Lateral Flows Research Articles

Hyper‐Resolution Continental‐Scale 3‐D Aquifer Parameterization for Groundwater Modeling

AbstractGroundwater is the world's most important freshwater resource. Despite this importance, groundwater flow and interactions between groundwater and other parts of the hydrological cycle are often neglected or simplified in large‐scale hydrological models. One of the challenges in simulating groundwater flow and continental to global scales is the lack of consistent globally available hydrogeological data. These input data are needed for a more realistic physical representation of the groundwater system, enabling the simulation of groundwater head dynamics and lateral flows. A realistic representation of the subsurface is especially important as large‐scale hydrological models move to finer resolutions and aim to provide accurate and locally relevant hydrologic information everywhere. In this study, we aim at improving and extending on current available large‐scale data sets providing information of the subsurface. We present a detailed aquifer representation for the continental United States and Canada at hyper resolution (250 × 250 m). We integrate local hydrogeological information, including observations of aquifer layer thickness, conductivity, and vertical structure, to obtain representative aquifer parameter values applicable to the continental scale. The methods used are simple and can be expanded to other parts of the world. Hydrological simulations were performed using the integrated hydrological model ParFlow and demonstrated improved model performance when using the new aquifer parameterization. Our results support that more detailed and accurate aquifer parameterization will advance our understanding of the groundwater system at larger scales.

Frequency Shift of Near-Inertial Waves in the South China Sea

AbstractDespite sufficient wind forcing, internal waves in the South China Sea do not exhibit the strong near-inertial wave (NIW) peak that is typical in most of the world oceans. Using data from 10 contemporaneous moorings deployed in summer 2011, we show that strong isopycnal vertical tidal displacements transfer most of the near-inertial (NI) kinetic energy (KE) to frequencies higher than the inertial frequency in an Eulerian reference frame. Transforming to an isopycnal-following reference frame increases the KE at NI frequencies, suggesting the presence of NIWs. However, the projection onto a semi-Lagrangian coordinate system still underestimates the expected NI peak. To fully resolve NIWs requires the use of time-dependent vertical wavenumber–frequency spectra because the intrinsic frequency of the NIWs varies substantially, owing to Doppler shifting by lateral mesoscale flows. Here, we show NIW intrinsic frequency variations of ±0.2 cpd within few days, of similar magnitude as the observed variations of relative vorticity associated with the meandering Kuroshio.

The influence of lateral flows in an aquifer on the agricultural value of groundwater

AbstractValuation of water in an aquifer depends on reliable information about the hydrologic conditions of an aquifer. Regions of depression emerge in an aquifer because groundwater cannot seamlessly flow between shallow and deep aquifer locations, and our analysis shows that the degree of lateral flow influences the value of the water in the aquifer. The assumption that groundwater declines uniformly over a landscape, a bathtub aquifer, leads to an underestimate of the value of a unit of water in an aquifer but an overestimate of the wealth that the aquifer represents. For the alluvial aquifer in Arkansas, USA, the average accounting price of water in an aquifer is almost 40% higher if there is no lateral flow, but the groundwater wealth is 10% lower. The value of an aquifer with the limited lateral flow is less sensitive to changes in agricultural markets, the discount rate, or the natural recharge of the aquifer.Recommendations for Resource Managers Average value of water in an aquifer with limited lateral flows is nearly 40% higher than the value of an aquifer with high lateral flows. Groundwater wealth weights the accounting prices of water in the aquifer by the amount water underneath each site. As lateral flows decline, the wealth of the aquifer rises and then falls because the distribution of accounting prices change so most water is beneath sites with lower accounting prices. The average value of water in an aquifer is less sensitive to changes in hydro‐economic model parameters such as the natural recharge or discount rate when the lateral flows are less.

Mean transit time and subsurface flow paths in a humid temperate headwater catchment with granitic bedrock

Headwater catchments make a considerable contribution to the discharge of whole stream networks and mean transit time (MTT) is a fundamental factor affecting flow and storage in the hydrologic system. We estimated the MTT along with the identification of subsurface water flow processes using time series measurements of stable isotopes and major solutes in the water of a small mountainous catchment with granitic bedrock under a humid temperate climate. The MTT was estimated to be 1.1–1.7 years, 0.5–0.8 years, and 1.5 years for stream water at the catchment outlet and first-order tributaries, soil water, and shallow groundwater, respectively, based on sinusoidal variation in deuterium excess in the hydrologic components and precipitation. The MTT of first-order streams was negatively correlated with the topographic gradient of the sub-catchments. The SiO2(aq) and Cl− concentrations in first-order streams were used to discriminate dominant subsurface flow contributing to the streams, depending on the topographic gradient. Soil water had a higher seasonal variability in SiO2(aq) and Cl− concentrations, which were controlled by rainfall infiltration, whereas shallow groundwater had significantly lower seasonal variability, with a depleted isotopic signature, suggesting the contribution of lateral water flows from the upgradient area. The increased seasonal variation in SiO2(aq) and Cl− concentrations with increasing MTT in first-order streams indicated that the storage capacity and flow paths in the soil layer were determining factors for subsurface water flow in hillslope areas. Seasonal variation in the SiO2(aq) concentration at the catchment outlet revealed a major contribution of subsurface flow to stream discharge as lateral flow through the soil–bedrock interface and an interflow through the soil layer in the dry and rainy seasons, respectively. Through the integration of the MTT and seasonal variation in hydrogeochemical parameters in soil water, stream water, and groundwater, this study demonstrates that soil depth and the soil–bedrock interface were the main controls on streamflow generation in a headwater catchment with a crystalline bedrock.

Managed Aquifer Recharge of Monsoon Runoff Using Village Ponds: Performance Assessment of a Pilot Trial in the Ramganga Basin, India

The managed aquifer recharge (MAR) of excess monsoonal runoff to mitigate downstream flooding and enhance groundwater storage has received limited attention across the Indo-Gangetic Plain of the Indian subcontinent. Here, we assess the performance of a pilot MAR trial carried out in the Ramganga basin in India. The pilot consisted of a battery of 10 recharge wells, each 24 to 30 m deep, installed in a formerly unused village pond situated adjacent to an irrigation canal that provided river water during the monsoon season. Over three years of pilot testing, volumes ranging from 26,000 to 62,000 m3 were recharged each year over durations ranging from 62 to 85 days. These volumes are equivalent to 1.3–3.6% of the total recharge in the village, and would be sufficient to irrigate 8 to 18 hectares of rabi season crop. High inter-year variation in performance was observed, with yearly average recharge rates ranging from 430 to 775 m3 day−1 (164–295 mm day−1) and overall average recharge rates of 580 m3 day−1 (221 mm day−1). High intra-year variation was also observed, with recharge rates at the end of recharge period reducing by 72%, 88% and 96% in 2016, 2017 and 2018 respectively, relative to the initial recharge rates. The observed inter- and intra-year variability is due to the groundwater levels that strongly influence gravity recharge heads and lateral groundwater flows, as well as the source water quality, which leads to clogging. The increase in groundwater levels in response to MAR was found to be limited due to the high specific yield and transmissivity of the alluvial aquifer, and, in all but one year, was difficult to distinguish from the overall groundwater level rise due to a range of confounding factors. The results from this study provide the first systematic, multi-year assessment of the performance of pilot-scale MAR harnessing village ponds in the intensively groundwater irrigated, flood prone, alluvial aquifers of the Indo-Gangetic Plain.

Initiation of dilute and concentrated pyroclastic currents from collapsing mixtures and origin of their proximal deposits

Numerical solution of the time-dependent conservation equations for mass, momentum, specific internal energy, and granular temperature in flows involving gas-particle mixtures is used to explore the initiation of pyroclastic currents from collapsing mixtures such as during fountaining eruptions. One objective is to determine when a depth-averaged granular flow model or a box model for dilute currents is most applicable for hazards modeling of pyroclastic currents produced by column collapse; a second objective is to gain insight into the formation of proximal breccia facies of ignimbrites. Collapsing gas-particle mixtures impacting a flat surface are modeled with mixtures of coarse particles that are poorly coupled with the gas phase and well-coupled fine particles. Resulting lateral flows are sensitive to the impact speed, overall particle concentration, and proportions of fine and coarse particles. For total particle concentrations of around 1 vol.%, an impacting mixture consisting of at least ~ 50% coarse particles, relative to fines, will tend to form a concentrated lateral underflow, which can be approximated by a depth-averaged granular flow model for hazard assessment purposes starting from the impact zone. Low total particle concentrations (e.g., total concentrations of ~ 0.1 vol.%) tend to produce dilute lateral flows that could be simplified to box model approaches for dilute pyroclastic currents. Larger total particle concentrations in impacting mixtures (~ 10 vol.%) produce granular underflows if they have any coarse particles, but these can be complicated by Mach number effects. For intermediate concentrations of the impacting mixture, a rough threshold for development of a concentrated underflow versus a dilute-only current is based upon the flux per unit area of coarse particles to the impact and their Stokes numbers. In general, some knowledge of the eruption column (fountain) conditions is required in order to make an informed decision as to which hazards modeling approach is most applicable for a given scenario. Modeling indicates that proximal breccias are related to influxes of coarse wall-rock material into an eruptive mixture, which increase both the total particle concentration and the proportion of coarse, dense clasts in the mixture that subsequently collapses and impacts the ground. The breccias record concentration of dominantly coarse clasts immediately upon impact and formation of concentrated flows that propagate laterally while expelled fines and gas flow rapidly overhead as dilute currents. Lateral and vertical heterogeneity in proximal deposits likely record rapid time and space variations in avalanches of material into eruptive vents, and the occurrence of breccia hummocks might record the temporary positions of impact zones.

Transgressive Sills and Lateral Lava Flows: On the Visual Observation of Igneous Sheets in Rugged Mountainous Terrains and the Optical Illusion Factor

Transgressive sills are of common occurrences in rift-related offshore and onshore sedimentary settings worldwide and have been reported in onshore volcanic settings in e.g. flood basalt provinces as well. General geometries of individual sills and of entire sill complexes too are well documented from seismic images in many offshore sedimentary settings of exploration interest, but limitations in seismic resolution may inhibit correct interpretations when it comes to small-scale structures and evidences on sill intrusion modes. Hence, relevant and important details and clues on intrusion mechanisms during emplacement of sheet intrusions, which may be unclear or missing in seismic images from offshore sedimentary basins, can to some degree be clarified by means of thorough visual examination and measurements on exposed onshore sills and sill complexes. In the actual study, relevant visual observations and measurements of the Streymoy Sill and its feeders in particular and to a lesser degree the Eysturoy Sill of the Faroe Islands, as well as some local lava flows, are scrutinised in order to demonstrate the importance of correct and detailed mapping, associated measurements and interpretations at exposed sill margins. The actual study chiefly focuses on potential optical illusion factors, not uncommon for sheet intrusions in rugged mountainous terrain, and potential associated misinterpretations. It is shown that unless due care is taken in assuring that sub-horizontal visual observations from some distance in such terrains are duly accompanied by other observations in the sub-vertical and/or sub-lateral plane at other angles as well, i.e. proper 3-D considerations, noticeable errors could result, when it comes to interpretations on intrusion mechanisms and possible regional stresses that prevailed during emplacement of such sheet-like igneous bodies.

Correlation-based Doppler-angle estimation with plane-wave excitation

Abstract Conventional Doppler imaging does not provide angle information, which makes it difficult to obtain flow information, especially for lateral flows. A correlation-based transit-time approach has been developed for estimating the Doppler angle under the framework of a focused-beam architecture, which has a fast computation capability. However, there is still a trade-off between the estimation accuracy and data acquisition time, and so this study applied plane-wave excitation with the aim of mitigating this limitation. In addition, three Doppler-angle estimation methods based on (1) the fast Fourier transform, (2) correlation, and (3) an autoregressive model were used to estimate Doppler angles. The estimation performances and computation loads of the three approaches were compared using simulations and a flow phantom. The simulation results showed that the Doppler angle can be correctly estimated with a sufficient aspect ratio, and Doppler-angle estimation using plane-wave excitation outperformed the focused-beam method. The flow-phantom experiments revealed the minimum number of ensembles required for the different approaches. The velocity-vector profiles were also demonstrated using the correlation and autoregressive methods, to show the feasibility of both lateral and axial velocity estimation using the proposed methods.

First order multi-lane traffic flow model – an incentive based macroscopic model to represent lane change dynamics

ABSTRACTUnbalanced lane usage on motorways might lead to the reduction in capacity of the motorway. Lane-level traffic management present new opportunities to balance the lane-flow distribution and help reduce congestion. In order to come up with efficient traffic management strategies on a lane-level, there is a need for accurate lane-specific traffic state estimation models. This paper presents a first-order lane-level traffic flow model. The proposed model differs from the existing models in the following areas: (i) incentive-based motivation for lane changes and consideration of downstream conditions (ii) transfer of lateral flows among cells. The model is tested against real-world data. It is observed that the model is able to capture the lane-level dynamics in terms of the lane flow distribution. The model results are compared to a linear regression model and results show that the developed model performs better than the regression model on the test sections.

Suppression of Capillary Flow in Slot-Die Coating for the Fabrication of Fine OLED Stripe

Due to lateral and vertical capillary flows appearing in a slot-die head with $\mu $ -tip for fine line coating, line breakup occurs at a relatively low coating speed, making it difficult to narrow the stripe. Through computational fluid dynamics (CFD) simulations, we demonstrate that capillary flow can be substantially suppressed by increasing the contact angle of the head lip and forming the microscale groove patterns in the dual plate (shim and meniscus guide). It is shown that the corresponding contact angle of the groove patterns increases up to 120°. Based on the simulation results, we have coated the head lip with a hydrophobic material and embedded the dual plate with micropatterns fabricated by a laser cutter into the slot-die head. Using such a hydrophobic slot-die head, we can suppress the lateral capillary flow of an aqueous poly(3,4-ethylenedioxythiophene):poly (4-styrenesulfonate) (PEDOT:PSS) to a great extent and, hence, increase the coating speed, rendering the stripe narrow ( $\approx 76~\mu \text{m}$ ). To demonstrate its applicability to organic light-emitting diodes (OLEDs), we have also fabricated fine red, green, and blue OLED stripes and successfully achieved light emission from them with the emission area of $80\,\,\mu \text{m}\,\,\times {5}$ cm.

Nondestructive three-dimensional observations of flow finger and lateral flow development in dry snow using magnetic resonance imaging

Flow fingers develop due to the infiltration of snow meltwater or rain water into a dry snowpack. The width, spacing, and areal coverage of the flow finger path and occurrence of capillary barriers have been demonstrated using dye tracer experiments that were conducted in the field and in cold laboratories. Because dye tracer experiments require the destructive analysis of the snow, the initial shape, and the temporal development of fingering and lateral flows are unclear. To examine this, we carried out nondestructive observations of flow finger development, and the formation of capillary barriers using two different dry snow samples in a cold laboratory using magnetic resonance imaging (MRI) with a three-dimensional rapid imaging method. X-ray micro-computed tomography (μCT) was also used to determine the relationship between the water flow phenomena and the snow microstructure. The experimental results showed that flow fingers developed in dry snow samples. The number of flow finger paths increased, and a lateral flow developed through the continuing water supply. The small discontinuity of the pore size and snow density in the vertical direction acted as a capillary barrier and induced lateral flow. These results showed that both the persistence of the flow finger path and the increase in the number of flow paths are important for understanding the infiltration of water into dry snow and for developing a snowpack model that includes water-moving processes. Nondestructive observation using MRI is a promising technique to follow the development of preferential flow path and lateral flow. Detailed information regarding the heterogeneity of the pore distribution and snow microstructures in a layered snowpack is required to understand the water flow phenomena in a natural snowpack.

Spatially distributed sensitivity of simulated global groundwater heads and flows to hydraulic conductivity, groundwater recharge, and surface water body parameterization

Abstract. In global hydrological models, groundwater storages and flows are generally simulated by linear reservoir models. Recently, the first global gradient-based groundwater models were developed in order to improve the representation of groundwater–surface-water interactions, capillary rise, lateral flows, and human water use impacts. However, the reliability of model outputs is limited by a lack of data and by uncertain model assumptions that are necessary due to the coarse spatial resolution. The impact of data quality is presented in this study by showing the sensitivity of a groundwater model to changes in the only available global hydraulic conductivity dataset. To better understand the sensitivity of model output to uncertain spatially distributed parameters, we present the first application of a global sensitivity method for a global-scale groundwater model using nearly 2000 steady-state model runs of the global gradient-based groundwater model G3M. By applying the Morris method in a novel domain decomposition approach that identifies global hydrological response units, spatially distributed parameter sensitivities are determined for a computationally expensive model. Results indicate that globally simulated hydraulic heads are equally sensitive to hydraulic conductivity, groundwater recharge, and surface water body elevation, though parameter sensitivities vary regionally. For large areas of the globe, rivers are simulated to be either losing or gaining, depending on the parameter combination, indicating a high uncertainty in simulating the direction of flow between the two compartments. Mountainous and dry regions show a high variance in simulated head due to numerical instabilities of the model, limiting the reliability of computed sensitivities in these regions. This is likely caused by the uncertainty in surface water body elevation. We conclude that maps of spatially distributed sensitivities can help to understand the complex behavior of models that incorporate data with varying spatial uncertainties. The findings support the selection of possible calibration parameters and help to anticipate challenges for a transient coupling of the model.

Effect of Broiler Litter Application Method on Metal Runoff from Pastures

Loss of metals from agricultural fields to surface water bodies causes deterioration of surface water quality. Method of application of broiler litter can affect loss of metals in surface runoff. Subsurface banding of broiler litter can decrease loss of P and N in surface runoff relative to surface application of broiler litter. However, limited research has been done to evaluate the impact of litter application method on loss of metals in surface runoff. Therefore, the objective of this research was to quantify differences in loss of metals in surface runoff from a tall fescue pasture as a function of method of application of broiler litter (i.e., surface vs. subsurface application). A rainfall simulation study was conducted in the Sand Mountain region of north Alabama. Results indicate that concentration and loadings of Cu, K, Mg, and Zn decreased in surface runoff as a result of application of broiler litter in subsurface bands and were similar between the subsurface‐banded broiler litter and control (no litter applied) treatments. Greater than 90% of the applied rainfall infiltrated, indicating that losses of metals via lateral and subsurface flows can be substantial. Overall, results of this study show that application of broiler litter in subsurface bands can reduce loss of metals in surface runoff. Future research studies should investigate the impact of method of application of broiler litter on the metal losses in leachate and subsurface flows.Core Ideas Broiler litter application method affects loss of metals in runoff. Subsurface banding of broiler litter reduced concentrations of metals in runoff. Loss of metals via lateral flow pathways could be significant in this region.

Porosity gradients as a means of driving lateral flows at cometary surfaces

The Rosetta spacecraft has provided invaluable and unexpected information about cometary outgassing. The on-board instruments ROSINA, MIRO, and VIRTIS showed non-uniform outgassing of H2O over the surface of the nucleus. Rarefied gas flows display remarkable flow phenomena that may help explain diverse physical observations and models have been used in various engineering applications. Typical examples are flows generated by temperature variations such as thermal creeping flows that may have applications in cometary research. In this paper, we demonstrate how porosity variations in a porous medium combined with rarefaction can also lead to high tangential speed flow at a surface. Outgassing through a porous surface layer has been postulated as one possible mechanism at the cometary surfaces. We use the Direct Simulation Monte Carlo (DSMC) method to investigate such flows. The porous media structure consists of micro computed tomography (micro-CT) image of real Earth rock samples with high resolution. We show that lateral gas density gradients can be produced in a straightforward manner leading to substantial non-radial flow.

Development of water and energy Budget-based Rainfall-Runoff-Inundation model (WEB-RRI) and its verification in the Kalu and Mundeni River Basins, Sri Lanka

Distributed Hydrological Models (DHMs) with the capability of simulating catchment-scale water and energy budgets as well as rainfall-runoff-inundation processes are essential tools for Integrated Water Resource Management (IWRM) as well as Water-related Disaster Risk Reduction (WDRR) under changing climate. This research developed a new DHM, the Water and Energy Budget-based Rainfall-Runoff-Inundation (WEB-RRI) model, by integrating the RRI model’s diffusive wave flow equations into a land surface model (hydro-SiB2) to incorporate water and energy budget processes, land-vegetation-atmosphere interactions, soil moisture dynamics, and 2-D lateral water flows to improve interception, evapotranspiration (ET), soil moisture, runoff, and inundation processes. The performance of the new model was assessed using river discharge data, MODIS and GLEAM ET data, and ground as well as satellite inundation extents in the Kalu (wet) and Mundeni (dry) River basins in Sri Lanka. The model was well calibrated and validated (Nash > 0.9) and confirmed to be highly capable of reproducing the long-term (~20 years) observed river discharges (Nash > 0.89) and hydrological flow regime properties for both basins. Particularly, the simulated low flow just before the flood and the peak discharges during the flood, as well as their timings, coincided well with the observed discharges in both basins, which indicates that the model is capable of reproducing soil and vegetation water storages reasonably well, and therefore it can be used for real-time and forecasting applications with the re-starting capability. The model-simulated basin averaged ET fluxes and their trends agreed better with GLEAM (RMSE: ~0.7–0.95 mm/day, correlation: ~0.35–0.39) than with MODIS (RMSE: ~0.96–1.04 mm/day, correlation: ~0.14–0.25). The simulated inundation extents were also consistent with the ground- and MODIS-driven inundation extents. The future focus of this research will be on expanding the model applicability for basin-wide IWRM and WDRR, including flood- and drought-related risk assessments, by employing the model to operational applications (e.g., flood forecasting and seasonal flow prediction) and long-term applications (e.g., catchment responses to past and future climatology, water cycle variability, hydrological extremes, and land-use changes).

Uncertainty comparison of velocity estimators for ultrasound flow imaging in narrow channels / Messunsicherheitsvergleich von Geschwindigkeitsschätzern der Ultraschallströmungsbildgebung in schmalen Kanälen

Abstract Ultrasound Imaging with a linear phased array allows measuring turbulent vector profiles in two dimension with two components (2D2C). This is interesting in narrow channels for the application in battery cells or research in magnetohydrodynamics (MHD), where the access to the opaque fluid is often restricted. There are two main velocity estimation methods applicable: the Ultrasound Doppler Velocimetry (UDV) or the Ultrasound Image Velocimetry (UIV). In this work, these methods were evaluated by their attainable measurement uncertainty for the application in narrow channels, where the acquisition of the lateral velocity component is crucial. With a calibration rig, UIV could achieve a total measurement uncertainty of 9.9% and UDV 17.6%. As UIV reaches a 44% lower measurement uncertainty, it is the preferential method to measure lateral flows in narrow channels. In future work, the calibration rig will be adapted to optimize and characterize the flow instrumentation in opaque liquid metals.

Long-length YBCO coated conductors for ultra-high field applications: gaining engineering current density via pulsed laser deposition/alternating beam-assisted deposition route

Gaining engineering critical current density (Je) in high-temperature superconducting (HTS) coated conductors based on double-disordered YBCO for operation at high fields is one of the key requirements in upcoming magnet/accelerator projects. Currently, the development of a tape with advanced Je-s is performed based on an alternating beam-assisted deposition–pulsed laser deposition (ABAD–PLD) manufacturing route. An obvious way to improve Je-s is to reduce substrate thickness. A 40% Je increase is expected owing to the thickness reduction from 100 to 50 μm. Nevertheless, the reduction of substrate thickness in case of the applied processing technology that employs relatively thick (2–3 μm) yttria-stabilized zirconia buffer layers leads to the manifestation of considerable strain in the tape resulting in strong tape bowing. Advanced processing routes have been developed to suppress this effect. The highest engineering current density was recorded at well above 1000 A mm−2 under an ultra-high field of 18 T at 4.2 K, B//c. Influence of tape bowing and the impact of longitudinal defects are studied via V–I measurements at 77 K and a moderate magnetic field with intrinsic edge gradients. Potential for further gaining of Je was found employing mechanisms of (i) film nucleation from lateral flows that provide material transfer during the PLD process. Further steps include suppressing the instability of instantaneous temperature via quasi-adiabatic pulsed heating of the growing HTS film via (ii) control of laser plume energy, and (iii) energy release during film condensation (condensation enthalpy). These effects disturb the instantaneous temperature of the growing HTS layer, which exhibits very limited capability of heat transfer. Temperature pulses reaching 30–40 K were evaluated via heat transfer modeling. Stabilization of the level of pulsed temperature during layer growth is anticipated to result in a further increase in Je.

Challenges in developing a global gradient-based groundwater model (G<sup>3</sup>M v1.0) for the integration into a global hydrological model

Abstract. In global hydrological models, groundwater (GW) is typically represented by a bucket-like linear groundwater reservoir. Reservoir models, however, (1) can only simulate GW discharge to surface water (SW) bodies but not recharge from SW to GW, (2) provide no information on the location of the GW table, and (3) assume that there is no GW flow among grid cells. This may lead, for example, to an underestimation of groundwater resources in semiarid areas where GW is often replenished by SW or to an underestimation of evapotranspiration where the GW table is close to the land surface. To overcome these limitations, it is necessary to replace the reservoir model in global hydrological models with a hydraulic head gradient-based GW flow model. We present G3M, a new global gradient-based GW model with a spatial resolution of 5′ (arcminutes), which is to be integrated into the 0.5∘ WaterGAP Global Hydrology Model (WGHM). The newly developed model framework enables in-memory coupling to WGHM while keeping overall runtime relatively low, which allows sensitivity analyses, calibration, and data assimilation. This paper presents the G3M concept and model design decisions that are specific to the large grid size required for a global-scale model. Model results under steady-state naturalized conditions, i.e., neglecting GW abstractions, are shown. Simulated hydraulic heads show better agreement to observations around the world compared to the model output of de Graaf et al. (2015). Locations of simulated SW recharge to GW are found, as is expected, in dry and mountainous regions but areal extent of SW recharge may be underestimated. Globally, GW discharge to rivers is by far the dominant flow component such that lateral GW flows only become a large fraction of total diffuse and focused recharge in the case of losing rivers, some mountainous areas, and some areas with very low GW recharge. A strong sensitivity of simulated hydraulic heads to the spatial resolution of the model and the related choice of the water table elevation of surface water bodies was found. We suggest to investigate how global-scale groundwater modeling at 5′ spatial resolution can benefit from more highly resolved land surface elevation data.

Uniform and lateral preferential flows under flood irrigation at field scale

AbstractFlood irrigation is globally one of the most used irrigation methods. Typically, not all water that is applied during flood irrigation is consumed by plants or lost to evaporation. Return flow, the portion of applied water from flood irrigation that returns back to streams either via surface or subsurface flow, can constitute a large part of the water balance. Few studies have addressed the connection between vertical and lateral subsurface flows and its potential role in determining return flow pathways due to the difficulty in observing and quantifying these processes at plot or field scale. We employed a novel approach, combining induced polarization, time‐lapse electrical resistivity tomography, and time‐lapse borehole nuclear magnetic resonance, to identify flow paths and quantify changes in soil hydrological conditions under nonuniform application of flood irrigation water. We developed and tested a new method to track the wetting front in the subsurface using the full range of inverted resistivity values. Antecedent soil moisture conditions did not play an important role in preferential flow path activation. More importantly, boundaries between lithological zones in the soil profile were observed to control preferential flow pathways with subsurface run‐off occurring at these boundaries when saturation occurred. Using the new method to analyse time‐lapse resistivity measurements, we were able to track the wetting front and identify subsurface flow paths. Both uniform infiltration and preferential lateral flows were observed. Combining three geophysical methods, we documented the influence of lithology on subsurface flow processes. This study highlights the importance of characterizing the subsurface when the objective is to identify and quantify subsurface return flow pathways under flood irrigation.

Investigation of humping defect formation in a lap joint at a high-speed hybrid laser-GMA welding

Abstract Productivity rise can be realized at high-speed welding, but in a practice, the constraints emanate from the tolerance welding speed limit beyond which generate humping defects and the likes. These defects are undesirable in welding as they undermined the weld bead integrity and decrease productivity. In this study, an investigation on a lap joint welding using a hybrid Laser-GMAW (L-GMAW) welding process on a carbon steel sheet was undertaken to examine the mechanisms involved in the arc behavior, the droplet transfer, and the weld pool flow dynamics in a hump defect formation at high-speed welding. A variation of the process parameters in the hybrid welding system such as the wire feed speed (WFS), the traveling speed (TS) and the oscillation of the laser beam were used as input signals. A high-speed video camera was used with different viewing positions to capture the sequence of events during the hybrid welding process. The high-speed images of the arc behavior, the weld pool flow pattern with the use of tracer particles in arriving at the root mechanisms were acquired. Based on the experimental resultant, the occurrence mechanisms of the weld defects were proposed. In this study, the key factors in the humping defect formation are the two dominant lateral flows toward the top and bottom sheets, the collision between the weld pool back- and rear-flow and the interruption of the weld pool flow channel. Also, the generation of copious spatter due to the two lateral flows and the swollen buildup towards the hump closure were responsible for the next hump initiation formation. The beam oscillation applied to wet the weld toe angle to delay the outset of the humping defect occurrence was insignificant at higher travel speed. Furthermore, the force of gravity and surface tension were the key forces in this study.