Constant Head Boundary Research Articles

Inverse method to determine hydraulic conductivity from a velocity field using graph theory

A numerical inverse method called FlowPaths is presented to solve for the hydraulic conductivity field of an isotropic heterogeneous porous medium from a known specific discharge field (and constant-head boundary conditions). This method makes possible a new approach to reactive transport experiments, aimed at understanding the dynamic spatial and temporal evolution of hydraulic conductivity, which simultaneously record the evolving reaction and the evolving flow geometry. This inverse method assumes steady, two-dimensional flow through a square matrix of grid blocks. A graph-theoretical approach is used to find a set of flow paths through the porous medium using the known components of the specific discharge, where every vertex is traversed by at least one path from the upstream high-head boundary to the downstream low-head boundary. Darcy’s law is used to create an equation for the unknown head drop across each edge. Summation of these edge equations along each path through the network generates a set of linearly independent head-drop equations that is solved directly for the hydraulic conductivity field. FlowPaths is verified by generating 12,740 hydraulic conductivity fields of varying size and heterogeneity, calculating the corresponding specific discharge field for each, and then using that specific discharge field to estimate the underlying hydraulic conductivity field. When estimates from FlowPaths are compared to the simulated hydraulic conductivity fields, the inverse method is demonstrated to be accurate and numerically stable. Accordingly, within certain limitations, FlowPaths can be used in field or laboratory applications to find hydraulic conductivity from a known velocity field.

Analytical solutions for freshwater lenses in stratified riparian aquifers

Analytical solutions for defining stable freshwater lenses within saline riparian aquifers (“riparian lenses”) are largely limited to homogenous aquifers. However, real-world riparian aquifers typically consist of a surficial layer of low-permeability soils or deposits, the impact of which on the occurrence of riparian lenses has not been investigated. This study develops steady-state, sharp-interface analytical solutions for riparian lens shape and saltwater discharge in a two-layered riparian aquifer. The developed analytical solutions are verified by sand tank experiments and numerical simulations, showing good agreement. The sensitivity analysis based on the proposed analytical solutions suggests that aquifer stratification (i.e., considering a low-permeability layer overlying a high-permeability layer) leads to larger lenses in head-controlled systems (i.e., with the inland constant-head boundary) but smaller lenses in flux-controlled systems (i.e., with the inland constant-flux boundary), compared to the scenario of a homogenous aquifer. The surficial layer with hydraulic conductivity only an order of magnitude lower than the underlying high-permeability layer would have a pronounced effect on lens extent and volume. Importantly, the results suggest that the presence of the surficial low-permeability layer may lead to the outcropping of the groundwater table, favoring the occurrence of saline groundwater seepage near the edge of the river valley (i.e., a phenomenon reported by the field survey of the Murray River floodplains in South Australia). The analytical solution presented in this study can be used to provide a preliminary assessment of riparian lenses in saline stratified aquifers, expanding the applicability of analytical methods to more realistic riparian settings.

Optimal strategies for assigning prior boundary settings in Hydraulic Tomography analysis

Hydraulic Tomography (HT) is a high-resolution method for identifying aquifer hydraulic property heterogeneity. Despite decades of development leading to a relative maturation of HT, the influence of prior boundary information on HT estimations warrants further investigation. In this study, HT methods were applied to a synthetic heterogeneous aquifer to examine the impact of prior boundary types, sizes, and head values on parameter estimations. Results indicate that while boundary size has limited impact on HT outcomes regardless of data adequacy, the boundary condition type is a significant factor in HT inversion. Increasing boundary size can mitigate errors from incorrect boundary type assumptions. The SimSLE-HCA iterative algorithm effectively estimates optimal boundary head values given sufficient HT survey data. For practical application, in cases where the boundary size is unknown, a moderate expansion of the simulation area is recommended. In situations where the boundary type is uncertain, designating it as a constant head boundary proves practical.

Coupled hydrogeological modeling and nitrate transport modeling in an anthropized valley, a case study of the lower Soummam valley (Bejaïa Northeast of Algeria)

Anthropogenic activities, including wastewater discharges and fertilizer use, were identified as the primary factors influencing nitrate concentrations in the lower Soummam Valley in the North-East of Algeria. This study aimed to investigate nitrogen pollution and simulate nitrate mass transport coupled with a numerical flow model. Hydrogeochemical findings revealed significant seasonal variations between the high-water period (May 2019 and 2021) and the low-water period (September 2019 to November 2020 and 2021). During the low-water period, both temperature and electrical conductivity increased. However, pH, dissolved oxygen, and nitrate levels decreased in the high-water period. Nitrites and ammonium exhibited irregular fluctuations. The numerical flow model was developed using PMWIN and coupled with a solute transport model simulated with the Model Transport 3 Dimensions (MT3D). Calibration was conducted under steady-state conditions from 2011 to 2021 and was validated by comparing piezometric heads and nitrate concentrations measured in May 2021. Three scenarios were devised to simulate transient conditions from 2011 to 2050, considering variations in both groundwater levels and nitrate concentrations. The simulation revealed that river and dependent head boundaries are the primary sources of groundwater recharge. These boundaries contributed to approximately 87% of the total inflow. The model also depicted the water exchange between the aquifer and the river. However, the constant head boundary represented the main outflow, accounting for 85.7% of the total. The nitrate model illustrated an increase in nitrate concentrations, reaching 3.8 mg/L in 27 out of the 29 simulated wells. Both the river and groundwater head boundaries were identified as the key factors governing the hydrodynamic aquifer system and nitrate transport in the alluvial aquifer of the lower Soummam Valley.

Hydrogeological conceptual model in the Batang Integrated Industrial Park, Central Java, Indonesia

The construction of Batang Integrated Industrial Park (BIIP) will surely affect the groundwater in this area and its surroundings. To estimate the impact of changes in land use and the potential use of industrial water from groundwater, a hydrogeological conceptual model has been constructed for the BIIP. The methodology involves gathering rainfall data to estimate potential recharge. The secondary and primary data of deep and shallow wells were used to evaluate the boundaries of groundwater flow directions and develop the geometry of the aquifer system. The boundary condition observation data, geophysics data, drilling log, and slug test results were collected and interpreted in a 2-dimensional as a conceptual model of the hydrogeological condition. The result reveals that groundwater flow boundaries are Java Sea in the North as a constant head boundary, Brontak River in the west, Pesanggrahan River in the east as a river boundary, and Srigunung hills in the south as a no-flow boundary. The aquifer system of the area is dominated by sand as an unconfined aquifer with a thickness maximum of 88 m and located up to 47 m below the surface. The recharge in the research area is approximately 950.5 mm/year. The hydraulic conductivity of the aquifers is 0.16 m/day to 0.401 m/day. This hydrogeological conceptual model provides essential information for numerical groundwater models.

Fracture connectivity and flow path tortuosity elucidated from advective transport to a pumping well in complex 3D networks

Conservative, non-sorbing particle arrivals to a pumping well are used to provide high-resolution data to explore network connectivity and flow path tortuosity as a function of scale for a series of complex 3D discrete fracture networks (DFNs). The DFNs are stochastically generated using orientations ranging from random to three orthogonal planes, power-law distributions of length, and a broad range of density ranging from sparse to moderately dense networks. The internal architecture of the DFNs is intensively sampled by distributing conservative particles evenly over all fractures within a large spherical release volume. A non-directional framework featuring a radially convergent flow field, established by applying a weak sink in the center of the model domain and assigning equal-value constant head boundaries to all sides of the model domain, is used to minimize directional dependence on network connectivity. Results indicate particle velocity is significantly influenced by fracture set orientation in the degree to which fracture sets promote fracture connectivity, and that broad distributions of ensemble velocity can arise from networks with constant fracture transmissivity where slower velocities are characteristic of particle placement into fracture elements less connected to the sink, and vice versa. Inverse particle velocity is strongly power-law for all networks tested and indicates persistent and diverse retention characteristics. The degree of retention decreases in the transition from poorly- to well-connected networks and with increasing distance of particle release due to the availability of more fracture pathways with stronger connection to the sink. Tortuosity is exponentially distributed for all networks tested with median values that stabilize over a distance approximately 10 times the minimum fracture length, and is most sensitive to fracture length, followed by orientation and density.

The Saint‐Venant type isoperimetric inequalities for assessing saturated water storage in lacunary shallow perched aquifers

AbstractThe Dupuit‐Forchheimer (DF) approximation for unconfined groundwater flows is reduced to 2D Poisson's equation (PE), the right hand side of which involves an intensive evapotranspiration (ET) rate. A shallow water table dips inward from a constant piezometric head boundary (closed curve) such that a “dry gap,” demarcated by another closed curve (unknown front), may emerge. Apriori estimates of the volume of the saturated zone and of the “dry gap” area are important for water resources management in drylands. We use the results from the theory of linear elasticity, torsion of elastic bars, for which PE is solved for the Prandtl function. Using the Poincaré metrics with the Gaussian constant curvature , isoperimetric inequalities are obtained for steady‐state DF flows. Conformal moments and confromal radii of the domains and 2‐D Hardy's type inequalities in domains, modeling the Saint Venant bar torsion problem, are involved in the obtained estimates. The studied boundary value problems (BVPs) are nonlinear for ET rates depending on the depth of the water table. In the DF model, the vadose zone (VZ) is considered as a “distributed sink” (similar to a standard “distributed source,” which models recharge to the water table in humid climates). The analytical VZ is collated with one obtained from a numerical solution to BVP for Richards’ equation in a 3‐D saturated‐unsaturated flow. BVPs for Richards’ equation in cylindrical domains, solved by HYDRUS software, give the pressure head, moisture content, Darcian velocity fields, and streamlines.

Analytical solutions for seawater intrusion and the maximum pumping rate of a well in unconfined coastal aquifers bounded by L-shaped coastlines

Determining the maximum pumping rate (i.e., the maximum allowable pumping rate that does not cause seawater intrusion into the well under the steady-state condition) of a well is the key for sustainable management of coastal aquifers, as overexploitation of coastal aquifers could lead to the widespread occurrence of aquifer salinization (i.e., seawater intrusion). In this study, we develop steady-state analytical solutions to describe seawater intrusion and the maximum pumping rate of a well located in unconfined coastal aquifers bounded by L-shaped coastlines. Rectangular coastal aquifers bounded by two orthogonal constant-head boundaries (i.e., two coastlines) and two orthogonal no-flow inland boundaries are assumed in conceptual models, where replenishment of aquifers is via surface recharge. Analytical solutions are derived by the potential theory and the conformal mapping method, and validated by variable-density flow numerical simulations. It is found that analytical solutions based on the sharp-interface approximation overestimate seawater intrusion and underestimate the maximum pumping rate. An acceptable, conservative maximum pumping rate is obtained by using the correction factor proposed by Lu and Werner (2013). Moreover, the sensitivity of the well location on the maximum pumping rate is investigated, showing that an optimal well location exists. Analytical solutions developed in the current study provide a convenient tool for assessing pumping effects in coastal aquifers bounded by L-shaped coastlines, servicing to various management objectives.

Impact of Water Gushing Influenced by the Relationship between Fault and Tunnel Position

In order to analyze the influence of the position relationship between the fault and the tunnel on the water inrush, the fault is regarded as a constant head boundary, the bounded aquifer is transformed into an unbounded problem by the reflection method, and a simplified calculation model of the tunnel water inrush is constructed. Based on the theory of groundwater mechanics, Darcy’s law, and the linear superposition principle, the calculation expressions of water inflow and structural external water pressure are derived, and degradation analysis is performed. The correctness of the model is verified by numerical simulation and field test data. Afterward, the sensitivity of the characteristic parameters is studied, and the influence mechanism of the grouting structure and faults on the tunnel water gushing is discussed. The research results show that in order to ensure the safety of the secondary support structure of the tunnel, appropriate grouting circle thickness and a permeability coefficient should be set, and the permeability coefficient of the secondary support structure should be appropriately increased. When the seepage is stable, the tunnel water inflow will increase nonlinearly with the increase of the fault dip, and the sensitivity will gradually increase; when the fault dip is fixed, with the increase of the distance from the tunnel, the restriction of the fault on the tunnel is weakened, and the water inflow decreases continuously. In the case project, the theoretical and measured water inflows of the unfaulted section, single-faulted section, and combined-faulted section differ by 13.36%, 12.79%, and 10.85%, respectively. The difference between the theoretical value and the measured value of the outer edge water head height of the secondary support structure was 10.7%, 10.51%, and 13.87%, respectively. The research results can provide a theoretical basis for the calculation and structural design of tunnels in water-rich fault areas.

Hydrogeological Conceptual Model in the Middle of Randublatung Groundwater Basin

Randublatung groundwater basin is one of the groundwaters basins with massive utilization of groundwater pumping. However, the knowledge of the comprehensive hydrogeological system in this groundwater basin is limited, so this research aims to determine a comprehensive hydrogeological conceptual model of the Randublatung groundwater basin. The methodology was conducted by collecting secondary and primary data of deep and shallow wells to evaluate boundaries of pattern and direction of groundwater flow and develop the aquifer system’s geometry. The result shows that the groundwater flow boundaries are Grogol River in the west, Wado River in the East, Bengawan Solo river in the South as a river boundary, and Rembang Mountains in the North as a constant head boundary. Therefore, groundwater flows from the hills area to the Bengawan Solo River and the north as the river’s flow. Based on the log bor evaluation, the aquifer system of the study area consist of an unconfined aquifer with a maximum thickness of 20 m and three layers of confined aquifers with thickness vary between 8 to 60 m. the hydraulic conductivity of the aquifers depends on the aquifer’s lithology range from sand, gravel, limestone, and sandstone. This hydrogeological conceptual model provides essential information for numerical groundwater models in the middle of the Randublatung groundwater basin.

RichardsFoam3: A new version of RichardsFoam for continental surfaces hydrogeology modelling

RichardsFoam3 is an updated version of the OpenFOAM® solver RichardsFoam, previously presented in “An open source massively parallel solver for Richards equation: Mechanistic modelling of water fluxes at the watershed scale” by L. Orgogozo, N. Renon, C. Soulaine, F. Hénon, S.K. Tomer, D. Labat, O.S. Pokrovsky, M. Sekhar, R. Ababou, M. Quintard (Comput. Phys. Commun. 185 (2014) 3358-3371, https://doi.org/10.1016/j.cpc.2014.08.004), and in the new version announcement “RichardsFOAM2: a new version of RichardsFOAM devoted to the modelling of the vadose zone” by L. Orgogozo (Comput. Phys. Commun. 196 (2015) 619-620, https://doi.org/10.1016/j.cpc.2015.07.009).This new version includes improvements of memory handling and of on-the-fly control of computations, a better integration in the OpenFOAM® framework, simplifications of the coding of some expressions, as well as new advanced boundary conditions. All together these developments allow to enhance the ease of application of the code to continental surfaces hydrogeology modelling, its computational performances and its readability.The description of the elements contained in this release may be found in the readMe file.Please note that you may also find RichardsFoam3 on the hydrology page of the develop.openfoam.com interface:https://develop.openfoam.com/Community/hydrology/ New version program summaryProgram title: RichardsFoam3CPC Library link to program files:https://doi.org/10.17632/vkr7sd6fhb.1Developer's repository link:https://develop.openfoam.com/Community/hydrology/Licensing provisions: GPLv3Programming language: C++Supplementary material: The full system of equations solved by RichardsFoam3 is presented in the documentation directory of the RichardsFoam3 package, with a numbering that is used in the comments of the main source file RichardsFoam3.C of the solver RichardsFoam3, in order to identify which lines of code are related to which equation.Journal reference of previous version: Comput. Phys. Commun. 196 (2015) 619-620Does the new version supersede the previous version?: YesReasons for the new version: Introducing new functionalities and implementing improvements for ergonomy, computational performances and readabilitySummary of revisions: The new features compared to RichardsFOAM [1] and RichardsFoam2 [2] are the following:(i) better handling of memory use during computation;(ii) possibility of on-the-fly modification of the control parameters of the linearisation procedure;(iii) new boundary conditions to be compiled along with the solver itself, and dedicated to the simulation of rain infiltration (rainFallFlux) or no infiltration (noFlux) conditions while allowing exfiltration with OpenFOAM® stand-alone (i.e. without mandatory use of swak4foam as it was the case in RichardsFoam2 [2]);(iv) Computation of the field of piezometric head along computation. NB: in the demonstration cases, a way to implement a constant piezometric head boundary conditions with OpenFOAM is proposed.(v) new functions that allow to build seasonally variable boundary conditions easily;(vi) use of postprocessing procedures with OpenFOAM® stand-alone (i.e. without mandatory use of swak4foam as it was the case in RichardsFoam2 [2]);(vii) several other minor rewritings/cleanings of the code.Nature of problem: This software solves the non-linear three-dimensional transient Richards equation, which is a very popular model for water transfer in variably saturated porous media (e.g.: soils). It is designed to take advantage of the massively parallel computing performance of OpenFOAM®. The goal is to be able to model natural hydrosystems on large temporal and spatial scales.Solution method: A mixed implicit (FVM in the object oriented OpenFOAM framework) and explicit (FVC in the object oriented OpenFOAM® framework) discretization of the equation with a backward time scheme is coupled with a linearization method (Picard algorithm). Due to the linearization loop the final solution of each time step tends towards a fully implicit solution. The implementation has been carried out with a concern for robustness and parallel efficiency.

Ensemble smoother with multiple data assimilation to simultaneously estimate the source location and the release history of a contaminant spill in an aquifer

The source location and the time history of a pollutant released in an aquifer are very relevant information for the design of effective remediation strategies. Usually, their identification requires solving an inverse problem when the only available information about the groundwater contamination event is a sparse set of concentration data collected in the aquifer at a few points downstream from the source. Here, a novel approach is proposed to solve the inverse problem: the use of the Ensemble Smoother with Multiple Data Assimilation (ES-MDA) in the context of source contamination identification. This method is used for the simultaneous determination of the time history and the source location of a pollutant release based on observed concentration data and a calibrated numerical model of groundwater flow and mass transport in the aquifer. The ES-MDA is demonstrated in two case studies. The first one is based on an analytical solution of the flow and transport equations, aimed at the estimation of the source location and the release history of a nonreactive pollutant spreading in a two-dimensional homogeneous aquifer from a point source. For this case, different alternatives are considered for the spatial distribution of the observation points, the concentration sampling frequency, the ensemble size and the use of covariance localization and covariance inflation techniques in the formulation of the smoother. The purpose of this case is to test the new approach, analyze its performance and also to identify the conditions that render the problem ill-posed and, therefore, without solution; also, in this case, a new spatiotemporal iterative localization is presented. In the second case study, we use real data collected in a laboratory sandbox that reproduces a vertical cross-section of an unconfined aquifer with two-dimensional quasi-parallel flow between constant-head boundaries. The results show that the location, time and number of observations, the ensemble size and the application of covariance localization and covariance inflation techniques have an impact on the final solution. A well-designed monitoring network and the application of covariance corrections improve the performance of the ES-MDA and help avoiding ill-posedness and equifinality. The application to laboratory data validates the potential of ES-MDA to simultaneously estimate the time history and the source location of a pollutant released in groundwater in real cases.

On Inflow to a Tunnel in a Fractured Double-Porosity Aquifer.

Inflow to a tunnel is a great public concern and is closely related to groundwater hydrology, geotechnical engineering, and mining engineering, among other disciplines. Rapid computation of inflow to a tunnel provides a timely means for quickly assessing the inflow discharge, thus is critical for safe operation of tunnels. Dewatering of tunnels is another engineering practice that should be planned. In this study, an analytical solution of the inflow to a tunnel in a fractured unconfined aquifer is obtained. The solution takes into account either the spherical or slab-shaped matrix block and the unsteady state interporosity flow. The instantaneous drainage water table and anisotropic hydraulic conductivities of the fractures network are also considered. Both uniform flux and uniform head boundary condition are considered to simulate the constant head boundary condition in the tunnel. The effects of the hydraulic parameters of the fractured aquifer on the inflow variation of the tunnel are explored. The application of the presented solution to obtain the optimum location and discharge of the well to minimize the inflow to a tunnel is illustrated.

Interpretation of Pumping Tests in Heterogeneous Aquifers with Constant Head Boundary.

This paper investigates the impact of heterogeneity of the transmissivity field on the interpretation of steady-state pumping test data from aquifer systems delimited by constant head boundaries such as aquifers adjacent to lakes or rivers. Spatially variable transmissivity fields are randomly generated and used to simulate the drawdown due to a pumping well located at different distances from a constant head boundary. The steady-state drawdown simulated at different observation wells are then interpreted using the Hantush method (Hantush 1959). The numerical simulations show that, in contrast to the case of infinite aquifer domains, the interpreted transmissivity varies depending on well locations and the separation distance between pumping well and boundary relative to the correlation length. The ensemble-averaged estimated transmissivity varies between the geometric mean and the arithmetic mean, and can even exceed the arithmetic mean in a narrow domain adjacent to the boundary. It approaches the geometric mean of the underlying transmissivity field only if the distance between the pumping well is more than 20 times the characteristic length of the transmissivity field.

The Effects of Fault-Zone Cementation on Groundwater Flow at the Field Scale.

Fault zones are an important control on fluid flow, affecting groundwater supply, contaminant migration, and carbon storage. However, most models of fault seal do not consider fault zone cementation, despite the recognition that it is common and can dramatically reduce permeability. In order to study the field-scale hydrogeologic effects of fault zone cementation, we conducted a series of aquifer pumping tests in wells installed within tens of meters of the variably cemented Loma Blanca Fault, a normal fault in the Rio Grande Rift. In the southern half of the study area, the fault zone is cemented by calcite; the cemented zone is 2-8 m wide. In the center of the study area, the cemented fault zone is truncated at a buttress unconformity that laterally separates hydrostratigraphic units with a ∼40X difference in permeability. The fault zone north of the unconformity is not cemented. Constant rate pumping tests indicate that where the fault is cemented, it is a barrier to groundwater flow. This is an important demonstration that a fault with no clay in its core and similar sediment on both sides can be a barrier to groundwater flow by virtue of its cementation; most conceptual models for the hydrogeology of faults would predict that it would not be a barrier to groundwater flow. Additionally, the lateral permeability heterogeneity across the unconformity imposes another important control on the local flow field. This permeability discontinuity acts as either a no-flow boundary or a constant head boundary, depending on the location of pumping.

Groundwater Circulation Well for Controlling Saltwater Intrusion in Coastal aquifers: Numerical study with Experimental Validation

Saltwater intrusion into coastal aquifers has become a prominent environmental concern worldwide. As such, there is a need to prepare and implement proper remediation techniques with careful planning of freshwater withdrawal systems for controlling saltwater intrusion in coastal marine and estuarine environments. This paper investigates the performance of groundwater circulation well (GCW) in controlling saltwater intrusion problems in unconfined coastal aquifers. The GCWs have been established as a promising in-situ remedial technique of contaminated groundwater. The GCW system creates vertical circulation flow by extracting groundwater from an aquifer through a screen in a single well and injecting back into the aquifer through another screen. The circulation flow induced by GCW force water in a circular pattern between abstraction and recharge screens and can be as a hydraulic barrier for controlling saltwater intrusion problem in coastal aquifers. In this study, an effort has been made to investigate the behavior of saltwater intrusion dynamics under a GCW. An experiment has been conducted in a laboratory-scale flow tank model under constant water head boundary conditions, and the variable-density flow and transport model FEMWATER is used to simulate the flow and transport processes for the experimental setup. The evaluation of the results indicates that there is no further movement of saltwater intrusion wedge towards the inland side upon implementation of GCW, and the GCW acts as a hydraulic barrier in controlling saltwater intrusion in coastal aquifers. The present study reveals the GCWs system can effectively mitigate the saltwater intrusion problem in coastal regions and could be considered as one of the most efficient management strategies for controlling the problem.

Identification of groundwater basin shape and boundary using hydraulic tomography

Shapes and boundary types of a groundwater basin play essential roles in the analysis of groundwater management and contaminant migration. Hydraulic tomography (HT), a recently developed new approach for high-resolution characterization of aquifers, is not only an inverse method but a logical strategy for collecting non-redundant hydraulic information. In this study, HT was applied to synthetic 2-D aquifers to investigate its feasibility to map the irregular shapes and types of the aquifer boundaries. We first used the forward model of VSAFT2 to simulate hydraulic responses due to HT surveys in the aquifer with irregular geometry and predetermined constant head conditions at some boundaries, and no-flow conditions at others. The SimSLE (Simultaneous Successive Linear Estimator) inverse model in VSAFT2 was then used to interpret the simulated HT data to estimate the spatial distribution of hydraulic properties of the aquifer using a domain with a wrong geometry surrounded by boundaries of a constant head condition. The inverse modeling experiment used steady-state and transient-states data from the HT forward simulations, and it used the same monitoring network as in the aquifer with irregular geometry to assess the ability of HT for detecting types and shapes of the boundary as well as heterogeneity in the aquifer. Results of the experiment show that no-flow boundaries, which were incorrectly treated as constant head boundaries in inverse models, were portrayed as low permeable zones of the aquifer near the boundaries. Overall, the results show that HT could delineate not only the irregular shape of the aquifer in general but also heterogeneity in the aquifer. Improvements of the estimation with prior information of transmissivity and storage coefficient was also investigated. The study shows that using homogeneous initial guess parameters resulted in a slightly better estimate than others. Moreover, this study employs Monte Carlo simulations to ensure statistically meaningful conclusions.

Semi-analytical solutions of discharge variation of a qanat in an unconfined aquifer subjected to general areal recharge and nearby pumping well discharge

Qanat is a type of drain that extract water from aquifers by gravity. Significant amount of fresh water used in Middle East and other parts of the world are supplied by qanats. Despite their importance, discharge variation of these type of wells received almost no attention. The aim of this research is to obtain a Laplace domain solution of discharge variation of a qanat installed in an anisotropic unconfined aquifer subjected to arbitrary areal recharge and nearby pumping well(s) discharge. A new semi-analytical solution of drawdown is obtained first to implement the effects of arbitrary areal recharge and nearby pumping well(s) using the principle of superposition. Then, the discharge variation solution of the qanat is obtained from the drawdown solution. To establish a constant-head boundary condition at the qanat periphery, the qanat is discretized into several segments. The results of this study are presented in dimensionless discharge-dimensionless time curves. The effects of hydraulic as well as geometric parameters on the discharge variation of the qanat due to arbitrary areal recharge, falling of water table from its initial position and discharge of nearby wells are explored. We also investigate the influences of distance and screen depth and location of the nearby well on the discharge variation of the qanat. The results of this study can be utilized for multiple purposes: 1) to predict discharge of qanat in response to rainfall and nearby pumping well(s); 2) to estimate the aquifer parameters using hydrograph of the qanat; 3) to determine optimal location and pumping pattern of the nearby wells to minimize their influences on the discharge of the qanat; 4) to calculate water budget of aquifers drained by a qanat. The equation presented in this work can also be used to estimate discharge of a horizontal drain installed in cropland subjected to arbitrary irrigation pattern.

Internal fluctuations in green roof substrate moisture content during storm events: Monitored data and model simulations

Understanding how the moisture content in a green roof substrate varies during a storm event is essential for accurately modelling runoff detention. In this paper, a green roof test bed installed with moisture probes at three depths was used to understand how moisture content varies during storms. Detailed studies were conducted on five selected storm events. Physical characterisation tests and field-data based calibrations were performed to acquire the model parameters. Two alternative detention models, based on Reservoir Routing and Richard’s Equation, were validated against the measured green roof runoff and temporary moisture storage data. Once the moisture content exceeds local field capacity, its response at different depths occurs simultaneously during storms, although the recorded data indicate a vertical gradient in the absolute values of local field capacity. Both Reservoir Routing and Richard’s Equation can provide reasonable estimations of the runoff and the vertical moisture content profiles, although Richard’s Equation exhibited stronger vertical water content gradients than were observed in practise. The vertical water content profile is not sensitive to the soil water release curve, although the hydraulic conductivity function influences both the vertical water content profile and runoff rate. The modelled results are highly sensitive to the bottom boundary condition, with a constant suction head boundary condition providing a more suitable option than a free drainage boundary condition or a seepage boundary condition.

In-situ Observation and Nitrate-N Load Assessment in Madhubani District, Bihar, India

Abstract Fertilizers may leach through the vadose zone and eventually reach groundwater in agriculturally intensive areas. Thus, the main focus of this study was to investigate Nitrate-N load and vulnerability of groundwater resources using in-situ observed hydrogeological data. Soil water flow and contaminant transport equation was numerically simulated using HYDRUS 1D for constant head and atmospheric top boundary conditions. Sub-surface materials were distributed based on the lithologs of the target area. Observed water table locations were considered as bottom boundary condition to respective numerical domain. The time taken by Nitrate-N to reach groundwater table was considered to estimate vulnerability index. The results show that Nitrate-N load is higher in constant head boundary conditions than atmospheric boundary conditions. The eastern part of the study area shows high vulnerability than northern part followed by western part. In-situ observed nitrate concentrations were well matched with simulated results. The high vulnerability in eastern and northern part is due to alluvial sandy lithologs and very shallow groundwater table. These findings are in line with the observed low water table depths, less runoff, and higher hydraulic conductivity of the vadose zone material in these area. In western part, forest cover dominated land use causes low pollution vulnerabilities to groundwater resources. This study may help to frame agricultural and soil-water conservation practices with more sustainable remedial techniques.