential of IFT method to quantify the denitrification rate in hyporheic zone (saturated sediments beneath a stream) is still challenging. Thus, more studies are required to investigate that if measurements of the natural abundance of δ15N-NO3- and δ18O-NO3- (IFT) can be employed to calculate the fate of nitrate in hyporheic zone. Therefore, in this study, the possibility of the IFT to quantify the hyporheic-denitrification rate was investigated. Then, the results were verified by the combined application of the pre-established net Sediment N2 flux and multi-linear regression analysis (p < 0.01). Finally, the groundwater bacterial groups (Fecal coliform (FC) and Escherichia coli (EC)), and the mass balance isotope mixing model were used to investigate the dominant sources of hyporheic-nitrate. The IFT reveals that denitrification contributes 74.1% and 29.1% of the hyporheic-nitrate removal during dry and wet seasons, respectively. The multi-linear regression analysis, considering at 99% confidence interval (R2 = 92.1%; n = 44; p < 0.01), slightly overestimates the rate and the percent contribution of denitrification in the dry season (475.15 ± 101.18 μmol/m2d; 80.7%) and underestimates it during the wet season (205.072 ± 35.39 μmol/m2d; 24.01%). The analysis of EC and FC demonstrates that manure (41.9 ± 4.2%) and sewage (54.1 ± 8.9%) are the dominant contributors of the hyporheic-nitrate load. In addition, the results achieved by the analysis of the fecal bacterial indicators (EC and FC) were confirmed by NO3−/Cl− vs Cl− diagram. This study provides an alternative-initiative framework to accurately quantify the spatio-seasonal variations in the hyporheic-nitrate sources and hyporheic-denitrification rate that enables decision-makers to apply appropriate and targeted strategies to regulate nitrate load in river-aquifer systems.

The nitrogen cycle in highly urbanized tropical regions and the effect of river–aquifer interactions: The case of Jakarta and the Ciliwung River

Groundwater is extensively used in Jakarta to compensate for the limited public water supply network. Recent observations show a rise in nitrate (NO3−) levels in the shallow aquifer, thus pointing at a potential risk for public health. The detected levels are still below national and international regulatory limits for drinking water but a strategy is necessary to contain the growing problem. We combine 3years of available data in the Ciliwung River, the major river flowing through Jakarta, with a distributed river–aquifer interaction model to characterise the impact of urbanisation on the N-cycle of both surface and groundwater systems. Results show that the N-cycle in the river–aquifer system is heterogeneous in space, seasonal dependent (i.e. flow regime) and strongly affected by urban pollution. Results suggest also that although the main sources of N related groundwater pollution are leaking septic tanks, the aquifer interaction with the Ciliwung River may locally have a strong effect on the concentrations. In the general context of pollution control in urban areas, this study demonstrates how advanced process-based models can be efficiently used in combination with field measurements to bring new insights into complex contamination problems. These are essential for more effective and integrated management of water quality in river–aquifer systems.

A numerical modelling and neural network approach to estimate the impact of groundwater abstractions on river flows

Summary Evaluation of the impacts of groundwater abstractions on surface water systems is a necessary task in integrated water resources management. A range of hydrological, hydrogeological, and geomorphological factors influence the complex processes of interaction between groundwater and rivers. This paper presents an approach which uses numerical modeling of generic river–aquifer systems to represent the interaction processes, and neural networks to capture the impacts of the different controlling factors. The generic models describe hydrogeological settings representing most river–aquifer systems in England and Wales: high diffusivity (e.g. Chalk) and low diffusivity (e.g. Triassic Sandstone) aquifers with flow to rivers mediated by alluvial gravels; the same aquifers where they are in direct connection with the river; and shallow alluvial aquifers which are disconnected from regional aquifers. Numerical model simulations using the SHETRAN integrated catchment modeling system provided outputs including time-series and spatial variations in river flow depletion, and spatially distributed groundwater levels. Artificial neural network models were trained using input parameters describing the controlling factors and the outputs from the numerical model simulations, providing an efficient tool for representing the impacts of groundwater abstractions across a wide range of conditions. There are very few field data sets of accurately quantified river flow depletion as a result of groundwater abstraction under controlled conditions. One such data set from an experimental study carried out in 1967 on the Winterbourne stream in the Lambourne catchment over a Chalk aquifer was used successfully to test the modeling tool. This modeling approach provides a general methodology for rapid simulations of complex hydrogeological systems which preserves the physical consistency between multiple and diverse model outputs.

Steady Groundwater Flow with Steep Gradients: An Analytic Approach to the 2D–Problem with a Vertical Pressure Boundary Condition and Steady Recharge/Drainage

AbstractSteady groundwater flow with steep gradients in a vertical plane due to superficial recharge/drainage, inner sources/sinks and a one‐sided pressure boundary condition can be described by a 2D Poisson equation with a nonlinear free surface boundary condition. By means of conformal mapping techniques Schmitz and Edenhofer [1] derived the exact explicit solution of this problem in a horizontally infinite aquifer. Their results are extended to problems with a one‐sided vertical pressure boundary condition, modelling f. ex. the boundary between an aquifer and an adjacent free water body. According to ist simple parametrization, this approach can be applied on one hand to model various real world phenomena like river–aquifer–systems. It may on the other hand serve as a tool for investigating the exactness of numerical solutions and the range of validity of simplifying assumptions. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Distribution patterns of interstitial freshwater meiofauna over a range of spatial scales, with emphasis on alluvial river-aquifer systems

Spatial distribution patterns of the interstitial meiobenthos are examined across a range of scales. A global interstitial highway model is presented with the alluvial aquifer system as its central core. Spatially discontinuous hypogean entities, such as karstic aquifers, springs, anchialine waters and the psammolittoral, have limited interconnections except through the alluvial aquifer system and are contiguous with epigean waters. The global interstitial highway is viewed as an evolutionary pathway and long-term dispersal route for meiobenthic forms. The distribution of interstitial animals in alluvial river-aquifer systems is examined at longitudinal (altitudinal), reach, floodplain, gravel bar, and vertical (depth) scales. Geomorphic and hydrogeologic features and interactions emerge as major determinants of the spatially heterogeneous nature of alluvial aquifers that structure the patchy distribution patterns of hypogean fauna across a range of scales.