Vertical Hydraulic Conductivity Research Articles

Confined seepage analysis of saturated soils using fuzzy fields

Seepage refers to the flow of water through porous materials. This phenomenon has a crucial role in dam, slope, excavation, tunnel, and well design. Performing seepage analysis usually is a challenging task, as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon. However, at the same time, the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution. In this context, so-called non-traditional approaches for uncertainty quantification (such as intervals and fuzzy variables) offer an interesting alternative to classical probabilistic methods, since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available. Therefore, the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils, where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields. This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers. In fact, it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component, since they allow one to account for available physical measurements. A case study in confined saturated soil shows that with the proposed framework, it is possible to quantify the uncertainty associated with seepage flow, exit gradient, and uplift force effectively.

Very‐Near‐Field Coseismic Fault Pressure Drop and Delayed Postseismic Cross‐Fault Flow Induced by Fault Damage From the 2018 M6.3 Hualien, Taiwan Earthquake

AbstractEarthquakes can produce rock damage, poroelastic deformation, and ground shaking that modify fault zone hydrogeologic properties. Coseismic and postseismic hydrologic response to the ruptured fault can serve as constraints on hydrogeologic property changes. Here, we document fluid pressure responses to the 2018 M6.3 Hualien, Taiwan earthquake and model the postseismic fault zone hydrology inferred from very‐near‐fault data. Two groundwater wells located ∼180–250 m from the fault damage zone experienced 10–15 m of groundwater level decline followed by a prolonged (>6 months) recovery. Poroelastic models indicate that strain dilation in the fault's hanging wall can produce water level reductions of several meters. However, the model cannot explain groundwater level change in the footwall nor the delayed postseismic recovery, suggesting fault zone damage played a primary role in both the coseismic and postseismic water level reductions. Fluid flow models incorporating the effects of coseismic fault damage on the temporal evolution of hydrologic fault properties show enhanced hydraulic anisotropy after the earthquake. The best‐fit models show that while both vertical hydraulic conductivity and specific storage likely increased within the fault zone, the horizontal hydraulic conductivity is low, suggesting the fault zone behaves as a hydraulic barrier to cross‐fault flow with modeled diffusivities as low as ∼10−3 m2/s. High‐fidelity hydrologic measurements in the very‐near‐field of fault zones (e.g., within a few hundred meters) may be a useful tool to constrain the spatial and temporal evolution of fault zone properties before, during, and after rupture.

Investigating soil properties and their effects on freeze-thaw processes in a thermokarst lake region of Qinghai-Tibet Plateau, China

Soil parameters form the foundation of hydrogeological research and are crucial for studying engineering construction and maintenance, climate change, and ecological environment effects in cold regions. However, the soil properties in the permafrost region of the Qinghai–Tibet Plateau (QTP) remain unclear. Hence, in this study, soil temperature (Ts), volumetric specific heat capacity (C), thermal conductivity (K), thermal diffusivity (D), soil water content (SWC), electric conductivity (EC), vertical (Kv) and horizontal (Kh) saturated hydraulic conductivity, bulk density (ρb), and soil texture near the Qinghai-Tibet Railway were measured, and their effects on the freeze-thaw process were evaluated. The results revealed a predominantly sandy loam soil texture, with Kh and Kv showing strong spatial variability, while the other parameters presented moderate spatial variability. Thermokarst lake had a limited influence on D, C, K, and ρb but significantly reduced Kh and Kv. Groundwater affected SWC, Ts, and EC. The model results showed that all parameters indicated small sensitivities to the maximum thawing depth (MTD), with MTD positively responding to all parameters except for Kv and porosity (ρp). Except for Kh and Kv, all parameters showed high sensitivities to the time from starting to complete freezing (TSCF). TSCF responded positively to C, ρp, and density (ρd) and negatively to K and Kh. This study expanded the quantification of soil properties in the QTP, which can help improve the accuracy of cryohydrogeologic models, thus guiding the construction and maintenance of infrastructure engineering.

Pesticides trapping performance of vegetative filter strips in black soil region, Northeast China: controlled experiments and VFSMOD-W modeling

The Northeast black soil region in China is an important grain-producing area where various pesticides are extensively used to increase grain yields. However, this practice poses serious risks to the ecological health of soil and water systems, necessitating effective measures. Vegetative filter strips (VFS) are commonly used to mitigate agricultural diffuse pollutants, but their efficiency varies across different regions, requiring assessment. This study employed flume experiments, the VFSMOD-W model, and redundancy analysis (RDA) to evaluate the efficacy of VFS in runoff, sediment, and pesticide removal, as well as influencing factors. The results showed that VFS reduced outflow rate of runoff by 8 %–64 % and sediment by approximately 90 %, achieving load removal rates of 61 % and 95 % respectively. Pesticide load removal efficiency ranged from 37 % to 94 %, with higher efficiency for adsorbed pesticides like chlorpyrifos compared to water-soluble ones like atrazine. Interflow and vertical seepage were significant pathways for pesticide transport in VFS, with chlorpyrifos concentrations at 4 %–26 % and atrazine at 20 %–37 % of inflow concentrations. The VFSMOD-W model accurately predicted VFS efficiency (NSE > 0.90), and RDA results indicated that environmental factors could explain 86.7 % of the variation in VFS performance, with soil vertical saturated hydraulic conductivity (VKS) being the most influential factor, followed by rainfall intensity (T), saturated soil water content (OS), initial soil water content (OI), and filter slope for each segment (SOA). Optimizing soil moisture characteristic factors and increasing infiltration are crucial for VFS performance. Applying VFSMOD-W for precise VFS design can help reduce construction costs. In the future, long-term field monitoring and evaluation of VFS efficiency after implementation should be conducted in the black soil region of Northeast China to provide data supporting the improvement of VFSMOD-W simulation accuracy. This will also offer recommendations for the government in formulating VFS configuration schemes.

Delineating aquitard characteristics within a Silurian dolostone aquifer using high-density hydraulic head and fracture datasets

Fractured aquifers are heterogeneous due to the variable frequency, orientation, and intersections of rock discontinuities. A ~100-m-thick Silurian dolostone sequence provides a bedrock aquifer supplying the city of Guelph, Canada. Here, fracture network characteristics and associated influences on hydraulic head were examined using several data types obtained from 24 cored holes in a study that is novel for the quantity and quality of data. High (50–90°) angle joint orientations, heights, and terminations relative to bedding features were determined from acoustic televiewer logs and outcrop scanlines. These data were compared to high-resolution hydraulic head profiles showing head loss over depth-discrete intervals identifying zones with lower vertical hydraulic conductivity. This study reveals that the marl-rich Vinemount Member, traditionally considered the principal aquitard, corresponds to head loss in only 62% of the 24 boreholes. The vertical position of head loss varies across the 90-km2 study area and occurs in any of the lithostratigraphic units of the Lockport Group. Within this sedimentary sequence, aquitards are laterally discontinuous or “patchy” at variable depths and relate to: (1) the frequency of the high-angle joints; (2) shorter joint height; and (3) the type of joint terminations. The head loss occurs in thin (2–2.5 m) intervals where the frequency of the high-angle joints is low. Where a large proportion of small joints cross-cut marl bedding planes, head loss is negligible, suggesting that the vertical hydraulic conductivity is not reduced. Overall, these findings are potentially applicable to assessing aquitard and cap rock integrity in carbonate sedimentary sequences worldwide.

The Effective Vertical Anisotropy of Layered Aquifers.

Many sedimentary aquifers consist of small layers of coarser and finer material. When groundwater flow in these aquifers is modeled, the hydraulic conductivity may be simulated as homogeneous but anisotropic throughout the aquifer. In practice, the anisotropy factor, the ratio of the horizontal divided by the vertical hydraulic conductivity, is often set to 10. Here, numerical experiments are conducted to determine the effective anisotropy of an aquifer consisting of 400 horizontal layers of which the homogeneous and isotropic hydraulic conductivity varies over two orders of magnitude. Groundwater flow is simulated to a partially penetrating canal and a partially penetrating well. Numerical experiments are conducted for 1000 random realizations of the 400 layers, by varying the sequence of the layers, not their conductivity. It is demonstrated that the effective anisotropy of the homogeneous model is a model parameter that depends on the flow field. For example, the effective anisotropy for flow to a partially penetrating canal differs from the effective anisotropy for flow to a partially penetrating well in an aquifer consisting of the exact same 400 layers. The effective anisotropy also depends on the sequence of the layers. The effective anisotropy values of the 1000 realizations range from roughly 5 to 50 for the considered situations. A factor of 10 represents a median value (a reasonable value to start model calibration for the conductivity variations considered here). The median is similar to the equivalent anisotropy, defined as the arithmetic mean of the hydraulic conductivities divided by the harmonic mean.

Improvement of field falling-head test and determination of hydraulic conductivity using Darcy’s equation

This study presents a novel permeameter design for field falling-head tests to determine vertical hydraulic conductivity (K) using Darcy's equation. The design features an open-ended standpipe with two ports for simultaneous measurement of hydraulic heads at both ends of the sediment column, enabling direct estimation of flow rate (q) and hydraulic gradient (i). Flow rate is calculated by differentiating the best-fit curve for water level change above the sediment, and the hydraulic gradient is derived from the head difference between the ports. Laboratory and field tests consistently demonstrated a strong linear relationship between q and i (R2 > 0.999), validating the applicability of Darcy's equation for this new permeameter design. The K values obtained using the proposed method matched those obtained using the Hvorslev equation method. Furthermore, the design allows for continuous measurement of heads after the falling-head permeameter test, facilitating the collection of time series data for the hydraulic gradient. When combined with a pre-determined K value, this enables calculation of time series for the seepage rate across the surface water/sediment interface. To demonstrate this capability, preliminary tests were conducted using commercially-available pressure transducers to monitor heads and obtain seepage time series. The results of these tests are also presented.

Determining peat's vertical hydraulic diffusivity and hydraulic conductivity from naturally occurring hydraulic pressure fluctuations measured at various depths

AbstractThis study presents a method that could be used to assess the in‐situ saturated vertical hydraulic conductivity of deeper and more decomposed peat layers. Deeper peat layers may exhibit very low permeability comparable to clayey sediments, where measurements and sediment sample collection are very difficult. More traditional measurement methods, such as slug‐tests and permeameter tests, have proven difficult to carry out in these conditions, necessitating an alternative method. For surpassing these possible constraints, this paper introduces a field method to quantify vertical hydraulic diffusivity, capitalizing on naturally occurring hydraulic pressure fluctuations measured with buried pressure sensors. The determined diffusivity values are used to calculate vertical hydraulic conductivity of peat using separately measured compressibility and specific storage values. Our research demonstrates the feasibility of using this method to evaluate vertical hydraulic diffusivity in lower peat layers. Calculated diffusivity values, combined with peat compressibility measurements, yield reasonable estimates of vertical hydraulic conductivity for dense fen peat comparable with more widely used in‐situ and laboratory methods. It also shows potential for vertical hydraulic characteristics parametrization in the upper less decomposed and compacted peat layers; however, further research is needed to understand the method's limitations in such conditions. Our approach provides a potential method for measuring in‐situ vertical hydraulic properties of less accessible peat layers, often overlooked, while also providing a way to surpass the scale‐dependency constraints inherent in peatlands' heterogeneous structure. Such information is necessary when studying the hydraulic interactions between groundwater aquifers and peatlands.

Uncertainty assessment of thermal recovery and subsurface temperature changes induced by high-temperature aquifer thermal energy storage (HT-ATES): A case study

High-temperature aquifer thermal energy storage (HT-ATES) systems can store renewable-based or waste heat in the subsurface on a seasonal scale and may thus reduce the carbon footprint of future heat supply systems. Thermal recovery, i.e. the ratio of extracted to injected heat over one cycle, is required in a pre-application assessment because it determines the operational and economic viability of a HT-ATES system. The induced temperature changes in the subsurface are required to obtain the legal permits and are of interest for the design of a monitoring network. However, uncertainty in our knowledge on subsurface hydraulic and thermal parameters translates into uncertainties of the expected thermal recovery and the temperature changes induced during HT-ATES operation. In order to address these uncertainties for a case study in Hamburg, Germany, we use numerical modeling of the coupled thermo-hydraulic processes during the design stage of a HT-ATES system, based on a realistic load curve and the local geological setting of the storage aquifer. An ensemble of 50 scenarios was parameterized based on site-specific parameter uncertainties using Latin hypercube sampling to reflect the global parameter distributions, and the HT-ATES operation was simulated over a period of 26 years in each case. Most of the scenarios show high thermal recoveries with a median of 89 % in the 26th year, with thermal recovery most sensitive to the vertical hydraulic conductivity. The expected temperature distribution is well defined by the ensemble of model simulations, with far-field temperature changes reaching for hundreds of meters and showing greater variability between scenarios than those in the near-field region of the warm HT-ATES well on the tens of meters scale. Locations with large temperature differences between scenarios are identified as suitable for the placement of temperature monitoring wells. The presented work thus contributes directly to the design and permitting of HT-ATES systems and can also be used for uncertainty assessment of future HT-ATES plants and the identification of suitable monitoring setups.

Effect of the spatial distribution of macroinvertebrates in the benthic and hyporheic zones on the vertical hydraulic conductivity of the streambed

Water quality, aquatic habitat, and groundwater recharge, which have a critical impact on the river ecosystem health, are associated with the vertical hydraulic conductivity of streambed (Kv). Macroinvertebrates bioturbation can generate heterogeneity in the benthic and hyporheic zones to influence Kv by particle reworking and burrow construction, which are directly and indirectly related to the physicochemical conditions of sediments. However, understanding how these factors and processes influence Kv and its role is deficient. Here the spatial distribution of benthic macroinvertebrates and its effects on Kv in the Weihe River were investigated. Macroinvertebrate bioturbation had a significant effect on Kv when the biomass was greater than 1 mg/m2, and yet when the biomass exceeded 102 mg/m2, bioturbation had a significant inhibitory effect on Kv as the result of clogging due to the fine sediment particles and secrete mucus produced by benthic Macroinvertebrates. Macroinvertebrate distribution and biomass are often influenced by temperature which could also decrease the fluid viscosity, thus improving Kv. Moreover, the mixed bioturbation mode with the predominated Tubificidae was better than the bioturbation mode of single-type benthic macroinvertebrates in improving sediment permeability. These findings have important implications for revealing the disturbance mechanism of benthic macroinvertebrates on Kv and provide a reliable theoretical basis for the protection and planning of river ecosystems.

2D model of groundwater flow and total dissolved HCH transport through the Gállego alluvial aquifer downstream the Sardas landfill (Huesca, Spain)

The organic pollutants disposed at the Sardas landfill in Sabiñánigo (Huesca, northeastern Spain) by the INQUINOSA lindane factory have reached the Gállego alluvial aquifer and could affect the Sabiñánigo reservoir. The daily oscillations of the reservoir water level produce a tidal effect on the piezometric heads of the aquifer. These oscillations are transmitted in a damped way with a time lag, thus attesting that the silting sediments of the reservoir and the natural silts of the Gállego alluvial are interposed between the reservoir water and the layer of sands and gravels. A 2D finite element groundwater flow and total dissolved hexachlorocyclohexane (HCH) transport model through the Gállego alluvial aquifer is presented here. The flow model was constructed to: (1) Quantify the tidal effect, produced by the daily fluctuations of the reservoir water level on the aquifer; (2) Estimate the hydrodynamic parameters of the layer of sands and gravels; and 3) Estimate the vertical hydraulic conductivity of the silting sediments and silts; and (4) Quantify aquifer/reservoir interactions. The flow model reproduces the dynamics of the tidal effect and attests that groundwater velocity and flow direction changes daily in response to the oscillations of the reservoir level. Model results reproduce the measured well hydrographs and the Darcy velocity derived from tracer tests and confirm the validity of the conceptual model. The transport model of total dissolved HCH simulates the time evolution of the contaminant plume. The computed concentrations of total dissolved HCH and the contaminant mass outflux are very sensitive to changes in the source terms and the distribution coefficient, Kd of HCH. The best fit to the measured HCH plumes in September 2010 and December 2020 is obtained with a Kd ranging from 1 to 3 L/kg. The computed flux of dissolved HCH leaving the Sardas site in 2020 towards the Sabiñánigo reservoir ranges from 0.6 kg/year for Kd = 3 L/kg to 3.1 kg/year for Kd = 1 L/kg. The findings of this study will be most useful for planning and designing remedial and containment actions at the Sardas site and other similar lindane-affected sites.

A semi-analytical solution for transient confined-unconfined flow toward the partially penetrating well

In this paper, a semi-analytical solution has been proposed for the transient confined-unconfined flow toward a partially penetrating well in a confined aquifer. It can be used to characterize the dynamic development of drawdown and the transient unconfined region during the transient confined-unconfined conversion. The proposed solution takes into account the delayed response recharge from the unsaturated region by the Neuman's upper surface recharge boundary condition, which is derived by the Laplace and Fourier transformations. The reliability of the semi-analytical solution has been proved by comparisons with numerical solutions from Visual MODFLOW Flex. In addition, a new model for the pumping flow in a pure unconfined aquifer is also developed by degradation analysis of the proposed solution, which has been used to fit well with the measured data from the pumping test in Cape Cod aquifer. The results indicate that both the use of partially penetrating pumping well and aquifer anisotropy have negative effects on the drawdown delayed responses and the development of transient unconfined region, which are disappeared at times >105Srb/Kr. The delayed response is positively related to the gravity storage and vertical hydraulic conductivity.

Impacts of Topography‐Driven Water Redistribution on Terrestrial Water Storage Change in California Through Ecosystem Responses

AbstractLateral subsurface flow plays an essential role in sustaining the terrestrial ecosystem, but it is not explicitly represented in most Earth System Models. In this study, we implemented an explicit lateral saturated flow model into the E3SM land model (ELM). The model explicitly describes lateral flow in the saturated zone by representing, for each model grid, an idealized hillslope consisting of five hydrologically connected soil columns. We conducted three model experiments driven by 0.125° atmospheric forcing data during 1980–2015 over California using models of the default ELM, a modified version of ELM to enhance infiltration, and the model with the lateral saturated flow model. The simulated runoff, evapotranspiration, and terrestrial water storage anomaly (TWSA) from the three simulations were evaluated against available observations, and the model explicitly representing lateral flow performs best. The new model produces greater gridcell‐averaged evapotranspiration especially over the mountainous regions with moderate relief and seasonally dry climates. Most importantly, it improves the modeled seasonal variations, interannual variabilities, and the recent decadal decline of TWSA. Many of these improvements can be attributed to the enhanced ecosystem resilience to droughts as demonstrated by transpiration increases caused by lateral flow. Model sensitivity experiments suggest that subsurface runoff is most sensitive to the ratio between horizontal and vertical saturated hydraulic conductivity, followed by hillslope planforms (convergent, divergent, and uniform), number of columns, and lower boundary conditions. Future work should effectively characterize hillslopes in global models and explore the long‐term influences of lateral water movement on modeled biogeochemical cycle.

A Large-Sized Permeameter for Studying Suffusion Characteristics of Anisotropic Soils

Abstract Seepage-induced suffusion involves the migration of fine particles within a soil matrix. Seepage flow is affected by the soil permeability anisotropy of anisotropic soil fabric; however, suffusion anisotropy is unclear because of the limited function of existing permeameters. In recent studies, the effect of seepage direction has been investigated under only low hydraulic gradients because the control of seepage direction relies merely on gravity. In this study, a new, large-sized permeameter is developed with which suffusion tests can be conducted along horizontal or vertical seepage directions under high hydraulic gradients. Correspondingly, the permeameter can accommodate a specimen of 540 × 500 × 470 or 540 × 540 × 440 mm3 (length × width × height). The seepage direction is switched by changing the boundary conditions of the specimen with detachable perforated plates that allow pressurized water originating from different inlets to flow along horizontal or vertical directions. Two repeated pairs of tests were performed on a gap-graded clayey gravel to investigate the suffusion anisotropy of saturated clayey gravel. The results show that the maximum relative deviations of measurements for initial hydraulic conductivity, initiation, and failure hydraulic gradients are less than 3.5 %, demonstrating satisfactory reliability. The ratio of the initial horizontal hydraulic conductivity to vertical hydraulic conductivity for the test soil is 13.87, indicating a significantly anisotropic fabric induced by compaction. The ratios of horizontal initiation and failure hydraulic gradients to vertical initiation and failure hydraulic gradients are 0.52 and 0.59, respectively. This implies that suffusion anisotropy should not be neglected for evaluating the internal instability of anisotropic soils.

Unsteady flow modeling of low-velocity non-Darcian flow to a partially penetrating well in a leaky aquifer system

Previous studies on the flow dynamics of leaky aquifer systems have primarily relied on Darcy's law, assuming fully penetrating wells in confined aquifers. However, when dealing with aquitards dominated by clay, the flow behavior often deviates from Darcy's law. Moreover, in the majority of cases, this entails partially penetrating well pumping. This paper introduces a mathematical model for non-Darcian flow in a confined and partially penetrating well system within a leaky aquifer system. The model is based on the low-velocity non-Darcian flow equation, incorporating the threshold pressure gradient. In the confined aquifer, the flow exhibits two-dimensional Darcian flow behavior, while in the aquitard, the flow is characterized by one-dimensional non-Darcian flow in the vertical direction. In the shallow aquifer, the flow is one-dimensional Darcian flow in the radial direction. The mathematical model is solved using the finite difference method, and the obtained results are compared with calculations based on traditional Darcian flow theory. The findings indicate that the confined groundwater head difference, as predicted by the Darcian and non-Darcian flow theories, diminishes radially as the distance from the pumping well increases and vertically as one moves away from the top of the confined aquifer. As pumping progresses, the confined groundwater head difference initially rises and subsequently stabilizes gradually. Moreover, the magnitude of the confined groundwater head difference is more pronounced when the threshold pressure gradient, vertical hydraulic conductivity of the aquitard, pumping rate, hydraulic conductivity and specific yield of shallow aquifer are larger, or when the hydraulic conductivity and specific storage of the confined aquifer are smaller. The effect of well screen length on the confined groundwater head difference is minimal.

Numerical modeling of vadose zone electrical resistivity to evaluate its hydraulic parameters

Studying and determining the physical properties and hydraulic parameters of vadose zone sediments is an important key to evaluate the infiltration rate into them and assessing the extent to which aquifer sediments benefit from rainwater harvesting in arid and semi-arid areas. Due to the lack of sufficient data on the characteristics of this zone depths, a numerical modeling was used to simulate the electrical resistivity of these sediments by applying the electrical resistivity method, because it is the most affected by the physical properties of dry and wet sediments. This study was applied as a proposal for application in northwestern KSA to calculate the vertical hydraulic conductivity and transmissivity for the vadose zone. This was implemented by assuming a three-layer model using COMSOL Multiphysics model with different electrical resistivity values depending on some in situ electrical resistivity measurements for shallow depths. Hence, the infiltration rate of sediments in this area can be predicted with depth and its effect on aquifer recharge. The focus was on calculating the vertical hydraulic parameters of the most widespread surface sediments with depth and comparing the results of calculating these parameters for some sediments laboratory-wise to ensure their accuracy. Then, their infiltration rate was inferred separately with depth, predicting their ability to aquifer recharge and make the most of rainwater harvesting. Finally, this study can be considered as a preliminary study to determine the expected forward model of electrical resistivity and hydraulic parameters values for the vadose zone sediments with depth along the area and in any other areas, and then apply them accurately in situ to estimate the extent of its usefulness in rainwater harvesting, especially aquifer recharge.

Influence of landscape position and climatic seasonality on soil water and gas conductivity properties in agricultural soils

Agricultural landscape management and climate seasonality can influence soil structure, hydraulic conductivity, and air permeability within the context of soil water and soil gas mobility. To investigate this, in situ and laboratory-based data were collected from three agricultural landscape positions within a watershed in eastern Ontario, Canada during a growing season. Macropore classification, water infiltration tests, and air permeability measurements were conducted in situ and standard soil characterizations were carried out on soil samples. Hydraulic conductivity of the soil matrix, based on grain size data, indicated that the highest values were consistently measured in the B horizon at each landscape setting. Macropores were found to be more abundant within uncultivated drainage ditch bank soils, compared to the adjacent cropped fields. Macropores in the ditch bank soils were exclusively consisted of circular biopores, while both circular and linear macropores were observed in the cultivated field soils. Air permeability, vertical hydraulic conductivity, and horizontal hydraulic conductivity were also greater in the uncultivated soils, relative to the cultivated soils. Field saturated hydraulic conductivity measurements offered evidence of anisotropy, likely due to the vertical nature of the macropore features. Macropore disposition and extent varied over the growing season, especially in the cultivated field soils where tillage and field trafficking are physically disruptive. Seasonality of macropore development will influence temporal changes in advection-based mass exchange of gas and water in the vadose zone. Modeling of mass exchange in agricultural soils should consider time variability in macroporosity to more realistically characterize infiltration and soil gas emissions.

Kaolinite Deposition Dynamics and Streambed Clogging During Bedform Migration Under Losing and Gaining Flow Conditions

AbstractClogging of streambeds due to clay deposition influences the stream‐subsurface exchange flux and thus directly modulates hyporheic ecological and biogeochemical processes. Clogging of sandy streambeds has previously been studied under losing and gaining flows and during streambed movement, but not when these two flow conditions coincided. We conducted flume experiments to quantify the combined effect of moving bedforms and losing or gaining flows on kaolinite deposition and streambed clogging. The experiments were conducted by adding pulses of kaolinite in a flume packed with sand under a stream water velocity of 25 cm/s. We measured the deposition rates, dynamics of hyporheic exchange flux (HEF) and vertical hydraulic conductivity (Kv), and the vertical distribution of kaolinite at the end of the experiments under two losing and two gaining flows (Darcy velocity of 10 and 20 cm/day). Kaolinite deposition led to clogging and reduction in Kv and HEF under all flow conditions. Deposition occurred faster under losing flow conditions than under gaining flow conditions. However, the changes in Kv and HEF were similar under losing and gaining flow conditions for similar kaolinite concentrations in the bed. Our results indicate that the deposition patterns of kaolinite were more influenced by bedform movement than by losing or gaining flow conditions, which is markedly different from the behavior observed under losing and gaining conditions for stationary bedforms. This implies that bedform morphodynamics control local‐scale clogging of sandy streambeds and should be accounted for when studying the hydrology of catchments at larger scales.

An Application of Inverse Problem and Universal Solutions for Pumping Wells in Unconfined Aquifers

As far as we know, universal solutions (or type-curves) for scenarios of flow through anisotropic unconfined aquifers due to pumping wells cannot be found in the literature. On the contrary, those theoretical solutions in hydrogeological manuals are commonly based on Dupuit solutions for isotropic soils or simplifying other characteristics of the chosen medium. In this study, the application of the discriminated nondimensionalization technique allowed for the inclusion of vertical and radial hydraulic conductivities in the data set, with which the monomials ruling unknown variables of the problem, pumping flow and seepage surface in their dimensionless form are obtained. One of the main findings of this research is depicting these relationships as type-curves from a large number of precise numerical simulations based on the Network Simulation Method. The other main finding is an easy-to-apply methodology to estimate vertical and radial hydraulic conductivities employing these type-curves. This methodology can be considered as an inverse problem. In addition, an example of the problem is presented, in which the influence that measure deviations may have on the estimated values of the hydraulic conductivities in anisotropic soils is also studied and discussed.

Numerical investigation of coupled density-driven flow and hydrochemical processes in coastal aquifers influenced by storm surges

Storm surges can result in significant damage to coastal aquifers. Studies have investigated groundwater salinization caused by storm surge inundation. However, the phenomenon of evaporation-driven mineral precipitation in saltwater lakes has not received much attention in the literature. To address this gap, this study simulated the impact of saltwater lakes formed after a storm surge on coastal aquifers by coupling the PHREEQC and SEAWAT models. Six scenarios were considered, with varying lake depth, area, evaporation rate and vertical hydraulic conductivity of lakebed. The results indicate that the total dissolved solids (TDS) and water level of saltwater lake are subject to constant changes due to evaporation. Scenario 2, with the smallest lake area exhibited the least susceptibility to evaporation, with a maximum TDS concentration in the lake of ∼86 g/L, and only dolomite and calcite reached saturation. However, infiltration of saline water into the aquifer was higher than for the other scenarios. A comparing of scenarios with different vertical hydraulic conductivities of lakebed (scenarios 5 and 6 have conductivities that are 0.1 × and 0.01 × that of scenario 1, respectively) shows that a smaller vertical hydraulic conductivity leads to less saline infiltration into the aquifer, but a greater amount of salt precipitates (precipitation ratios of 1.03%, 1.92%, and 5.73% for scenario 1, 5 and 6, respectively). The results of scenario 4, which has double the evaporation rate of the other scenarios, indicate that evaporation leads to significantly greater salt precipitation and a corresponding decrease in the amount of salt that enters the aquifer. The results of secondary salinization indicate that salt precipitated on the surface may infiltrate the aquifer through rainfall dissolution, causing groundwater to become saline again. These findings emphasize the importance of accounting for the impact of evaporation on saltwater lake dynamics and coastal groundwater salinization in future studies.