Groundwater Flow Conditions Research Articles

High-Resolution Integrated Transport Model for Studying Surface Water-Groundwater Interaction.

Transport processes that lead to exchange of mass between surface water and groundwater play a significant role for the ecological functioning of aquatic systems, for hydrological processes and for biogeochemical transformations. In this study, we present a novel integral modeling approach for flow and transport at the sediment-water interface. The model allows us to simultaneously simulate turbulent surface and subsurface flow and transport with the same conceptual approach. For this purpose, a conservative transport equation was implemented to an existing approach that uses an extended version of the Navier-Stokes equations. Based on previous flume studies which investigated the spreading of a dye tracer under neutral, losing and gaining flow conditions the new solver is validated. Tracer distributions of the experiments are in close agreement with the simulations. The simulated flow paths are significantly affected by in- and outflowing groundwater flow. The highest velocities within the sediment are found for losing condition, which leads to shorter residence times compared to neutral and gaining conditions. The largest extent of the hyporheic exchange flow is observed under neutral condition. The new solver can be used for further examinations of cases that are not suitable for the conventional coupled models, for example, if Reynolds numbers are larger than 10. Moreover, results gained with the integral solver provide high-resolution information on pressure and velocity distributions at the rippled streambed, which can be used to improve flow predictions. This includes the extent of hyporheic exchange under varying ambient groundwater flow conditions.

Shallow urban aquifers under hyper-recharge equatorial conditions and strong anthropogenic constrains. Implications in terms of groundwater resources potential and integrated water resources management strategies

Humid equatorial regions are recognized as the least documented in term of hydrogeological functioning of aquifers despite the fact that they house a lot of developing countries and that groundwater is often the main water resource. Regarding this aspect, a study was conducted in sub-Saharan Africa, focusing on the Mio-Pliocene aquifer in Douala megacity (Cameroon) which is the rainiest city in West-Africa (about 4000 mm/year) with one of the greatest demographic growth rate of the African continent. Firstly, groundwater recharge rate has been calculated through water balance and Water Table Fluctuation methods. Results show that the aquifer is characterized by a high recharge of 600–760 mm/year. Then infiltration process and groundwater flow conditions have been examined by combining hydrogeological and isotopic methods. Rainwater infiltrated is recycled in the vadose zone through plants roots transpiration and groundwater flows with a Darcy velocity of 5 m/day. From the recharge area to the estuary, the mineralization increases controlled by anthropogenic activities and water-rocks interactions which are amplified by the residence time and accelerated by the hot and humid climate of Douala. The paper ends with the determination of natural background levels (NBLs) and threshold values (TV) of chemical components in groundwater to assess the contamination for different flow paths. This multi-proxy study and the establishment of NBLs and TV can be beneficial to improve groundwater resources management. Moreover, the conceptual model provided in this study could be used as a reference for porous aquifers submitted to high rainfall amount.

Baseflow Age Distributions and Depth of Active Groundwater Flow in a Snow‐Dominated Mountain Headwater Basin

AbstractDeeper flows through bedrock in mountain watersheds could be important, but lack of data to characterize bedrock properties limits understanding. To address data scarcity, we combine a previously published integrated hydrologic model of a snow‐dominated, headwater basin of the Colorado River with a new method for dating baseflow age using dissolved gas tracers SF6, CFC‐113, N2, and Ar. The original flow model predicts the majority of groundwater flow through shallow alluvium (<8 m) sitting on top of less permeable bedrock. The water moves too quickly and is unable to reproduce observed SF6 concentrations. To match gas data, bedrock permeability is increased to allow a larger fraction of deeper and older groundwater flow (median 112 m). The updated hydrologic model indicates interannual variability in baseflow age (3–12 years) is controlled by the volume of seasonal interflow and tightly coupled to snow accumulation and monsoon rain. Deeper groundwater flow remains stable (11.7 ± 0.7 years) as a function mean historical recharge to bedrock hydraulic conductivity (R/K). A sensitivity analysis suggests that increasing bedrock K effectively moves this alpine basin away from its original conceptualization of hyperlocalized groundwater flow (high R/K) with groundwater age insensitive to changes in water inputs. Instead, this basin is situated close to the precipitation threshold defining recharge controlled groundwater flow conditions (low R/K) in which groundwater age increases with small reductions in precipitation. Work stresses the need to explore alternative methods characterizing bedrock properties in mountain basins to better quantify deeper groundwater flow and predict their hydrologic response to change.

Thermal response test analysis for U-pipe vertical borehole heat exchangers under groundwater flow conditions

Conventional models used in the analysis of thermal response test data only consider conduction as heat transfer mechanism. In cases where presence of groundwater is detected, convection heat transmission plays an important role, so its influence must be determined in the calculation of the effective thermal conductivity, usually overestimated in these situations, increasing its value the higher the power injected and the time elapsed. In this work, based on the data collected in a borehole located at UPV (València) in which have been carried out three thermal response tests with different characteristics, has been implemented a variation of the finite line source model introducing an expression for the effective thermal conductivity formed by two terms, one static unaffected by underground flow and another dynamic that depends on time. Analyzing the data in the model developed and in the finite line source and infinite line source models, the results show that the new model estimates accurately the conductivity value unaffected by underground flow regardless the power injected or the time elapsed in the test, with differences between the results obtained in the analysed tests and average thermal conductivity of 1,4%, compared to the conventional models in which this difference is 27%.

Evaluation of arsenic sorption performance using dendritic anatase and polycrystalline rutile nano-TiO2 for environmental applications

Two synthetic nano-TiO2-based materials, aggregated dendritic anatase nano-TiO2 and polycrystalline rutile nano-TiO2 attached to the surface of SiO2, were analyzed and compared for geo-environmental engineering applications. Characterization of crystal structure, purity, and morphologic, microscopic features of the materials were examined by X-ray powder diffraction, X-ray fluorescence, and scanning electron microscope, respectively. Arsenic removal rates/efficiencies were compared between the two materials in different settings for laboratory batch experiment. The adsorption curve on arsenic was obtained. Subsequently, different concentrations of arsenic solutions were injected in batches at different flow rates 0.67, 0.83, 1.00, 1.25, 1.67, 2.50, 5.00, and 10.00 ml/min to simulate field conditions. Results show that both of TiO2-based materials demonstrate outstanding capabilities for arsenic removal. Removal rates are 83% (± 0.025) and 95% (± 0.024) for aggregated TiO2, while 82% (± 0.031) for 93% (± 0.013) for attached TiO2. Results suggest that attached form of TiO2 is more effective for arsenic removal under fast groundwater flow condition, while aggregated form TiO2 can be suitable for high arsenic concentration and low water flow rate. Both materials are considered cost-effective as both can be recovered and reused after regeneration process.

Modelling of the Complex Groundwater Level Dynamics during Episodic Rainfall Events of a Surficial Aquifer in Southern Italy

We analyzed the complex dynamics that are involved the groundwater level variations due to the episodic rainfall supply in the Ionian coastal plain surficial aquifer located in Southern Italy. In this aquifer, as a consequence of the particular hydrogeological framework, both direct and lateral recharge mechanisms coexist. Hence, the dynamics of groundwater level variations are quite complex and strongly non-linear. Our focus was essentially on the short-term behavior of groundwater levels, with a specific analysis on episodic rainfall events. To model these dynamics, due to the presence of the preferential pathways in the infiltration processes, a kinematic dispersion wave model was used. Specifically, a one-dimensional and non-linear particle-based numerical model was developed. It uses ideal particles with constant water volume travel, according to celerity and hydraulic dispersion, to simulate the infiltration rate wave through the vadose zone. The infiltration rate that reaches the water table represents the input function to evaluate the aquifer groundwater level fluctuations. As a consequence of the special lithological and storage capacity characteristics of the surficial layers, groundwater flow conditions change from unconfined to confined. The developed model analyzes the direct groundwater supply under natural conditions, including episodic rainfall, and it has been validated using a high-resolution time series of rainfall data and groundwater level obtained from the monitoring station Terra Montonata.

Significance of basin asymmetry and regional groundwater flow conditions in preliminary geothermal potential assessment – Implications on extensional geothermal plays

Abstract Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.

Modeling Hydrologic Controls on Particulate Organic Carbon Contributions to Beach Aquifer Biogeochemical Reactivity

AbstractThe intertidal zone of beach aquifers hosts biogeochemical transformations of terrestrially derived nutrients that are mediated by reactive organic carbon from seawater infiltration. While dissolved organic carbon is often assumed the sole reactive organic carbon component, advected and entrapped particulate organic carbon (POC) is also capable of supporting chemical reactions. Retarded advection of POC relative to groundwater flow forms pools of reactive carbon within beach sediments that support biogeochemical reactions as dissolved solutes move across them due to transient groundwater flow. In this work, we simulate the contribution of POC to beach reactions and identify parameters that control its relative contribution using a groundwater flow model (SEAWAT) and reactive transport model (PHT3D). Results show transient contributions of POC to denitrification, as the spatial extent of the saline circulation cell varies over time due to changing hydrologic factors. A decrease in POC retardation and an increase in tidal amplitude during POC deposition resulted in POC expansion, which increased the relative contributions of POC to beach reactivity. Decreased hydraulic conductivity and increased tidal amplitude post‐deposition decreased the utilization of POC for denitrification by allowing the oxic, saline water to completely encompass the pool of POC. Results highlight that POC is an intermittently utilized source of carbon that displays complex spatial relationships with groundwater flow conditions and overall beach biogeochemistry. This work demonstrates that POC may be a periodically important but overlooked contributor to biogeochemical reactions in carbon‐poor beach aquifers.

Multi-decadal dating of surface slope movements in forested DSGSD areas of the European Alps: detecting precipitation triggering factors

ABSTRACT An integrated approach including dendrometric and dendrogeomorphological analysis, geotechnical monitoring and numerical modeling was established on a reactivating landslide in a forested Deep-Seated Gravitational Slope Deformation (DSGSD) area in Valtellina, Italy, in order to define the distribution of surface displacements in space and time as well as to identify the triggering factors (i.e. precipitation and a recent road tunneling). By means of a normalized difference eccentricity index (EI), we dated with annual resolution the surface displacements occurred over the period 1980–2016: the instability signals spread from the upper portion of the landslide (C) in 1980s to the middle section (B) especially in the 2000s, when they also occurred in the lowest portion (A). Mean Absolute EI (MAEI index) highlighted the intensity of the displacement signals, whereas changes in the MAEI series (dMAEI index) allowed to find correspondences between precipitation input and tree-ring eccentricity. A diagnostic test applied to these correspondences showed an overall accuracy of 0.74 and allowed to determine the precipitation threshold values acting as triggering factors. Topographic monitoring networks in 2016 revealed displacements <1 mm in the upper portion of the landslide, whereas the middle and lowest portion displacements were ranging 1–10 mm. The inclinometric probes confirmed the same trend for in-depth displacements, pointing out multiple sliding surfaces. A numerical stress-strain model, integrating information both from the instrumental and the dendrochronological approaches, provided information on the slope dynamics and its controlling factors, including groundwater flow conditions and the recent tunneling, thus allowing a comprehensive assessment of the geomorphological hazard.

Constant-head and variable-head injection tests for determining the hydraulic parameters of an aquitard

Although specific storage (SS) is a crucial parameter for characterizing the dynamic water-release process in an aquitard, the Hvorslev analysis method is only capable of estimating the hydraulic conductivity (K), rather than SS. The Hvorslev method is based on an assumption of steady-state flow and uses the falling-head test. Considering the elastic water-release effect in an aquitard and the actual groundwater flow, two mathematical unsteady-state groundwater flow models (i.e., the constant-head and variable-head models), describing the head distribution are presented for a constant-head injection test (CHIT) and variable-head injection test (VHIT) performed in a multi-layered aquifer-aquitard system. The analytical solutions for the models are derived by Fourier transforms to estimate K and SS. The obtained K and SS values from the CHIT and VHIT were generally consistent, although the VHIT is recommended in practice. For the VHIT, estimating K using the Hvorslev analysis method under steady-state groundwater flow conditions resulted in a small relative error compared to the obtained result from the variable-head model. It was demonstrated that a certain relation existed between the constant-head and variable-head methods when the drawdown rate was lower than 1%, and so the constant-head method was applied to the VHIT data to determine K and SS. The synthetic error in the parameters was smaller than 10%, which indicated that the methods could be used interchangeably under these circumstances, thus simplifying the hydraulic parameter estimation process.

Analytical Solutions of Intermittent Transient Groundwater Pumping Cost

Abstract In this paper, we have studied ways to minimize the cost of stepwise or intermittent pumping from a system of wells under transient groundwater flow conditions. We take into account infini...

Stochastic analysis of the groundwater velocity field and implications for contaminant transport within the Ga East and Adentan municipalities, Ghana.

The hydrogeological systems of the Ga East and Adentan Districts of the Greater Accra Region, Ghana were studied using a numerical model. Historical hydrogeological and groundwater monitoring data on twenty boreholes were used in conceptualising the hydrogeological system. The objective was to estimate the aquifer hydraulic conductivity and recharge, and also simulate the velocity field to assess the impact of contaminant transport within the study area. A steady-state model was developed depicting the groundwater flow conditions of the terrain. A single aquifer system (quartzite-schist formation) has been identified. The aquifer hydraulic conductivity estimates indicate that over 90% of the terrain is lower than 15.0 m day−1. The observed outliers are attributable to the fractured and jointed quartzites. The effective aquifer recharge through precipitation for this study ranges between 2.70×10−5m day−1 and 8.10×10−5 m day−1, representing 1.2%–3.6% of the average rainfall records per year in the area. Cases of local and intermediate flow systems, and potential recharge areas were identified. The estimated velocity field ranges from 0.002 to 11.2 m day−1, with over 90% of the area having velocities below 0.85m day−1. The spatial distribution of the velocity field ties in well with the hydraulic conductivity field observed for the terrain. The estimated velocity field makes contamination transport significant in the domain. For instance, contaminants leached into the aquifer zone through recharge by rainfall from the landfill site at Pantang will travel at approximately 0.85 m day−1 towards Oyarifa, Teiman and Ayimensa communities along an identified flowpath. Seven principal groundwater flowpaths have been identified using the particle tracking technique. The travel times along the flowpaths from recharge to discharge locations ranges from 7 years to 833 years. Stochastic simulations carried out on the calibrated model indicate that the model is unique with respect to the aquifer recharge, hydraulic conductivity and hydraulic head.

Repeated Subsurface Thermal Profiling to Reveal Temporal Variability in Deep Groundwater Flow Conditions

AbstractReliably quantifying groundwater fluxes to and from confined aquifers in sedimentary basins is increasingly recognized as a critical challenge that impedes sustainable groundwater management. One approach to quantify such fluxes is through the analysis of deep (e.g., &gt;50 m) borehole thermal profiles penetrating through aquifer‐aquitard systems. Recently developed methods to interpret such data exploit the relationship between vertical groundwater flow and the downward propagation of surface temperature disturbances resulting from climate warming. In this note, we advance beyond prior studies that assumed steady‐state groundwater flow by demonstrating how hydrogeological regime shifts on decadal time scales can be quantitatively inferred from temperature‐depth profiles (TDPs). We use a set of repeated temperature‐depth profiles from one site in an unconsolidated sedimentary aquifer system, recorded in 1980 and 2016/2018 to tentatively infer a minimum of a threefold increase in groundwater downwelling to deeper aquifers (i.e., from 100 to 350 mm/year). The enhanced flux likely results from intensified, deep groundwater abstraction in the vicinity since the mid‐1980s. We reach this conclusion through analyzing the occurrence and downward propagation of the minimum temperature in the profiles as well as the temporal trend in deeper groundwater temperatures. We conclude that repeated temperature‐depth profiles can be suitable to archive hydrogeological changes. Our results provide the impetus for more systematic collection of present‐day TDPs to provide a historical benchmark from which to assess future groundwater flow alterations, especially in areas that lack traditional aquifer monitoring via hydraulic head measurements.

Impact of Lateral Groundwater Flow and Subsurface Lower Boundary Conditions on Atmospheric Boundary Layer Development over Complex Terrain

AbstractCredible soil moisture redistribution schemes are essential to meteorological models, as lower boundary moisture influences the balance of surface turbulent fluxes and atmospheric boundary layer (ABL) development. While land surface models (LSMs) have vastly improved in their hydrologic representation, several commonly held assumptions, such as free-draining lower boundary, one-dimensional moisture flux, and lack of groundwater representation, can bias the terrestrial water balance. This study explores the impact of LSM hydrology representation on ABL development in the Weather Research and Forecasting (WRF) meteorological model. The results of summertime WRF simulations with Noah LSM, characterized by 2-m-thick soil and one-dimensional flow, are shown for a domain in the Colorado Rocky Mountain headwaters region. A reference WRF simulation is compared to 1) the same model with soil moisture initialized by the hydrologic model ParFlow; 2) a deep, free-draining simulation; and 3) WRF coupled to ParFlow, a three-dimensional, integrated groundwater-surface water model. Results show that both lateral transport of groundwater and the rate of drainage from the lower soil layer can weaken or reverse the coupling strength between evaporative fraction and ABL over a 5-month summer period. The resulting shifts in low-level moist convection in river valleys and thermally driven airflows yield strengthened anabatic upslope winds and perturbations to regional precipitation.

Effects of upscaling temporal resolution of groundwater flow and transport boundary conditions on the performance of nitrate-transport models at the regional management scale

Managed aquifer recharge and changes in crop type or nutrient management on agricultural lands are promising approaches to address groundwater quality degradation by nitrate. Tools to assess nonpoint-source contaminant transport are needed to better understand the interaction between agricultural management practices and long-term nitrate dynamics in groundwater basins. This study investigates the impact of time-resolution upscaling of groundwater flow stresses (i.e., recharge, pumping, and evapotranspiration rates) on the long-term prediction of nitrate transport at the regional scale. A three-dimensional, monthly transient flow and nitrate-transport model using MODFLOW and MT3D is applied as the reference simulation. The reference model results are compared to temporally upscaled models with (1) upscaled annual-averaged flow and transport stresses and (2) steady-state flow stresses, across different management scenarios. Models with annual-averaged flow and nitrate-loading stresses were found to be the best alternative to the reference model. However, employing a steady-state flow field to parameterize transient transport models, using a time series of spatially variable annual total contaminant loading, provides a useful alternative to predict the trend and variability of nitrate-concentration breakthrough curves at wells across the regional scale and to differentiate the effects of various agricultural management scenarios, if the history of the source contaminant mass is known. The difference between concentrations resulting from steady-state-flow versus transient-flow models is less than 2 mgN/L for nearly 75% of shallow groundwater cells in the model. However, the steady-state-flow-model-based transport simulation does not capture short-term oscillations of nitrate concentrations in pumping wells at the local scale.

Hydrothermal interactions in energy walls

Energy geostructures (EGs) employ heat exchangers embedded in concrete geostructures, such as piles, walls, tunnels, and sewers. In this study, energy walls (EWs) are studied with an emphasis on the following objectives: (1) to understand the fundamentals of hydrothermal interactions acting in the vicinity of EWs caused by groundwater seepage in saturated soil; (2) to highlight hydraulically induced thermal effects and their consequences on the thermal performance of EWs. Extensive three-dimensional hydrothermal finite element analyses are performed considering two groundwater flow conditions: perpendicular and parallel to the EW. The thermal activation of the geostructure locally modifies the flownet with respect to the non-isothermal case because of the temperature dependency of the water properties. Mutual interactions between seepage directions and thermal activation are analyzed. Remarkable thermal interactions are detected within the heat exchangers. The thermal behavior of EGs is highly affected by an incorrect evaluation of the hydraulically induced thermal effects, which may result in an overestimation of the thermal behavior. Conversely, an efficient thermal design, which considers such interactions, may increase the thermal potential of EGs.

Three-Dimensional Laboratory Experiments on Fate and Transport of LNAPL under Varying Groundwater Flow Conditions

AbstractVariations in groundwater flow regimes due to direct draining/pumping and surrounding climatic variabilities may significantly affect the spatial and temporal distribution of hydrocarbon co...

Long-Term Temperature Evaluation of a Ground-Coupled Heat Pump System Subject to Groundwater Flow

The performance of ground-coupled heat pump systems (GCHPs) operating under significant groundwater flow can be difficult to predict due to advective heat transfer in the subsurface. This is the case of the Carignan-Salières elementary school located on the south shore of the St. Lawrence River near Montréal, Canada. The building is heated and cooled with a GCHP system including 31 boreholes subject to varying groundwater flow conditions due to the proximity of an active quarry being irregularly dewatered. A study with the objective of predicting the borehole temperatures in order to anticipate potential operational problems was conducted, which provided an opportunity to evaluate the impact of groundwater flow. For this purpose, a numerical model was calibrated using a full-scale heat injection test and then run under different scenarios for a period of twenty years. The heat exchange capacity of the GCHP system is clearly enhanced by advection when the Darcy flux changes from 6 × 10−8 m s−1 (no dewatering) to 8 × 10−7 m s−1 (high dewatering). This study further suggests that even the lowest groundwater flow condition can be beneficial to avoid a progressive cooling of the subsurface due to the unbalanced building loads, which can have important impacts for design of new systems.

Classification of Factors Affecting the Performance of Fully Grouted Rock Bolts with Empirical Classification Systems

Empirical classification systems do not provide details of the factors that affect the performance of fully grouted rock bolts, as they are based on average values. Fully grouted rock-bolt patterns during tunnel-support design are a part of the composite support, and they are functions of rock-mass quality and tunnel span. Various fully grouted rock bolts are used in situ in different environments, along with other tunnel-support materials in static and dynamic environments during tunnel construction. The rock-bolt performances are evaluated through pull-out tests that follow ASTM standards. Several field pull-out tests were conducted on cement and resin grouted rock bolts. Under groundwater flow conditions, inflated steel tube rock bolts were tested and the results were compared with fully grouted rock bolts. Based on field experiments and previous studies, the factors that affect rock bolt performances are divided into five groups with respective sub-factors. Natural parameters cannot be controlled to ensure safety, economy, and stability in tunnels. The controllable factors, too, can be varied only within a practical range. In conclusion, the factors investigated here should be considered with the empirical support pattern of rock-mass classification systems for safe and economical design.

Ground environment characteristics during the operation of GWHP considering the particle deposition effect

Groundwater heat pump (GWHP) systems are central heating and cooling systems that utilize groundwater heat. With the rapid development of this technology in China, it has become imperative to study the changes in the ground environment, including the flow features, heat transfer characteristics and clogging caused by long-term recharge, during the operation of GWHP systems. In this paper, a mathematical model considering the effect of particle deposition was proposed to describe a GWHP system based on the typical geological and hydrogeological conditions (i.e., a dual-structure strata) in Wuhan, China. During research on a GWHP engineering project in the Baibuting Garden community, four groundwater flow conditions (including no flow, forward flow, reverse flow and cross flow) and two typical flow modes (continuous and flushing modes) were considered. The groundwater temperature and flow rate were measured through measuring wells, and a comparison between theoretical and actual values shows that this model can provide an easy yet effective way to describe GWHP engineering. The seepage and temperature fields both display periodic trends under the continuous flow mode and can be significantly affected by well flushing. The central area is marginally influenced by groundwater flow when compared with the surrounding areas; for instance, the temperature fluctuation at MW3 can reach 8.2 °C, while the fluctuation reaches 2.9 °C at MW1. Particle deposition can affect the parameters of the ground environment; we find considerable correspondence between the concentration of deposited particles and the porosity. Moreover, both the concentration of deposited particles and the porosity change by a large margin after flushing, especially in regions around pumping wells (the concentration of deposited particles can fluctuate by 108 g/L, and the porosity can change by 0.055).